28 January 2013

Amps: retubing Marshall 1923C 85th Anniversary Combo (Part 2)


This is my first retubing project for my beloved Marshall 1923C 85th Anniversary Combo (based on DSL50) and, a continuation of the first entry related to this topic.
As explained in Part 1, I am still checking some other tubes for V1 to take a final decision about which tubes do it better for my own goals.

Remaining V1 tests

Test 4

This time, I went for a Tung Sol 12AX7 reissue for V1, maintaining rest of tubes as in Part 1 so, the configuration was like follows:

V1: Tung Sol 12AX7 reissue
V2: EH 12AY7
V3: Sovtek 12AX7-WC
V4: Sovtek 12AX7-LPS

In clean, what you notice immediately is that the Tung Sol is a very musical tube. It instantaneously gave some body to the sound and made neck pickup to sound really nice.
Overall, the tube shows a clear bump in basses and trebles that are very useful while under controlled gain but, that can be too much when the tube is kicked hard. Trebles can go piercing (not so much as with the TAD 7025 HG, but close) and basses can go really boomy. When basses are projected hard, the sound lacks note-by-note definition.

In crunch mode, the sound goes very alive and powerful, with stunning basses and piercing trebles. Overall sensation of power. Stacking pedals in this channels gives too much gain, big basses that make the tube to loss definition note-by-note. Has more gain than the Svetlana tube and, probably more than the TAD 7025-S HG.

Very mixed sensations with this tube. It sounds really alive and musical, while the gain is being controlled under a certain amount but, when it's kicked harder, sound goes confusing, with blurry definition note-by-note and, excessive projection of basses and trebles. Don't take pedals as well as the Svetlana tube, by example. The Svetlana sounded me more natural in crunch and high distortion modes but lacked some body in clean.
Maybe, all those flaws can be fixed with some EQ correction in the amp's tone stack but, this results are aligned with my extensive tests in other amps.

Test 5

Time for the good-for-everything and specially-good-for-nothing beloved EH 12AX7, a tube that does the right job in every amp, every position I've tried but, without being the best in nothing (neither the worst!).
So, configuration looked like:

V1: EH 12AX7
V2: EH 12AY7
V3: Sovtek 12AX7-WC
V4: Sovtek 12AX7-LPS

One of the things I love of this tube is the sound when overdriven. It has one of the most defined crunch sounds in new production tubes, with some rawness and, from time to time, it seems to have micro-explosions that give some electric-bolt character to the sound.

Overall, the EH sounds more even EQ'd than the Tung Sol, with defined basses but that can sound a tad bonny if you heard before the Tung Sol. Trebles are in same ballpark, more or less and can go piercing with the bridge pickup, without correcting the EQ. It seemed to me with slightly higher gain than the Tung Sol and more quieter in V1.

Cleans are as goods as with the Tung Sol but, basses can sound a tad bonny if you compare them against the Tung Sol ones, even that they are well represented and the overall sound is nice and musical. Takes pedals with ease and, there is way more definition note-by-note than in the case of the Tung Sol.

In the Ultra Gain / Gain 1 channel, alone delivers a nice crunch, with very musical and detailed content. Takes gain pedals better than the Tung Sol and, remains more defined note-by-note.
In both cases, both tubes can create a high amount of feedback when pushed hard stacking several gain pedals, while this was more controllable with the Svetlana.
While in the Tung Sol you can hear a blurry wall of sound when kicked hard, the EH maintains a better note-by-note definition.

No surprises here. The EH always delivers at least an usable sound. Not the best of tubes, always delivers a correct sound. A nice workhorse.

Test 6

Time for the JJ ECC83S, the tube that usually brings the "true Marshall" sound and, it's the natural election for Marshall amps (among other makers). I have a relabeled version of those tubes, under the name TAD 12AX7-CZ. Those are verified JJs (so, good ones).

Therefore, configuration looked like:

V1: TAD 12AX7-CZ
V2: EH 12AY7
V3: Sovtek 12AX7-WC
V4: Sovtek 12AX7-LPS

Another workhorse tube (and cheap!) that can work really good in every position but, that can go darker or brighter depending on the amp so, not so straight forward as the EH. Usually, it has a pronounced bump in mids-highs and can go piercing. Stands very clean and has an over-specifications output level that can drive hard complex amp front ends (the EH also). In some way, the Svetlana is a silkier (and with less output) take of the JJ ECC83S.

Well, the JJ seems to suit very well this amp. Overall more balanced than I've expected. More or less same foundational tone as the EH but, surprisingly more defined note-by-note (while usually happens the opposite). Basses are more or less like in the EH (so bonnier than the Tung Sol) but, they are more prominent when drived hard but, without loosing the definition note-by-note.
Trebles are a bit piercing in the clean channel but, hurt less in the gain channel. I am quite sure a right EQ can fix this issue.

In clean, the sound is very nice, same body as with the EH or the Tung Sol, less boomy basses and same highs, more or less. Slightly less musical than the Tung Sol, stands definer in every situation. When pushed hard delivers a nice crunch, in the same ballpark of the EH but, maintaining a better definition.
Quieter (less floor noise) in V1 than the other two and, gets pedals with ease in the clean channel and, a good amount of stacked gain in the gain channel (except for the fuzz and any combination with the fuzz, when it has to much gain to digest).
Less feedback and more controllable than in the case of the EH or the Tung Sol so, easy to work with stacked pedals in both channels.

I am surprised with this tube . I usually didn't liked in the amps I've tested it before, at least as the V1 tube but, I have to recognize that is doing a good job in this amp and with the rest of tubes for this test.

Test 7

Even that I've tried the Mullard 12AX7 reissue in V2 and PI positions and, even in position V1, that was with other tubes in the rest of spots so, it's time to check back my (usually) preferred new production 12AX7 tube. Would it remain the Winner?.

Configuration was like follows:

V1: Mullard 12AX7 reissue
V2: EH 12AY7
V3: Sovtek 12AX7-WC
V4: Sovtek 12AX7-LPS

WOW!, I am feeling at home again. To me, there are just a couple of new production tubes that can go better than the Mullard re-issue. First one is the Genelec Gold Lion reissue but, it has prohibitive prices, even expensive than NOS tubes. Second one is a good Ei tube but, those can be heaven or hell and, they are very prone to go microphonics in a very short time.

So, the more consistent new production tube, with outstanding sound (very close to NOS tubes) is the Mullard reissue. A limited run and (a bit expensive) of New Sensor factory. It's a very linear tube and goes best the harder you push it (as happens with the Mullard EL84 reissues of same factory).
So, if you can run your amp really crank, be sure to test this tubes. They are awesome under gain but can sound a bit weak and hi-fi if they aren't pushed enough.

Without any kind of doubt, the best defined note-by-note sound of all tested tubes. It's hard to make it to loose the focus, even under high (very high) gain applications. Takes all pedals with ease, remains quiet in V1, has slightly less gain than the JJ or the Tung Sol, better crunch than the EH or the Svetlana and, goes better the most you drive it.

Overall, the cleans had the right amount of basses, not sounding as bonny as the EH or JJ (compared to the Tung Sol). Trebles were in the leage of Tung Sol or EH or JJ. Has some slight bump in mid-highs that is more noticeable in British voiced amps, as this one. Nothing that cannot be corrected with the right EQ in your amp.

Then, Heaven is on the crunch channel. Takes way easier any pedal and gets a massive amount of gain without loosing the definition. The crunch sound is just perfect and allows you to get nice chops and palm muttings (maybe, Svetlana's ones are slightly better). The fuzz seems to bring back a high feedback (as in other tubes) but, way more controllable than in the rest of tested tubes.

To be honest, after my first try, I wasn't confident that this tube will be the best for this amp but, once again, it does the job in spades, as soon as you can crank your amp enough. Fortunately, that 12AY7 in V2 let you crank the amp without going into ear-destroying loudness levels.

Tests I did in other amps, said that a NOS tube, as the RTF ECC83 can refine slightly more this sound (and, that's hard, since the Mullard RI is awesome) but, I don't feel on the need of do that test. I prefer to save this tube for more simpler designed amps, as the Vox Night Train or the Fender Princeton, where the tube swap is way more noticeable than in the Marshall.


As ever, the Sovtek 12AX7-LPS is a true enhancement of the PI position (V4). It's all about of how do the amp responds to your playing. The LPS gives you immediateness and allows you to play speed riffs. My tests with a 12AT7 in this spot didn't liked me. Even that the 12AT7 has higher transconductance levels, it made the rest of tubes to sound weaker and thinner (maybe because it's draining 10 times what a 12AX7 tube can drain). A Chinese tube can work also good here (I've tested in other amps) but, the LPS is just what the doctor recommended me for PI spots. Glad to see that works also good for the Marshall combo. Just wondering how much will it last, since this is the real issue with this tube.

Even that V3 is a non tone-shaping position, to have a specifications-correct tube there helps to have a responsive tone stack and a good working reverb effect.  The Sovtek 12AX7-WC was a good election for this position, even that a Chinese valve can do the job h ere .

I am glad to reviewed my notes and saw the comments of Myles Rose respect of putting that 12AY7 in V2. That changed the vibe of the amp to "vintage" and, helped me to get great sounds at lower loudness levels. The EH 12AY7 is a good new production tube, very close to NOS 12AY7 but, if you want to go for NOS tubes, they can be found at very reasonable price tags.

Respect of the main tone-shaping tube, V1, election can  depend on each particular situation.
If you are able to crank your amp enough, don't doubt it: Mullard 12AX7 reissue hands down.
If you aren't able to crank your amp, probably, best election is the Tung Sol, since it can deliver a musical and full bodied sound at lower loudness levels.
EH and JJ work really good as V1 in this amp. Nothing to blame about but, surprisingly, the JJ works even better than the EH (except for the crunch channel, where the special crunch of the EH is more appreciated).
But, at lower settings, I think the best tube is the Svetlana. Has everything you can have in the JJ but, more refined, more silkier and, in the crunch channel is simply outstanding (slightly better than the Mullard but, with less definition note-by-note).

To me, dices are thrown and, my election is clear:

V1: Mullard 12AX7 reissue
V2: EH 12AY7
V3: Sovtek 12AX7-WC
V4: Sovtek 12AX7-LPS

When having some time, I would like to make some video demoing how the amp sounds with this retubing and, how it takes pedals in each channel. Stay tuned!!!.

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