He's not dealing with a twin triode, per se. The two sections are very different. One section is half of a 12ax7 and the other is half of a 12au7. In other words, a dual-triode tube with a high-mu section and a low-mu section. he has a stereo amp and what he was saying is that one channel was reading different from the other channel. That's why I said his TUBES are not matched (not sections). But your point can hardly be over-emphasized. Our dear friend is obsessing over minor variations in voltage readings which can be entirely attributed to normal variations from tube to tube, even from the same manufacturing run. Now BIG voltage variations, that's where u want to start worrying.welcome to the real world......
twin triodes do not have the same identical characteristics between sections,
that is why they measure differently in yours,
and there is no big reason for them to be so...
also with tubes, just because the scheme says 100v, so it should be 100 in your circuit,
tubes are never like that, as your experience have shown...
changing plate and cathode resistors changes the gain and output swing of that stage,
as you said you did not hear any different....
As you have discovered, experience teaches us a LOT.
I'm not correcting you to hassle you, I don't want our friend to get confused, so I'm trying to be precise.
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When you refer to the “preamp” of the ST-35, I assume that you are referring to the 12DW7 voltage amplifier and cathodyne phase inverter. The ST-35 has no preamp but the integrated SCA-35 is essentially a ST-35 with a “preamp” section added.
I’m not sure why you reduced the B+ voltage to the output tubes to 300 volts. I’ve run JJ EL84s with 390-400 volts supplied to the output transformer for at least 1000 hours without any issue, and I’ve used a few other brands over the years with B+ voltages as high as 430 volts, also without problems. I’m not advocating voltage this high; my AC line voltage ran unusually high at my home at one time.
You may be interested in reading through a thread on another forum in which I (paart) helped another individual work through a similar problem.
diytube.com • View topic - Dynaco ST-35 voltage readings
I’m not sure why you reduced the B+ voltage to the output tubes to 300 volts. I’ve run JJ EL84s with 390-400 volts supplied to the output transformer for at least 1000 hours without any issue, and I’ve used a few other brands over the years with B+ voltages as high as 430 volts, also without problems. I’m not advocating voltage this high; my AC line voltage ran unusually high at my home at one time.
You may be interested in reading through a thread on another forum in which I (paart) helped another individual work through a similar problem.
diytube.com • View topic - Dynaco ST-35 voltage readings
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