Traynor YGL-3/Mark III - 6L6 vs 6CA7

[Janglin_Jack]

I did some service on 4 of my buddy's amps and as a thank you, he handed over to me his old Traynor YGL-3. It has standard a quad of 6CA7/EL34 tubes. I noticed it had 6L6 in it. I do know that years ago he took it to a reputable tech and had the amp serviced. There seems to be a proper 3 prong power cord and from what I can see, two 100K resistors were changed (to metal oxyide). Everything else appears to be totally stock. I think one of the main differences between the power tube socket wiring is the suppressor grid on the El34 is Pin 1 and I think Pin 1 is not used on 6L6 as that is wired to the cathode internally in the tube. So what happens if you just plug in 6L6 tubes into a stock YGL and not rewire it? The tube bases look like the have gotten pretty hot as they are discolored a bit. I haven't flipped it on as I am going to review the entire circuit first.

Can you just drop in new 6L6 and rebias?? FYI - I want to put in the proper EL34.

Mike

[Janglin_Jack]

Well, the schematics I have are hard for my old eyes to read. There is one conveniently pasted into the top panel of the amp. I printed one that is just fuzzy enough that it is hard to make out some of the values. It appears to me that there is a feed off the PT providing a -325v (negative voltage) to pins 1 of the power tubes - that node is also attached to the tremolo circuit. So if an EL34 tube is used, that voltage is supplied to the suppressor grid pin 1 of the power tubes as intended. If a 6L6 tube is used pin 1 is not used, so that voltage is not used. I believe I read that the suppressor grid is somehow wired internally in the 6L6 tube so that voltage is not needed from Pin 1. Does that mean that no modification is needed to run 6L6 in an EL34 amp, (more specifically in this YGL-3) except a rebias? .

The schematic inside the amp shows 22ohm resistors tied to pin 4 (screens?) and 1.5K on pin 5 (control grid?).

It still appears that the amp is stock and they just plugged in 6L6 tubes and probably rebiased. Until I fully understand what should be changed from stock to PROPERLY run 6L6, I am still not sure of any other changes that MIGHT be in the amp. I still need to review every connection.

If anyone knows all the changes that might be needed to run 6L6 in this Traynor it would go a long way in helping me narrow down where to look for changes.

Thanks again!!
Mike