Amps: Orange DIVO VT-1000 Tube Tester - Testing my stock of tubes

Introduction

Since the very first instant I've seen the presentation of this Tube Tester, I wanted it. I had three months to save money for it and, it came today.

Tube Stores doesn't give you information enough about how they match their tubes and, even selected tubes say nothing about their own matching values. To check for balanced triodes in 12AX7 is a notable overcost for the tube.

Why tubes "selected" by the Tube Store behave so different, from tube to tube (same brand / model) tested in the same position of same amp?.
What is the Store selling me as untested tubes?.

Today, I had the opportunity to check my whole stock of tubes and, results confirmed some suspects I had, while trying tubes in different amps and, I had some surprise also related to the matching system of TAD.


Orange DIVO VT-1000

The unit comes in an Orange cardboard box.
Inside two black cardboard boxes have, one the unit and user manual, the other has the AC/DC adaptor.
As a gift, they are sending you a Shirt with Orange's Logo and, a plug adaptor UK/Europe.

Here some pictures (click for full size):

The unit is very easy to handle. You only need to insert the tube in the right slot. From left to right hand: Octal Power tubes, EL84 and 12AX7 family.

Once you insert the tube, you click the OK button and, with the help of the two side buttons, you select the tube type you want to test. Then, after pressing the OK button once more, the test begins.

Results show if the tube is Good, Worn (a new one it's recommended) or Fail (you can throw it).

In case that the test fails, you should stop the test, pressing once more the OK button, remove the tube and throw it to the trashcan.

In the case that the tube is in a working condition (good or worn), a light will indicate the Matching number determined for that tube. If the tube has double-triode, as in the case of the 12AX7 family, two lights will be shown, one by triode (except in the case that both triodes are balanced, where you will see a single light).

After every test run, press the OK button to switch off the tube. Wait a while (to cool it) and remove it. Insert a new tube, press OK and, if you are still testing same tube type, press OK again to start tests.

Tests take about 2 mins for a 12AX7 tube and, about 3 mins for power tubes.

During the test, I've seen a JJ ECC83S tube lighting as any lamp, with a bright light. This tube failed.
I've also detected a couple of bad tubes in my stock. Rest are all in Good condition, what are good news.


Tables of results

I've labeled each tube with the Matching numbers determined by the tester and, filled in some Excel sheet with results, to analyze later.

12AX7 family

Here a picture of the table of results for this family of tubes.

In this table, each tube has two Matching numbers corresponding to both triodes (A and B).
Light red shadowed cells mean tubes that came stock in some amp.
Light grey shadowed cells mean tubes for which I've requested triode-balancing test (overcost).

Not sure about which criteria follows DIVO to determine the Matching value but, in my understanding, it's associating such a value depending on the percentage of compliant with gain standard.
So, a value of 10 should mean that the gain is 100, while a value of 8 should mean a gain of 80 (under specifications). This is what it seems to me, if I compare this results with "my sense of gain" I had while trying those tubes.

One of the Tube I hated more are TAD's 7025 tubes. What I've expected from a tube labeled as 7025 is the highest level of compliance of 12AX7 specifications. First tube has very unbalanced triodes (8 and 12), while the second tube is balanced and closer to specifications (9).

What's the meaning of Highgrade here?. Just balanced triodes. Each 7025 Highgrade tube has a different Matching value (8, 9 and 10).

TAD 7025-S tube is, instead, one of the best sounding tubes around. Very rich, a tad dark and full bodied, with very linear behavior. But, they seem to fall a bit under specifications. One tube has balanced triodes with a Matching Value (from now, MV) of 7, while the second has unbalanced triodes with MV of 7 and 9.

The Highgrade version of this tube just seems to have balanced triodes and a MV of 8. Not a great difference.

The TAD 7025-WA is a nice sounding tube, also. Surprisingly good. As a WA type, its gain should be inferior to the nominal gain of a 12AX7. It shows unbalanced triodes, with MV of 6 and 8.

The TAD ECC803S seems a perfect tube. Balanced triodes with a MV of 10. This tube is a "selected" JJ ECC803S tube.

Now, it comes an interesting comparison. The TAD 12AX7-Cz tube is a "selected" JJ ECC83S. We can see same values in both tubes, unbalanced triodes with MV of 8 and 9.
I bought also three JJ ECC83S tubes (unselected). From those three, the first one never worked, because a triode was failing. The other two failed during today's test.
My Marshall amp came with Marshall labeled versions of JJ ECC83S and, they show very similar values. First tube has MV of 8 (balanced), second is 8 / 10 and, third is 8 / 9 (same as TAD ones).

I am suspecting that, when a Tube Store has two version of the same tube and, one is selected while the other is bulk, they are selling you the crap as bulk, while relabeling the poor percentage of tubes that cover the minimum values to be "selected".

In other hand, if the Tube Store doesn't have a selected and a bulk option for same brand/model, it could mean that that particular tube has a consistent production. This is the case of the EH tubes, that seem to be very consistent in values. Same can be said of the Tung Sol and Mullard reissues.

Myles Rose identified the Sovtek 12AX7-WC as a tube very close to specifications but, my tests in my amps, made me feel the opposite. After testing them, it's clear that they are more inconsistent than the three commented above and, their values are under specifications.

Probably, the most inconsistent tube is the TAD 12AX7A-C, a Chinese tube built by Sino and "selected" by TAD.  The good thing is that has a good gain and, in some cases, over specifications. The bad thing is that triodes seem to be very unbalanced. The values of the bulk Sino (unselected) 12AX7A are very similar so... what's TAD doing for those tubes?.

I payed an extra cost to TAD to have Sovtek 12AX7-LPS tubes with balanced triodes (since they are my first election for PI positions) but, you can see that just one of the two have the same MV value for each triode. The third one corresponds to a tube for which I didn't requested balance test, and clearly has lower MV.

Surprise is that NOS RFT tubes doesn't show a great consistency neither.

I have to warn you that DIVO doesn't seem to be able to check a 12AY7 tube, neither a 5751 so, some of my tubes are still an incognit.


EL84 family

This is were things go really weird.
Since I am buying all power tubes as matched pairs, quartets or octets, I cannot understand a different MV for each tube of a matched set.
The other thing that drives me crazy is the Magic Pair used by TAD to match their tubes.
They are being matched according to what?.

The last column corresponds to the Magic Pair given by TAD to the set highlighted in light grey.
You can see that same Magic Pairs result in very different MV.

By example, the EH EL84 quartet was requested with Magic Pair 6. They have values between 9 and 11.
But, if we compare them to the TAD EL84-STR, with same magic pair, we have MV of 8.
Even more crazy, the EL84M are rated to a maximum of 4 as Magic Pair but, they have a MV of 10, more or less like the EH (rated as 6).

The Gold Lion is a very weak tube. I bought two pairs. The first pair dead during the first three working hours. Of the second pair, one tube was detected with failure, during tests. They are expensive as hell and, indeed, they have the best EL84 of all tubes but, they are so weak that I gave up buying them anymore. Surprisingly, the one still alive shows the highest MV of all tubes.

The consistency level of EL84 tubes seems to be higher than in the case of 12AX7, anyway.
Just the TAD EL84-STR and the JJ are slightly under specs.


6V6

In ligt grey, pairs or quartets. I have no info about the Magic Pair corresponding to the Tung Sol quartet. Just one tube as an slightly different MV (10). Tube number 5 corresponds to a bulk tube.

Once more the weird matching system of TAD, giving a value of 0 to a tube with a MV of 8. The other JJ tube has same value (I've forgot to update the sheet).

Tung Sol seem to be the closer to specs and, maybe that's why they are the common election for 6V6 tubes. In fact, Tung Sol seems very consistent in their tubes.


EL34

Since the only amp needing EL34s is my Marshall and, Winged C is the natural election, I was able to compare just the stock tubes with a quartet of Winged C that I have ready.

Very similar values between the stock tubes and my quartet (the other two tubes are in the amp, currently).


Conclusions

Indeed, the Orange DIVO VT-1000 is an expensive device but, it helped me to classify my tubes and, this will help me to better choose the right tube for each application.

If I wanted to raise the gain, to make the amp to sound in the sweet spot at lower volumes, I will choose a tube or set of tubes with high MV.

If I wanted to lower the gain, giving more headroom at high volumes, I will choose a tube or set of tubes with lower MV.

If I want a tube for PI position, I will choose one with balanced triodes. I can save money when asking for a new tube, I will check its triodes myself.

When having doubts, I can get any tube from inside any amp and check if the tube is failing or is worn. This is a typical question: "How long last a tube?" and, it has a single answer: "there is no rule". This device helps to determine the health of any suspicious tube.

This device is also a nice weapon against your Tube dealer. If you requested balanced triodes or matched tubes and, they aren't delivering to you as requested, you have some basis to claim.

Today, I've thrown 3 failing tubes and checked that all the rest are in good condition and, ready for any use. That's awesome.