Blues Jr. / 12AX7A vs. 12AX7 replacements?

Should be fine

 

There's no difference. Anything after the main designator is just companies trying to be fancy. *Some* meant something back in the day, but not now.

 

Dim means nothing. Only sound is important. Get some replacements to swap as a test. Any of the following will work fine:
- 12AX7 = a 12AX7
- 12AX7A = a 12AX7 designed for series or parallel heater wiring. Fine for your amp.
- 7025 = a 12AX7 designed for lower self-noise. Fine for your amp.

I'm in favor of NOS or used OS tubes. 12AX7 can be found at rational prices if you shop carefully. Any US, UK, EU, or Japanese tubes will sound fine and you don't need to buy some holy grail tubes for good tone. I've had good dealings with:

audiotubes.com
kcanostubes.com

 

Have you tried subbing out the EL-84 power tubes with spares, in your trouble shooting?

Just trying to eliminate variables.

( I've owned my BJ since 2000, and have had squeal/noise issues with a preamp tube a few times, and a 'flat' or lack of life sound with the power tubes, but never a loss of volume)

 

Just to add to what has already been said, I personally do not think there is a lot to be gained by running expensive vintage or NOS tubes in the blues junior. I really think you are best off by running new glass from a big brand like JJ's Grove tubes or the like. That is unless you believe there is something to be gained in terms of lifespan/durability with NOS tubes.

In my own experience, my BJR is probably the least responsive amp I own (in terms of tonal change) to tube swaps. I have tried a lot of different tubes in mine, both new and old and have only heard nominal changes in the sound of the amp as a result of changing out tubes.

 

I think it was designed the way and I think the only 12AX7 to be concerned with in terms of gain shaping, is the one to the far right. The other two just have to be functional.

 

Regarding that first 12AX7: In my Traynor YCV20WR, I find the gain to be too gritty, square. So I swaped it for a 12AU7 and the gain became much creamier.

 

-S: Slovakia (JJ)
-R: Russia
-C: China
Al

 

There are the "W" variants and also the LPS. These were around with various manufacturers years
before the Sovtec ones at the link. https://valvetubeguitaramps.com/sovtek-wa-wb-wc-12ax7-differences/

 

V1 TungSol RI 5751
V2 TungSol RI 12AX7
V3 Sovtek 12AX7LPS
These are the preamp tubes I retube Jr’s with.
Power tubes I like the TungSol or Sovtek EL84.

 

LOL @ that graph. Sucker born every minute.

It's a blues jr. It doesn't matter what the label is on any 12ax7 you put in there.

 

Isn't the EH-12AX7 a Russian tube?. Also the Sovtek 12AX7WB previously mentioned is for sure a Russian tube. I know New Sensor distributes some Chinese tubes, but I'm not sure if they sell them under the EH label.
Al

 

The LPS is LP- long plate and S-spiral heater filament and therefore a little quieter. It's a longer plate tube with fairly high gain. I think it's personally the best modern V1 tube in Fender BF/SF clean amps, with very smooth and pleasant character.

 

I've tried a lot of different 12AX7s in my Jolida EL84 25w/channel stereo integrated amp, and the EH, long plate Marshall branded Svetlana/Winged C (no longer made), and long plate EI (no longer made) were all good, but the LPS is my favorite, other than the extremely rare and expensive Raytheon with the long black plate.
The new Tung Sol 12AX7 is also very highly praised by all. The EH that I have, that MB uses, is made in the Sovtek (Reflektor) factory, not in China. I generally prefer long plate ones, and I haven't tried the JJ one, their ECC803S, but their regular ECC83/12AX7 (with the frame grid) is a little too dark for my taste. I haven't tried the new Sovtek made long plate Mullard yet either.