Who knows about transformer operating temps?

[mort]

The voltages are not making your amp run hot, the plate current & overall current draw is. The colder you bias your amp, the cooler it will run, but the higher the voltages you will see.

It' possible that with EH/JJ 6V6s you can still continue to run the 5AR4/GZ34 if you wanted, if the amp is a '66 then this is probably what it came with. A 5Y3 would reduce B+ voltage & plate current & cool the amp, but really I'd suggest fitting a bias trim pot, adding a trim pot in series with the 22K bias load resistor on the bias board.

With EH power tubes try up to 23mA @ 470vdc max, I wouldn't go much higher on the plate current at any voltage, no matter how low with a 5Y3. JJ will take 30mA at 425vdc up to as much voltage as the amp can deliver at mid 20's on the plate current. If you want to stick to NOS, then you'll have to run them hot (<30mA) to keep plate voltage reasonable, or go with the 5Y3.

A Princeton Reverb has a PT rated for 2A heater current, stock tube compliment is 2.1A...borderline straight off the bat, they are likely to run on the hot side.

Thanks for the post.

It has Sovtek 6v6GT's with the grey smoked glass. I don't know how those compare to the JJ's or EH's, or if it would be of any benefit to get some old stock tubes. The 5AR4 is a modern Fender branded chinese tube, don't know the maker. I do happen to have a USA built, Fender branded 5y3GT. It is marked 81-52 188-5, which I believe would make it GE from late '81. I'll give it a go and take some more temps. Also, how would a 5u4gb effect things compared to the 5ar4 that is in there now? Are the new and old ones different animals in this regard?




For now, I'd kinda rather not make any changes internally if I don't have to.

[MWJB]

I wouldn't fit a 5U4GB because it is a 3A tube, rather than a 2A tube like the 5AR4/GZ34, 5V4, 5Y3. I suspect your 66 amp did not come with a 5U4, so may not have the current capacity for a 5U4G.

The old Sovtek 6V6 do not have a good reputation, but I have no personal experience with them. I thought that they were superceded by the EH & Tung Sol 6V6, which are made by the same company (Reflector) who makes Sovtek? If keeping the heat down is your concern, then either the EH or JJ biased conservatively are your best bet.

Don't worry about making changes internally, IF the amp is running too hot you are better off doing something about it before something burns out & you are forced to change, bigger, more expensive internals that will have a bigger impact on resale value. Buy some bias probes, read the plate current, find some EH 6V6 that run at <23mA, with the GZ34/5AR4 & still sound good.

[mort]

Thanks for the "to the point" advice.