Traynor YBA-1A High Screen Voltage

[rockinrob]

I don't see that you gave us any information about how the tubes are biased in your amp. Voltage is one thing, but it is current that melts tubes.

Is the 28 and 29 ma on the tubes a problem? That is right in line, correct?

[g1]

That's about 65% (at 570V plate). Though it sounds reasonable, the factory spec may be much lower than that, maybe closer to 50%.
I would suggest you try to go as low as you can till you find the tone unacceptable, then back off a little.

[Justin Thomas]

... No way you could put 800Vp on a new JJ el34. No way. So what do you do with tubes that DON'T have any actual spec sheet? I guess you just try $h!t until something works?

There's always the Slobtek 5881WXT... the tone is Bluh, but at least it probably won't die in a Fourth-Of-July show. Might require some creative reworking of bias supply, and your amp probably won't sound the same. But you <COULD> always buy a replacement PT to lower the voltage. Of course, it may require some creative reworking of the bias supply, and your amp probably won't sou-

Oh, wait... damn.

Justin

[Leo_Gnardo]

There's all those possibilities, now including Justin's 5881 Sovtek. FWIW I like to use KT88 in these old Traynors now. Unless you're stuck on the EL34's pentode "tone", the 88's are worthy of your consideration. If you must have skinny glass tubes, maybe KT77. No pentodes these, KT stands for kinkless tetrode, they have beam "forming plates" aka blockers like 6L6 & 6550.

[Pedro Vecino]

In these cases I use a zener connected in series with the screen grid resistor. With 565V I would use a 100V/5W zener connected in line prior to resistor.
If the voltage is greater than 480/500V I use always E34L JJ with a conservative bias setting.

[Chuck H]

KT stands for kinkless tetrode, they have beam "forming plates" aka blockers like 6L6 & 6550.

Which should also mean lower screen current IIRC.

[mozz]

Do you have the fan? There should be one in the 1A.

[Chuck H]

The EH kt90 has some pretty impressive specs. Haven't tried them but it keeps the skinny look and they don't cost a car payment.

[g1]

These are all good points and I don't mean to disagree with any but there are plenty of these things out there running stock that are not eating power tubes.
Often when problems are reported adjustable bias has been installed. This leads me to the conclusion that they are biased much colder stock than they end up after being adjusted. I could be wrong but I think it's a good hypothesis.

[Chuck H]

These are all good points and I don't mean to disagree with any but there are plenty of these things out there running stock that are not eating power tubes.
Often when problems are reported adjustable bias has been installed. This leads me to the conclusion that they are biased much colder stock than they end up after being adjusted. I could be wrong but I think it's a good hypothesis.

Maybe? It's a sorta rare model of that amp. It's not exactly loaded with modern features so new players aren't digging them up. Not enough presence to hear much about them.?. Add to that the higher typical wall voltages nowadays. Add to that the tenderness of newer EL34's and the notable lack of real 6CA7's. So maybe the amp would work biased cold and expressly NOT clipped. Not sure. My own experience with modern el34's say's nope.

I say go with a tougher tube. They will be stressed a little harder even than the tube it was designed with due to modern voltages and the inevitability of clipping the bejeesus out of it. Such as wasn't so common when the amp was designed with tougher than modern tubes that you can no longer get. Just sayin'

KT88
KT90