I've recently experimented with my studio vintage by changing out the EL34's for some KT66's I had on hand, and swapped the stock 12ax7 in V1 for a tung sol 12ax7 just to see what happened. The change in tone was magnificent to say the least, and being cathode biased I was under the impression this would come without consequence.
2 days later, the amp spat and crackled when I turned it on, then proceeded to work but with very little volume. I thought it must have been the KT66's so quickly swapped them back with no improvement. Then I troubleshot the pre-amp tubes one by one to discover that it was one of the two tubes I'd left in. Not sure which one but replacing both completely sorted my problem. I've attached a photo of the two in question, one of which looks like it is definitely the culprit.
My questions to you experts are:
1) Could changing to KT66 tubes in such an amp have caused this problem in the pre-amp section, or is it likely coincidental that this happened when I changed them?
2) Is there any way to determine the cause of the damage by the visual deformation of the tube in question?
3) What would you advise I do now? I really, really preferred the tone with the KT66 valves but don't want this to be a regular thing.
Many thanks in advance!
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Comments
No, not usually. Those two look normal given the awful quality of modern valves! You can normally only tell if they've failed when the tops go white.
Replace whichever of the preamp valves is faulty - the chances are it's the middle one since that is a cathode-follower position, which can cause failures with Russian-made and sometimes JJ valves.
The valve on the left in the pic is Chinese and the one on the right is a JJ, so if it's not the Chinese one that has died, put that in the middle position. Tung-Sols are Russian so don't use one of those - they're fine in the first and third positions.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I have a bunch of new JJ's so will move the Chinese 12ax7 to V2, keep the tung sol in V1 and a JJ in V3. I didn't know their interactions would be so nuanced! Cheers again for the wisdom. Will let you know how it goes
All accounts I've read on other forums seem to show unanimously positive outcomes from changing the power tubes..
I'm interested in your findings!
I also have a 89' 1962 bluesbreaker RI which has a pair of really well broken in greenbacks. Was thinking of trying them in the 2061cx to see how it sounded, whilst trying some celestion alnico golds in the 1962.
Fun times ahead!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Rob
I quite fancy getting a 2x12 with Creambacks.
Do you think the volume difference will drown out or dilute the sound of the greenback too much? In that case it may be a bad idea...
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The idea of running a greenback and a g12h30, or maybe both greenbacks, in the 2061cx with the SV20h is something I'll definitely be trying out!