30 May 2013

Amps: Koch Studiotone combo revalved, finally!


Note: this entry was already published in my old Spanish version of this blog, around Juny 2011. I am just revisiting it here.

Of all the amps I've retubed this, without any doubt, is the one that more headaches gave me. Around 60 tube swap testings, throwing there anything I had in stock and even, purchasing new tube types to check any possible combination and, I was stuck for around 3 weeks.
After trying everything, some light shone in my head: am I doing it well?.
I went to user's manual and, I thought it would be a good idea to get a couple of the setting samples in that manual and test the tubes with those amp settings that I would probably use the most: Blues (Hard Rock) and Metal.

So, while reviewing the settings, I've realized that the Mids Shift switch worked in inverse mode as I thought. Position (+) is where we have natural mids, while in position (.) we have recessed mids.
Oh my God!, I was trying to get a decent Hard Rock sound with recessed mids!.
Well, after fighting with tubes and, after a bunch of tube swapping I've learnt some lessons that I would like to record in this entry (for my own use, mainly).

Lesson 1: carefully read the User's Manual before starting.

If you have a hi gain amp or any other kind of amp with a complex front end, search the settings that better suit your habitual style. Theoretically, you should be able to select the right tubes with those setting suggested by the maker.
One more thing that took my attention is that no sample setting in the manual had a Volume greater than position at 10:00h, while I was trying with volumes far away the 2:00h.
(see lesson 1)
It seems that, until 9h, the power section remains clean, without distortion but, beginning in 10h, the power section starts to break up and, every little touch in Volume overloads the PI tube and, power tubes exponentially so, in fact, only with very low gain settings you can roll on high volumes.

Alright!. After discovering that I was wasting my time, due to the fucking Mid Shift switch, I've decided to start from scratch, with following criteria:

  • To leave a Sovtek 12AX7-LPS in the PI position (V3, PI or Diver)
  • To leave a matched pair of JJ EL84 in the power tubes, since they are very standard.
  • To use a pair of the maker' suggested settings as a comparison starting point: Blues and Metal settings.
Since the amp is very versatile and ambitious respect to available voices, I tried to center myself in the two closer styles to my taste but, in case of doubt, I will choose the tubes that better work for Blues/Hard Rock, what I like it more.

Lesson2: In amps with simple design, changes in pre-amp are way drastic than in complex front-end amps.

In simple-design amps, it's very difficult to get a wrong sound when working with the EQ but, in complex front-end amps, it's way easier to get wrong sounds if you don't carefully tweak ALL controls at same time.
In simple amps, it's very easy to identify a tube that will bring you exactly the character you wanted for that amp but, complex amps seem to like better neutral and even tubes, so they can cover any of the possible voices. The amp will not shine in any particular mode in that way but, it could cover any ground with an usable voice, instead.

After trying it with the suggested settings, it was clear to me that my issues with excessive feedback and squealing where directly related to power stage, not with pre-amp stage.
Looking to the blocks schema of this amp, the Volume control was placed after the two pre-amp tubes (V1, V2) and, before the Phase Inverter (V3).
So, the Gain control is regulating the saturation control of EVERY pre-amp tube, while the Volume control regulates the saturation level of the PI and, consequently of the power tubes.
That means that, if we already have the pre-amp with a high gain level, the original signal was highly amplified and distorted so, we would need to deliver smaller levels to the power tubes, where it will be exponentially amplified.

Every time that the Volume knob is below 10:00h, all squealing and excessive feedback issues go away.
Once we reached some Gain level, any increase of the Volume knob doesn't give us a great difference in loudness level but, maybe a higher degree of distortion of the PI and power tubes, increasing the feedback and squealing.

Lesson 3: draw a scheme with the gain cascade of your amp and, understand how pre-amp and power stages interactue between themselves.

Pre-amp tubes


On amp's schema, first tube was labeled as 12AX7LM.
According to Koch Techs, they are currently mounting a JJ ECC83S in factory, not because of its sounding quality but, more because it can get rid of most of microphonics issues (and, I bet that it's also because it's cheap). Additionally to this, it's high output ratio helps to feed the rest of this complex front end.
It's gain level isn't so high as in other tubes and, therefore it can help to lower a bit the overall loudness of this amp.
There are some other alternative tubes that are specially good to solve microphonics issues in V1.
By definition, any 7025 is specially good for microphonics issues (even that sonically cannot be the best option).
A NOS 5751 can work also there but, it has a gain factor of 70 (instead of the nominal 100 of 12AX7 specification), that gives some headroom for cleans.
But, also in current production 12AX7 tubes, there are a few that work very well related to microphonics:

  • Mullard 12AX7 re-issue, this one has an excellent harmonic content and note-to-note definition (but works better when pushed hard). Not a great output level, instead so, it cannot work for complex front-ends.
  • Tung Sol 12AX7 re-issue, this one has big bottom end and cutting high end, good gain and output levels but, not so defined as the Mullard..
  • Svetlana 12AX7 re-issue, a very soft and sweet tube, very kind with your ears. Maybe one of the more even and balanced, together with the EH but, with an output level similar to the Mullard.
  • Electro-Harmonix 12AX7, very even and balanced and very linear, character similar to Svetlana but with way more output (maybe the one with the most) and, very crunchy when breaking up.
  • Sovtek 12AX7-WA, more or less same gain/output levels than a 5751 but, with a very sterile sound. It's being used by many makers, just because it's one with the less microphonics issues around and, it's cheap but, usually, this would be the very first tube to swap in your amp, if you have it stock.
  • Sovtek 12AX7-WB, practically the same has the WA but, with a tad more gain level.
So any of those above, could be a candidate for V1 and, which one to choose will be related to each particular application and taste.


Koch people says that they are currently loading there a Ruby 7025S or 12AX7A-C. That are Chinese tubes of high quality and sonically better than JJ ECC83S tubes.

For this position, everything is possible, once we got rid of noise and microphonics with the tube in V1.

My own experience with this particular amp says me that tubes with very even response, without any bump in any range of frequencies and, a good definition and harmonically rich content will work better here.

V3 (PI)

For this position, my natural election is always a Sovtek 12AX7-LPS with balanced triodes. But, another tube that can work equally well is a JJ ECC803S. Even a Chinese 12AX7A-C or a NOS 5751 can do a good job here.

Tests: Phase 1 - same tube in V1 and V2

Since both tubes work for every channel in his amp, best way to understand how each type of tube affect the voice and character of this amp is to mount same tube type in both positions. In that way, we can analyze how each particular tube works in every circumstance (low gain, high gain, break-up, clean, etc).

Therefore, in this first phase, I've tried to check how each tube type worked with the two styles I've choose: Blues/Hard Rock and Metal.
Results should help me to decide if a certain tube will work better in V1 or V2 and, if they would work better for Rock or Metal.
I've reduced the type of tubes for this test, because I've already rejected some other tubes in other tests, because of their sonic quality. These below were rejected:

  • (no brand) 7025 Grey Anode (probably Chinese, anodyne).
  • TAD 7025, Chinese, extreme high content, bonny and hollow low end.
  • TAD 7025-WA, similar to Sovtek 12AX7-WA, better sonically, anyway.
  • TAD 12AY7, voice and character differs a lot respect of any 12AX7 tube.
  • EH 12AY7, same case as previous one.
  • Sovtek 12AX7-WA, I didn't liked it in any amp.
  • JAN/Philips 5751 NOS: I've got just a single tube so, not valid for this test.
I'm gonna paste here the notes I was taking while testing every tube type, in both styles, Rock and Metal.
For each style, I've tried the three channels. Clean corresponds to Clean channel. Crunch corresponds to OD channel and, Gain corresponds to OD+ channel.

Settings for each style/mode corresponds to the sample settings that you will find in your user's manual.

TAD 12AX7A-C (Shughuang, China)


Nice body. Warm, defined. No noise, feedback or squealing.

Sharp and thin Mids. A bit compressed but defined.

Compressed but crunchy at same time. Not bad. More for Metal than for Rock but, overall, well sounding and standing the definition. Feedback in sound tails but, controllable muting strings.
High white noise level.


Trebly, thin and hollow. No noise.

Thin, sharp and crunch. With snappy trebles.

Nice for chugs. Thin, crunchy and dark sound, with sharp high end and a tad undefined low end.

TAD 7025 Highgrade


More defined than previous one. Sound is more trebly, even piercing. Higher gain. Thin, without body low end.

Crunchy, defined but piercing. Some lack of sustain and some principles of feedback.

Best mode of three. Nice crunch, maintains definition note-to-note. A tad bright but, cuts the mix with attitude. Feedback in tails of sounds, controllable muting strings.


Clean, defined, sterile and bright. More gain and definition than the previous tube.

Cuts the mix less than previous one. Crunchy, defined but a tad hollow. No feedback.

Better than the previous tube. Low end is clearer and defined. Nice chugs and very Metal sound. Better pinch harmonics. Lower feedback at the very tail of the sound, controllable muting strings.

Sovtek 12AX7-WC


No noise. Well balanced, nice body and definition, slightly warm.

Breaks up before the previous ones. Nice sustain. Light feedback. Crunchy and slightly compressed. Tends to Mid-Trebles.

Feedback in tails but controllable muting strings. Excellent sound, well defined and very Rock.


No noise. Well defined and better than previous tubes. Less hollow. Cold but, not bad.

Defined. Hollow Mids, slightly thin sound. No feedback.

Very defined. Better than previous tubes. Less chugs. Nice distortion but, more crunchy than creamy. Better for Rock than Metal.

Svetlana 12AX7


No noise. Perfectly balanced and crystalline. Very kind to the ear but, with a slight bump in Mid-Trebles.

Crystalline, well defined. Nice Mid-trebles that help to cut the mix. Nice sound, good for Rock, without extreme EQ, very even.

Excellent Hard Rock sound. Powerful basses, crystalline definition, crunchy and very kind to ear.
Starts feedback before previous ones but, it can be easily controlled by muting strings.


No noise. Perfectly balanced. Richer sounding than previous ones. Tasty Mid-trebles. High end well represented without going piercing. Clean, crystalline, angelical. Very sweet sound.

Mids are a tad hollow but, better definition than in previous ones. Nice legato in riffs.

What a Metal tube!. Excellent definition. Excellent chugs. Always defined. Excellent transconductancy, allows speedy riffs, with outstanding definition note-to-note. Excellent sustain and light feedback at the very tail of sound.



Louder than Svetlana. EQ more exaggerated than in Svetlana, bigger body but less definition. Nice sound, overall.

Tends to more pronounced trebles than Svetlana and, sound more compressed.

Big volume step when changing channel. Powerfuller than the Svetlana but less defined and a tad more aggressive to the ear.


Not so defined as the Svetlana but, nice body and warmer. It should have lot of Mids, that doesn't seem to disappear when you switch down Mid Shift and, with Mids knob at -5.

Tends to Mid-Highs. Slightly thin but less than rest of previous tubes.

Volume increase when changing channel not so high as in Rock mode. Way less definition note-to-note than the Svetlana. Powerful sound, dark and a bit confused with excessive Mid-Lows. Excellent chugs but, not defined enough for shredding works but, it has a nice legato anyway. Lacks a bit of sustain and the feedback comes very late but very strong, even that is controllable.

Electro-Harmonix 12AX7


So defined and balanced as the Svetlana but WAY MORE gain than previous ones. Excellent definition and dimensionality. Tends to Mid-Highs.

No noise. Excellent crunch, very powerful, defined and very Marshalish. Mid-Highs very notable.

Brutal!. Hard Rock in pure state. LOT of gain. Excellent, in the right spot. A great tube for Hard Rock. Nice sustain but strong feedback in tails.


As grateful as the Svetlana but with all the strength (and more) than the JJ. No noise.

Hollow mids, as all tubes. Better gain and strong Mid-Highs.

Perfect Metal tube!. Excellent chugs, dark but defined low end, bright high end but not piercing, nice body, excellent sustain, good transconductancy that allows speedy riffs. Creamy and crunchy at same time. Feedback late in tails, controllable.

Tung Sol 12AX7 RI


Clear sound but a tad exaggerated in EQ. Not so pure or balanced as the Svetlana or EH. It has the gain of the EH, with powerful basses and sharp Mid-Highs.

Tends to Mid-Highs. Nice crunch, very sharp and, maybe a tad piercing.

Powerful, very Rock. Nice sustain. Feedback late in tails, controllable. No excessive noise. Good definition note-to-note, a tad veiled respect of Svetlana or EH, closer to JJ.


A tad sharp but, nice body and sound, overall.

Its powerful basses help this tube to sound less hollow than rest of tubes.

Basses help to generate powerful chugs but, still with a good note-to-note definition. Mids sound a tad confusing. More for Rock than Metal.

Mullard 12AX7 RI


Beautiful sound, full of harmonics, with sharp Mid-Highs but not piercing. Good gain level, less than EH and closer to JJ but, more than Svetlana.

Excellent. Cutting Mids. Distortion with tasteful crunch and very defined. Very British sounding. Spatially, the sound is wider and bigger and, "smells to full stack".

Awesome, Incredible!. Rock Stadium sound. Sharp Mid-Highs, slightly piercing but, very musical.
Perfect definition, 3D sounding and nice harmonics. Nice sustain , with light feedback late in tails.


Beautiful sound, angelical. Pure, with a nice body. A bit thinner than in Rock style but, one of the  best of Metal style.

Nice crunch and excellent definition. A tad sharp and bright for Metal but, good enough.

Excellent!, I have no adjectives. Incredible pinch harmonics. Practically no feedback.

TAD 7025-S Highgrade


Very low noise level. Excellent sound. Warmer and more body than the Mullard. Less spatially open but, equally harmonically rich.

Nice crunch, not so sharp as the Mullard. Less legato.

Nice sound. More exaggerated in lows and highs than Mullard, closer to the Tung Sol. Less sustain than in the Mullard.


Warm sound, like Tung Sol, more or less. Not so pure as the Svetlana, EH or Mullard.

Hollow, less convincing than the Mullard or Tung Sol.

Very good. Darker than Mullard. Nice definition. Low end a bit veiled. More for Metal than Rock. Easy Pinch Harmonics but, without the bite of the Mullard, softer. Acceptable sustain but lower than in the Mullard. Feedback in tails.

Tests: Phase 2 - the 3 finalists

Of all those tested tubes, the one that more likes me is the Mullard reissue (as usual). It seems able to work in any style, any mode, with a delicious harmonics content and a big spatial openness. The drawback is that it has a gain level a tad higher than what I actually need.

The EH once more showed its incredible versatility and, even that is poorer in harmonics and, more mono dimensional than the Mullard, its sound perfectly suits every style and mode in this amp.
Drawback is that its gainer than the Mullard.

The Svetlana was a nice surprise. Has the lower gain of those three but, it has a very balanced sound, smooth and kind to the ear and, seemed as versatile as the other two. Pushed hard works better for Metal than the EH or the Mullard.

Sonically, those are the three that I would choose for this amp but, to have better information, I need to check those with more volume/gain ranges, to see which one works better at low volume (with full body, definition and rich) and, which one works better at high volume (less feedback, more definition, sustain).

Svetlana 12AX7


Very decent from 7:00h but, it starts to sound really good around 9:00h. The sound is beautiful, silky.
Starts to break up around 10:00h, with a sound a la "Little Wing".
Between 10:00 and 11:00h sounds very bluesy.
Beyond 1:00h, better to use the OD channel but, it stands very linear even with volume at max.
While increasing the volume, the sound sharpers every time more, loosing its silky character.

Not so good at low volume, starting to sound decently around 9:00h.
Good sound around 10:00h.
At 11:00h, feedback in tails and Mid-Highs sharpen a lot.
At 1:00h Mid-Highs are more tamed and the sound is really nice but, feedback starts early an strongly, even that you can still control it by muting strings.
At 3:00h the sound is really good but, feedback starts really soon, is strong and difficult to control.
Overall, very linear but, tends to go sharper in Mid-Highs with more volume.
Better results with  more gain and less volume, overall.
Snappy basses at high volume seem to mean that the power stage is overflowed or that the speaker isn't able to handle that energy.

Starts to sound decently at 9:00h.
Around 10:00 sounds very nice. Low end a bit thin and crunchy. Impressive pinch harmonics. Nice sustain. Feedback in tails, not so soon not late, controllable. High noise level.
Around 11:00h, the sound is powerful but the power tubes start to be saturated enough and the distortion doesn't sound as grateful.
It maintains a good definition always.
Starting at 1:00, early and strong feedback, without control.
Beyond 2:00h unusable, excessive squealing.
Overall, it seems that this tube, by itself, supports well gain and volume but, everything goes wrong in the power stage, when pushed really hard.


Starts to sound decently around 7:00h, colder and sharper than in Rock.
At 9:00h, it sounds better, warmer and with more body.
At 10:00, slight break up, with a wonderful sound, angelical.
Starting at 11:00h, the sound goes sharper and, basses sound a tad hollow and the sound seems doubled.

Sounds decently starting at 7:00h.
Good around 9:00h.
Impressive around 10:00h. Clearly, at this position is where you get the best of this tube.
Basses start to go hollow beginning at 11:00 but, without feedback.
Very Metal at 10:00h!!!.

Very decent really early.
At 9:00h sounds really good, late feedback in tails, controllable.
Beyond 11:00, feedback starts as soon as you leave some open string.
At high volumes, it seems as if the amp or speaker were going to explode. Excessive gain.

It seems that the sweet spot for this tube is between 9:00 and 10:00h of the volume knob of this amp. It's where you will get the best of this tube. Beyond 11:00h, to much gain enters in the power stage and, the distortion goes uglier.
Fortunately for that range you have a nice volume level, not low not high, easy to work.
At 9:00h the loudness is very acceptable.
At 10:00h it starts to be high but, without hurting your ears.
At 11:00h is excessive and the power stage seem to not being able to handle it.
I love the silky character of the cleans of this tube, very angelical but with the right amount of warmth and body. The crunch in Metal is really awesome.

EH 12AX7


Acceptable at 7:00 and good at 9:00.
The right spot is around 10:00h.
Not so silky as the Svetlana, sharper but nicely sounding.
Breaks up at 11:00, later than the Svetlana and, on this spot the harmonics content is highly increased.
At 2:00h has more or less same break up level than at 11:00h but, way more volume. So, it stands defined very well.

Decent beyond 7:00h.
A bit hollow and sharp around 9:00h.
At 10:00 sounds better but, still not in its sweet spot.
At 11:00h seems the sweet spot but, sounds brighter and sharper than the Svetlana and, maybe too much gain for the power stage.

Acceptable at 7:00, but very sharp.
At 9:00h sounds better. Light feedback with open strings.
At 10:00h strong, nice legato and sustain. Easy feedback. Overall, sharp and bright, compared to Svetlana.
The sweet spot of this tube seems to be at 11:00h, the sound of this tube at this spot is incredible good for Rock but, it seem to feed the power stage too much.


Decent at 7:00h but, a tad thin and sharp.
At 9:00h, it starts to sound good but, with less quality than the Svetlana. Its sharp highs give it some coldness, compared to the Svetlana.
At 10:00h the harmonics start to shine but, still very sharp.
At 11:00h is the sweet spot for this tube.

At 7:00h very convincing but, a bit hollow.
At 9:00h still sharp but, with good legato and nice pinch harmonics.
At 10:00h more power, still sharp. No feedback issues.
At 11:00h the right spot, nice sound, very metal, clean and defined but, a tad bright.

At 7:00h workable sound.
At 9:00h sounds very good, no feedback issues.
At 10:00h too much gain and, the power stage has a bad distortion. Excessive squealing.

The good range for this tube seems to be between the 10:00h and 11:00h but, closer to 11:00h. At this time, the signal level is so high that the power stage starts to distort in a bad way and there is an excessive squealing.
For this particular amp, this tube doesn't seems the best election but, this is probably because the power tubes it currently has that, when they break up, I don't like their distortion character.

Mullard 12AX7 RI


At 7:00h, workable sound. No noise.
At 9:00h starts to sound really good, with the warmth and richness of the Svetlana but more bright and bite.
At 10:00h, light break up, delicious, slightly bluesy.
At 11:00h, completely breaks up, delicious crunch. Clear and defined. The power stage starts to be overloaded.
Increasing more the volume, the break up level remains the same but, the content increases in harmonics and goes louder but, without loosing definition, never. Excellent, without the excessive highs of the EH.

At 7:00 usable but, not on its best.
At 9:00 better, but still not on its best.
At 10:00 delivers an impressive crunch, very British.
At 11:00h seems on its sweet spot. Incredible crunch that surrounds you. VERY LOUD.
Increasing the volume, squealing and the sensation that the power stage or the speaker cannot handle so much gain but, the tube itself continues delivering a sound that goes every time better!. Very strange!.

At 7:00h, useful sound but a tad dark.
At 9:00h totally useful, with infinite sustain. The sound is way open than at 7:00 and feedback late in tails.
At 10:00h, pure Rock Stadium sound. Feedback enters with open strings.
At 11:00h, you should hear it to believe it. IN-CRE-DI-BLE. Strong feedback with open strings. Awesome pinch harmonics.


At 7:00h, crystalline clear. Less warmth than Svetlana (that sounds really sweet in this mode) and, less sharp and bright than the EH. Not on its best.
At 9:00, the openness is better than in Svetlana but, it sound sharper.
At 10:00h, close to its sweet spot but, basses are still a bit sharp.
At 11:00h sweet spot. Slight break up than reveals the nice harmonics of this tube.
Overall, the Svetlana sounds silkier and more balanced but, the Mullard seems to better cut the mix and, the unwanted highs can be rolled off with the amp controls.
Beyond 1:00h the power amp or speaker seems unable to handle so much gain.

At 7:00h usable sound but, still not on its best.
At 9:00h usable sound, good sustain, nice pinch harmonics and good chugs at a reasonable loudness.
At 10:00h AWESOME. Fantastic chugs, pinch harmonics, superlative definition. Powerful... it has it everything!.
At 11:00h you SHOULD experience it. The sound is incredible but, feedback starts really early and, we are still limited by the power stage or speaker.

At 7:00h totally usable at low volume.
At 9:00 usable, infinite sustain and slight feedback on tails.
At 10:00h excellent sound but, power stage and/or speaker are in trouble to handle so much gain.
Beyond 11:00h, impossible to play. Excessive squealing, even with muted strings.

The Mullard is a very linear tube and delivers good results in every mode. This tube shines specially when you can push it beyond its break up spot, where it can bring you delicious harmonics. The sound character is between the Svetlana, more silky and, the EH, sharper and brighter. But no other tube sounds as 3D as this one (only the NOS Philips 5751 seems to sound slightly more spatially open).
When this tube on its sweet spot is able to push the power tube to its respective sweet spot, the sum of harmonics deliver a sound that is simply spectacular. I have no adjectives, you should experience it to understand it.

Weighting the 3 finalists tubes

These three tubes will work really good in this amp. All them are able to maintain a high note-to-note definition, during most of the gain and volume range.
From those three, the more balanced, sweet and silky sound comes from the Svetlana (nice discovering!). It also seems to break up a bit earlier, so you can extract its harmonic juice at lower volumes.
Harmonically rich and very even EQ'd, with smooth trebles / Mid-Highs and, very crystalline.
When it breaks up, isn't so crunchy as the Mullard or EH but, its distortion grain makes it specially good for Metal, where its greater compression and creamy distortion seems to better suit this amp.
Also, in style metal and clean mode, its warm Mids help to avoid this tube to sound sharp or hollow when recessing Mids.

The EH is probably the tube that more electrons injects in the power stage, giving an earlier break up to power tubes and, producing feedback and squealing at lower volume settings, what makes it difficult to get the best from this tube.
From all three, this one is the brighter and sharper one. It's Mid-Highs give it of an excellent crunch but, it can sound a bit piercing, when you start to rise the volume.
In Metal / clean, sounds a tad bright and sharp but, maybe will be what you need for a darker amp and drop tunings, where it could help to balance excessive low end.
It's a great tube for other power tubes that can handle its high output and gain.

The Mullard RI is, plainly, awesome. It hasn't the silkiness of the Svetlana and, its Mid-Highs are more notable than in the Svetlana but, less than in the EH.
Harmonically very rich and, it goes better the more you push it.
Very linear sounding and consistent among the whole range of gain / volume but, specially good between 10:00 and 11:00h, when we start breaking up the power amp, summing together power and pre-amp harmonics, where the is "from out of this world".
Main drawback is similar to the one with EH, at this gain / volume levels, the power stage or speaker seem not able to handle the excessive power.
Probably, more useful for Rock than Metal but, don't go wrong, it has fantastic pinch harmonics, chugs and palm mutings, also.

Before deciding which power tubes I will use for this amp, my current bet is the Mullard RI for V1 and V2, because my own style is closer to Hard Rock than to Metal but... that silky cleans of the Svetlana made me fall in love of that tube. Maybe, I will try mixing both. Let see.
Price difference is important here. The Svetlana goes around 19.4 Eur, while the Mullard is 25 Eur. So, the Svetlana seems a good candidate to stock but, Mullard production seems to be more consistent.
If you find the Mullard RI a tad sharp, try that Svetlana!.

Tests: Phase 3 - choosing power tubes

During my pre-amp tests, it was clear to me that the issues I was having with excessive feedback and squealing where less related to pre-amp tubes and more related to power tubes.
This amp is currently using a pair of matched JJ EL84, with Perfect Pair #6 (according to TAD matching system).
Originally, this amp came stock with Sovtek EL84M, a very sturdy tube but very sterile sounding.
Koch people confirmed me that they still think that those EL84M are the best power tubes for this particular amp but, since they are hard to find, they are currently mounting JJ EL84 tubes.
I've ordered three pair of tubes to check which one will better suit my needs.
TAD people says that those EL84M never go beyond a Perfect Pair #4, what means a plate current significatively lower. So, probably, I am using tubes with more power than needed for this amp.

My current needs are: to lower a tad the overall loudness, being able to better push tubes at low volumes, while preserving a rich harmonic content and, low noise, microphonics, feedback and squealing.

A curious note here, in none of the settings that you will find in user's manual the volume knob will be set up beyond 10:00h, what in my own experience corresponds to the boundary of the amount of power that power tubes and / or speaker are able to handle in this amp.

With all that info and goals, let see how the different power tubes work in this amp.
For these tests, I will leave the Mullard RI in V1 and V2 and, the Sovtek 12AX7-LPS in V3.

EL84M/E84L (Perfect Pair #4)


Overall, very trebly. I had to roll off trebles a tad to accept the sound. They are very clean and crystalline sounding but, they lack some kind of warmth. The sound is a tad sterile.
At 7:00 usable sound but, lacks some body. I'm missing some kind of "glue" between notes.
At 9:00 usable sound but, still lacking some glue. Very pure and crystalline sound.
At 10:00 starts a light break up and the legato is being enhanced. Low end a bit thin but, overall, good sound.
At 11:00 blues-like break up. Better presence of low end but, starting to sound a tad confusing note-to-note.
At 1:00 very good in every sense. The loudness is really high here.
At 2:00 fantastic and tasteful crunch. Nice body but, now not clear anymore.
Overall, works fine in the whole range and, stands very clean up to around 1:30h. No feedback issues, even at 3:00h (but crunch is excessive then).

At 7:00h usable.
At 9:00h usable, nice crunch.
At 10:00h usable but the sound is a tad hollow and thin.
At 11:00h is close to its sweet spot. Very loud right now. Still a bit hollow and, some feedback and squealing starts to appear.
At 1:00 sound much better, more body. Enough feedback and squealing.
Beyond 2:00 squeals as a pig, unusable.

At 7:00 usable.
At 9:00 usable.
At 10:00h nice Rock sound. Good power chords but, lacking some glue between notes.
At 11:00 Excellent Rock sound, still a tad thin in low end but, cutting really good. Feedback on tails. Power chords sound awesome.
At 1:00h awesome sound but, very loud and with high squealing, even with guitar's volume closed.

It seems to perform better between 11:00 and 1:00h but, the loudness level is very high in that range.


At 7:00 usable but very cold.
At 9:00 a bit better.
At 10:00 slight break up, the sound goes sharper.
At 11:00 better body, more break up but, better sound overall, with richer harmonics content.
At 1:00 more crunchy and warmth. It seems to sound better when you can get its harmonics out.
At 2:00 not very useful, confusing low end. The speaker doesn't seem able to handle those.

At 7:00 usable but, without body, sharp low end.
At 9:00 very usable, still lacking some strength in low end but, sounds way better but, still a bit sharp.
At 10:00 very Metal, maybe with some lack of body. The distortion grain is very adequate.
At 11:00 full, nice Metal sound.
At 1:00 excessive distortion but, surprisingly no squealing.

At 7:00 perfectly usable.
At 9:00 very good, just a bit more is needed.
At 10:00 starts to squeal with muted strings and the guitar's volume off. Once you get feedback, you can only remove it switching to clean channel.
To use a Noise Gate for this mode is a must.

A tube better for Metal than Rock. It has a late break up and seems a bit cold with low gain, lacking some harmonics and dimension. Very sterile or Hi-Fi.
It works better when pushed hard, when requires high loudness.
The distortion type seems better for Metal than Rock.
It has a lot of high end or Mid-Highs (but not piercing) and some recessed Mid-Lows.
Low end sound a bit thin, sharp and confusing but, high end is always good represented.

Sovtek EL4 (Perfect Pair #6)


At 7:00 usable. Warmer than the EL84M, with better glue between notes.
At 9:00 very good. Well balanced. It doesn't seem to be enhance no frequency range in particular. Slightly warmer and darker than the EL84M. Very quiet.
At 10:00 sounds beautiful, very silky. Slight break up but lower than in EL84M. No noise.
At 11:00 more break up, looses a bit of definition in low end, that goes a bit hollow. No noise. Excellent Mids and Highs.
At 1:00 Bluesy break up. Excellent Mids and Highs. Low end a tad poor but usable.
At 2:00 too much crunch. Looses definition in chords.
Overall, it sounds good along the whole range.

At 7:00 usable but, a bit fuzzy.
At 9:00, more or less same as at 7:00 but louder.
At 10:00 better but, still lacks some body. A tad sharp and hollow.
At 11:00 close to its sweet spot but still not breaking up enough. Way better body than the EL84M.
At 1:00 the tube seems to get too much from the amp. Some rings and noise.
Overall, it lacks some distortion. Better legato than in EL84M, from the beginning. Good Mids and decent lows and highs.

At 7:00 very usable. Nice sustain. No feedback.
At 9:00 very usable. Feedback late in tails, controllable.
At 10:00 sounds very nice, good body, good definition, good sustains, late feedback in tails, controllable.
At 11:00 powerful. Less body, nice definition, excellent pinch harmonics. Early feedback but, still controllable.
At 1:00 very powerful sound, maintaining definition. Loud. Nice pinch harmonics. Shows some inner noises because of excess of vibration. Early feedback but, controllable.


At 7:00 very sharp and hollow.
At 9:00 a bit better, still very sharp.
At 10:00 very good. Warmer than EL84M, with better body. Silky sound, a tad sharp in Mid-Highs.
At 11:00 slight break up, sharpening Mid-Highs.
At 1:00 still nice high end but, too much break up and, chord definition is compromised.

At 7:00 usable but sharp and hollow.
At 9:00 better but, still lacking some body.
At 10:00 close to its sweet spot. A tad bright and sharp for Metal. Nice chugs.
At 11:00 Perfect!. It's sweet spot.
At 1:00 everything is being exaggerated, excessive gain.

At 7:00 totally usable, nice sustain.
At 9:00 same as 7:00, louder.
At 10:00 nice Metal sound. Nice chugs, pinch harmonics and eternal sustain. A bit undefined note-to-note.

Not being the best tube in nothing, is overall good for everything.
Breaks up later than EL84M, which makes you to rise the volume to get some harmonics from that tube but, even this, it has a better body and is warmer than the EL84M at low volumes so, is more versatile in the whole range.

Electro-Harmonix EL84 (Perfect Pair #6)


At 7:00 usable. Warm, soft and silky.
At 9:00 very usable. Warmer than previous ones. Slight roll off in high end, nice harmonic content and good 3D representation.
At 10:00 Perfect. Balanced, clean, defined, smooth, warm. No noise.
At 11:00 break up spot. Adding harmonics, beautiful sound. No noise.
At 1:00 too much break up. Good sound but not so clear, even that still defined.

At 7:00 usable. More body and warmth than previous ones.
At 9:00 totally usable. Well defined, a tad dark, nice crunch.
At 10:00 excellent crunch. A tad dark, what makes me to doubt if it will be able to cut the mix but, the distortion character is awesome and stands very defined.
At 11:00 very loud. Nice crunch. A bit more open than in the previous position but, I still have doubts about if it will cut the mix. Slight feedback, controllable.
At 1:00 same as in previous position but, louder and with an earlier feedback.

At 7:00 usable. A tad dark and far away but, overall, good.
At 9:00 same as previous, louder.
At 10:00 very nice sound but, a tad far away, as recessed, mono dimensional, veiled, without jumping out of the speaker.
At 11:00 very nice sound also, same considerations as in previous one.
At 1:00 more presence in sound. Excessive volume, early feedback but, still controllable.

Overall, this tube sounds very tasteful. Probably the sound closer to what you could expect from an EL84 but, the drawback is that this tube seems to lack some presence, dimension, and life enough to jump out of the speaker. It's a mess to see how the sound seems to come from the backside of the cab instead of from the front of the speaker and, it seems it will have some issues to cut the mix.


At 7:00 more or less same as the Sovtek but, with a more silky high end.
At 9:00 usable, warmer.
At 10:00 usable, not so pure in tone as the Sovtek but better body than previous ones.
At 11:00 slight break up. Sharper high end and, less defined.
At 1:00 higher break up, with similar characteristics.

At 7:00 usable, but sounding far away.
At 9:00 usable, but sounding far away and a tad dark.
At 10:00 nice Metal sound, nice chugs, nice definition, still sounding far away.
At 11:00 seems the sweet spot for this tube, that sounds far away until it reaches this spot.

At 7:00 perfectly usable, still sounding far away.
At 9:00 very usable, very Metal. Still far away. No controllable feedback.
At 10:00 very Metal, still far away.
At 11:00 better sound overall but, if you get feedback, you can only control it by switching to clean channel.

From these three tubes, is the one with the best definition. Smooth highs and Mids and a bit bumped Mid-Lows, what makes it darker.
Its sweet spot is around 11:00 but, it seems to need lot of current to be excited. Probably, better results when using boosters or overdrives.
Sonically very smooth and silky, always sounds far away, as coming from the back side of the cab, what can make it difficult to cut the mix.
It can be very useful to tame excessively bright amps.
Mixed feelings with this tube, because it has a really tasteful sound but, it cannot be projected jumping out of the speakers. If it was able to do that, it would be my preferred tube, all the way.

JJ EL84 (Perfect Pair #6)


At 7:00 very usable. Nice body and warmth. Smooth high end.
At 9:00 very good. Nice harmonics but, tends to Mid-Lows.
At 10:00 slight break up. Nice sound, warm and jumping out of speaker. Very dynamic. Loudness is now high.
At 11:00 bluesy break up. Starting here, the distortion grain of this tube I don't like it, sounds rude to my ears.
At 1:00 more or less the same than previous position but way louder.
At 2:00 more distortion, louder.
It seems a good tube to have a nice headroom. Breaks up late, defined, warm and jumps out of the speaker. Very gainy and very linear, until it breaks up.

At 7:00 usable. Way better than previous tubes. Sound a bit dirty, because of lack of volume.
At 9:00 very usable. Still lacks some volume.
At 10:00 good volume but seems to have too much of high end and recessed mids, to have the right crunch.
At 11:00 sound goes overall better, fuller but, we have early feedback but, still controllable. Piercing highs and, a tad exaggerated low end.

At 7:00 usable.
At 9:00 as in 7:00, a tad veiled in low end, very usable at a volume kind with your ears.
At 10:00 awesome!. Pure Hard Rock. It's in its sweet spot, delivering an excellent sound and harmonics content. Powerful basses, piercing highs. No feedback issues.
At 11:00 like in 10:00 but, in industrial quantities. Very loud. Earlier feedback. Its excessive low end seems to compromise the ability of the speaker to represent them and, make the sound a bit confusing. Excellent pinch harmonics and very snappy and piercing highs.

Excellent tube, full of life. It makes this combo to sound like a Full Stack.
Between 10:00 and 11:00 you should experience its loudness to understand how powerful can go, the sound is massive. But, anyway, it allows you to have a nice sound at lower volumes, because it works very linearly but, in the commented range, is a demolition machine.
Excellent for Hard Rock, not so good for Blues or crunch.


At 7:00, a bit thin (lacks some mids). Witch excess in low and high end, dirtier than previous tubes.
At 9:00 more or less the same, louder and a bit more body.
At 10:00 way better but, highs are really piercing and hurt the ear.
At 11:00 better high end, more body. I don't like how it breaks for Metal stuff.

At 7:00 usable but, it lacks I-don't-know-what.
At 9:00 usable. Low volume with nice chugs, pinch harmonics. No feedback issues.
Ar 10:00 very good. Nice chugs, accurate and cutting power chords, nice pinch harmonics. No feedback.
At 11:00 awesome!. Super Metal. Feedback starts and some unwanted squealing. Monstrous loudness. Noise Gate is a must.

At 7:00 totally usable. Lacks some power in low end but, everything else is there.
At 9:00 Fantastic. Nice Metal at low volumes.
At 10:00 Excellent. Drawback is that is feedback starts, you can only remove it by switching to clean channel.
At 11:00 more power than this speaker can handle. Feedback is a real issue now.

It behaves very well along the whole range of volume but, its wild face starts between 10:00 and 11:00h, where it develops a brutal power, with strong low end, piercing trebles and an overall sensation of power that are impressive. Very good for Hard Rock and Metal.
Noise Gate with high gain/volume is a must.
You should experience this tube at high volume and gain to sense its power.
You will not like to stop playing (your neighbors and Police, yes).

TAD EL84-STR (Perfect Pair #6)


At 7:00 usable, very similar to JJ.
At 9:00 very usable. Maybe smoother high end than JJ and fuller Mids.
At 10:00 slight break up. Overall, smoother high end than in JJ, warmer Mids, without so much projecting outside the speaker. Nice tube, more defined than the JJ.
At 11:00 Low end more exaggerated than in JJ. Breaks up more bluesy and I like it more than JJ but, the excess of basses veils a tad the overall sound.
At 1:00 like in previous position, louder and with more distortion.

At 7:00 usable, a tad dark.
At 9:00 very usable. Lacks some strength but it has a better break up than the JJ.
At 10:00 very good. Loud and it has more Mids and Lows than the JJ, with smoother trebles. Less 3D projection than the JJ but, more than the Sovtek or the EH.
At 11:00 same remarks as previous position. The excessive basses make the combo to vibrate to much and, some noise appears in tubes because of this.

At 7:00 usable, lacks some sustain.
At 9:00 totally usable. Light feedback on tails, controllable. Excessive Low End, can work to tame bright amps.
At 10:00 sounds very good but, not so alive and powerful as the JJ. Excessive basses.
At 11:00 very powerful. Low end kicks impressively. The sweet spot. Excellent sustain, pinch harmonics more clear than in JJ. Earlier feedback. Controllable.


At 7:00 usable. Less sharp and thin than the JJ.
At 9:00 totally usable. High end less sharp than in JJ, full sound, clearer and with good body.
At 10:00 sharp clean, less harmonic content than the JJ.
At 11:00 more body, more break up, sharp. Crystalliner than the JJ and, it breaks up more nicely than the JJ, to my taste.
At 1:00 sounds a tad like a Fender pushed hard, more crystalline than sharp. Lot of low end, good mids and, smoother high end.
At 7:00 usable. A bit far away and lacks some strength.
At 9:00 very usable. Nice chugs at low volume but, still lacks some body.
At 10:00 very well. Very Metal. Nice Chugs, good sustain, good basses. Impressive Power Chords. If feedback, you can only remove it by changing the channel. Noise Gate is a must.
At 11:00 wonderful. Super Metal. Those powerful basses give lot of strength to chugs. Pinch harmonics less powerful than in JJ. If you get feedback, it can be controlled by changing channel.
At 7:00 usable but, a bit far away.
At 9:00 very usable at low volume. Darker than JJ, smoother high end than JJ.
At 10;00 Squeals from the very beginning. Noise Gate is a must. Excellent Metal sound. Powerful basses, well defined high end, no stridency, nice pinch harmonics.
At 11:00 Perfect Metal. Squeals even before giving a simple note. Noise Gate is a must. Excellent chugs, powerful basses, controlled trebles, nice pinch harmonics but smothers than in JJ.

As in the case of the JJ, this tube delivers its best between 10:00 and 11:00 in this amp.
Better crunch and works better for Blues than the JJ, while the JJ suits better Hard Rock.
In Metal mode, they are very similar but, the TAD has more controlled trebles, fuller mids and deeper basses and, everything without loosing definition.
Harmonically, the JJ is richer and has a better 3D projection (jumps out of the speaker in a wider beam).
Works exceptionally good for Metal and, it can help to balance amps with weak basses and bright trebles.

Mullard EL84 re-issue (Perfect Pair #6)


At 7:00 usable. Clean and transparent as the EL84M but darker, in the ballpark of the TAD or JJ, in between both.
At 9:00 very pure but not cold as the EL84M. Smooth high end as in the TAD, small bump in mids but not so much as in the TAD. Slight break up that sounds really tasteful. No noise. Extremely quiet.
At 10:00 light break up. Very pure tone but not cold. Perfect definition and, its harmonics start to appear, with a quite well angelical sound.
At 11:00 Bluesy break up. Still maintaining an excellent definition. Loudness slightly lower than the TAD (better for my goals). Tasteful distortion. Nice body and excellent definition in mids and highs.
At 1:00 Excellent. Continues super quiet. Fantastic crunch. Very defined, no stridency. Excellent frequentially, nice body and super dynamic.

At 7:00 very usable. Nice crunch at barely dorm levels. Not so far away sounding as other tubes. Super quiet.
At 9:00 very usable. More or less same as previous position. Still very quiet.
At 10:00 Excellent crunch. Slight feedback at tails, controllable. Very British. To play and play and play.
At 11:00 Awesome. Excellent sustain and legato. Awesome definition. Its sweet spot, no doubt. Compared to JJ and TAD, it sounds at lower volume.
At 1:00 Just incredible!. It has some kind of glue that links together the notes with an unusual richness. Very dynamic. Always defined. Very low noise level. The best distortion character of all these tubes. Excellent transconductancy, allows speedy riffs and never looses definition.

At 7:00 very usable. Nice sustain. Nice Hard rock sound at low volume. Very quiet.
At 9:00 very usable. Better sustain and, slight feedback on tails, controllable. Still quiet.
At 10:00 without the brutal power of the JJ, with the smooth highs of the TAD and a delicious body. Defined and with sustain. Earlier feedback but, controllable.
At 11:00 spectacular!. Hard Rock in pure state. Infinite sustain, nice dynamics. Lot of strength but, always controlled and defined (differently to JJ).


At 7:00 sounds silky, slight break up, smooth highs. Very good.
At 9:00 warm, without sharpness. Very good.
At 10:00 Excellent. Angelical. Delicious.
At 11:00 Impressive. Highs snap with crystal bits, without hurting. Very warm and defined, with excellent representation of low end, mids and highs. Powerful sound. Still very quiet.
At 1:00 Excessive volume and, too much distortion for cleans. But, still sounds awesome.
At 7:00 very usable.
At 9:00 very usable. Some rings, due to vibration.
At 10:00 excellent crunch. Nice chugs but, less compressed than needed for Metal.
At 11:00 Impressive. Still defined and pushing really hard. Awesome chugs and, always controlled.
At 1:00 Brutal. It seems that nothing can make this tube to loose the focus, still defined. Danger of unwanted feedback. Noise Gate is a must.

At 7:00 totally usable, at dorm levels.
At 9:00 totally usable, reasonable volume. Barely infinite sustain. Excellent lows and definition.
At 10:00 sounds awesome but you get squeals even without touching the guitar. Noise Gate is a must.
At 11:00 Brutal!. What a tube!.
This tube seems to combine the best of the previous ones and to remove their main drawbacks.
At low levels is so crystalline as the EL84M but, without the coldness of this late.
It has a frequential balance similar to the EH or the Sovtek but, it has way better projection out of the speaker.
Not so loud as the JJ and slightly less than the TAD but, it works very linearly and, it never looses definition. At contrary, the more you push this tube, the richer the sound.
Works really nice between 10:00 and 11:00 but, at 1:00 is from other world. It's a mess that in this position the loudness is too much for my needs but... believe it, the sound is Brutal. You have to experience it.
Its linearity and frequential balance allows it to deliver a nice sound at any volume and gain levels, showing a distortion without excessive compression, without veiling basses and without sharpening highs too much.
Dimensionally, maybe the power of the JJ helps it to better be projected out of the speaker at lower volumes but, at 1:00 the JJ is very undefined, while the Mullard sounds at its best.
The distortion type suits better Blues, Hard Rock and Crunch. For Metal, I bet many people would prefer a more compressed and creamy distortion but, honestly, it works really good even for Metal.

And the Winner is...

No doubt. The Mullard reissue, hands down.

Very quiet, never looses the focus and stays always defined. Good in every mode and loudness level but, it sounds better when you harder push it. Very balanced, never looses body, even in extreme metal positions with recessed mids. Warm and not strident, nice presence in the range of frequencies that is natural to guitars. Very dynamic, allowing different break up levels depending on the strength of your picking.

Tests: Phase 4 - last touch

Without any doubt, this combination is a clear winner. Two Mullard RI in V1 and V2, a Sovtek-LPS in V3 and a couple of Mullard RI in power tubes give me the balance I was looking for. This combination doesn't shines specially in no mode but cover every one with attitude.
But, I felt in love with the Svetlana so, I wondered how would it work if I put an Svetlana in V1.

Testing Last alternative combination

V1: Svetlana 12AX7
V2: Mullard 12AX7 re-issue
V3: Sovtek 12AX7-LPS
POWER: Mullard EL84 re-issue

It's also a fantastic combination but, I was surprised.
The Mullard is smoother than the Svetlana!. The Svetlana seems to have a big bump in mid-highs that produce a very crystalline and sharp sound.
The Svetlana seems to be hard to distort, being very crystalline up to very low levels, what can be good for who is looking for more headroom and for, who has the possibility to play really loud.

Overall, that peak in mid-highs that the Svetlana has is the same as in the JJ EL84 and, maybe this is what makes them to better jump out of the speaker, cutting more the mix.
The Mullard EL84 is more balanced and lacks that peak in mid-highs so, it can sound a bit distant at low volumes (an issue that disappears at higher volumes).
The Svetlana paired with the Mullard EL84, helps to recover that peak in mid-highs and, therefore the sound jumps better out of the speaker and cuts better.

But, the Svetlana lacks the "glue" note-to-note that the Mullard RI has, until you push it really hard.
The sound goes sharper and crystallized, closer to American sound, to a clean Fender, with cutting high end and well represented lows. While the Mullard has a more British character, complexer, with some fuzzy harmonics and better legato.

In Rock or Blues mode, the resulting sound is monstrous when you reach killer volumes (at 1:00) but, I am still missing that "glue" that the Mullard has.

In Metal mode, that lack of "harmonics fuzz", makes it a more accurate sound, allowing cleans more Metal than with the Mullard. Sounds a tad colder than the Mullard but, it better suits this style.
Of course, at 1:00 the sound of this set of tubes is massive. The sound eats you, with strong basses, cutting highs and a big sensation of power.

Finally, I will leave that Mullard in V1, because allows me to achieve better results at lower volume but, I strongly recommend that Svetlana to whoever that can play really loud and, to whoever that could need a more cutting sound.
To pair an Svetlana with a JJ EL84 or any other very bright tube as the EL84M can be a mistake.

Respect of its distortion character, the Svetlana sounds more American, more compressed (but awesome!) than the Mullard, that has that British crunch and richness.

The Video

I am attaching here the video related to the test of the set of tubes that I've finally choose.
I am demoing both modes: Rock and Metal, in the 3 channels at different volumes.
I am sorry because of the Metal demo, I bet it will have no sense for Metalheads but, I hope they can focus in the sound, instead of my no sense riffs.


  1. Wow dude, this is great details. A fantastic read and info from you as always!

    1. Thanks a lot for your feedback!.
      All the best!.

  2. Impresionante trabajo! Estoy pensando en adquirir ese ampli. ¿Crees que da un buen sonido clásico tanto limpio como ligero overdrive para blues y rock'n'roll? Por el precio de ese ampli, tengo una opción a un Tweed deluxe (hecho a mano a partir de un kit Tube Amp Doctor con mejoras, tranformador de salida original de fender, valvulas RCA, y orange drops). Se que es menos versátil pero es el tipo de sonido clásico que me gusta. ¿Sabes algo de esos Tweed de kit?

    1. Gracias por tus comentarios.
      El limpio de este ampli es un tanto soso, ni Fender, ni Vox, ni Marshall, tal vez más cercano a Mesa que a cualquiera de los otros.
      Lo mejor de este ampli es su canal OD (Crunch), donde brilla espectacularmente.
      Pero, sinceramente, si estás pensando en un ampli sencillo con un excelente canal limpio, sobre el que esculpir tu propio tono con la ayuda de pedales, yo me iría por ese Tweed Deluxe.
      De hecho, yo estoy trabajando ahora con un Fender Hot Rod III Deville y, estoy encantado.

    2. Gracias a ti, acabo de ver el Koch classic se12 que se acerca más al sonido ese clásico que te comentaba que el studiotone, pero no se si 12 w se quedarán un poco cortos para tocar con mi banda. Solemos tocar en locales pequeños y a volúmenes bajos, con los amplis a pelo, solo voces y metales por la mesa. El otro guitarrista tiene uno de boutique de 22 w y va sobrado.

    3. Si tu otro guitarrista va sobrado con 22W, significa que vuestro bateria es suave, nada que ver con los hijos de Boham.
      En todo caso, 12W se te va a quedar corto.
      Normalmente, unos 30W es lo ideal para pequeños locales.
      12W no deja mucho headroom para limpios.

  3. Hi, you have executed an excellent valve review! I just read it. Interesting enough, I actually retubed my Koch Studiotone 20 W and my Studiotone XL 40 W Heads with more or less the same results. Here are my details/results:
    - Studiotone: V1/2: Mullard 12AX7 RI, V3: Gold-Lion 12AX7 balanced, V4/5: TAD EL84-STR; Box: Bogner 212CB (Celestion V30)
    - Studiotone XL: V1/2: EH 12AX7, V3: Gold-Lion 12AX7 balanced, V4-7: TAD EL84-ST; Box: Koch KCC-212 (Koch VG12-90 (Jensen)).
    I use mainly Gibson '59 Les Paul RI (CCs) with these Amps. The Studiotone is now very bluesy while the Studiotone XL is more "the Rocker". This was is intended.
    If I would mainly use Single Coils like Strats or Telies, I shurely use Mullard EL 84 instead of the TAD EL84. This is the final result of my test.
    I have tested many valves available from suppliers in Germany (tubeampdoctor and tube-town) and I confirm the sound results above. In V3 the Sovtek 12AX7-LPS is also working well, however, I prefer the Gold-Lion.

    Best regards from Germany
    Volker Lohweg

    1. Thanks a lot Volker for sharing your own experience with these amps.
      I bet this will be highly appreciated by any interested reader.

    2. WOW: Very nice of you to gather all this useful information and then to share it with everyone. If it is true that you reap what you sew then you my friend will have a very good life! Kudos to you..

  4. Awesome review and great detail! It helped a lot.
    I went fairly "mainstream" and put in a Mullard CV4004 / 12AX7 for position#1; 2 X Mullard 12AX7 / ECC83 and a matched pair of Genalex - Gold Lion GL-EL84. The amp is "reborn" with this setup and sounds great in the 9-11 range on all 3 channels, where I usually play.
    I also have a a pair of matched Mullard EL84 reissues that I'll try one of these days...


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