"Swirly" Distortion Decay Sound Fix !

[Helmholtz]

An underrated OT is likely to cause ugly saturation distortion, limit bass transfer and reduce available output power. When saturation occurs OT primary current strongly increases which may shorten tube and transformer life. In fact during saturation the OT primary impedance drops by a factor 10 or more leaving only the DCR.
As long as there is no saturation, the tubes don't care if the OT is underrated. This means that they will produce the same primary power with any OT having the same primary impedance. But an undersized OT can have power losses of more than 5W. So available output will be reduced by the same amount. The power loss in the OT heats up its thin primary wire and may cause shorted turns.

Without knowing your circuit and full power plate and screen voltages, it is not possible to predict the power your tubes are producing.
But I would at least use a 35W rated OT.

[g1]

Without getting too controversial here (with even higher numbers), if supply is adequate you can even get 60W from a pair of 6L6GC.

Pulling a pair of tubes from a 100W amp (and adjusting load impedance as required) is always instructive for what an overspec'd PT and OT can do.

[HaroldBrooks]

When you say "Classic industries 20W" do you mean ClassicTone 20W Deluxe Reverb transformer? Because if you do then a pair of 6L6's with high-sh voltage from an ample power transformer will be enough to actually jeopardize it without limiting safeguards built in. In which case you're looking at something like 25W to 30W. I've used Hammond 16XX and Stancor transformers rated at half an amps intended watts before without any problems or limitations. But those are full range transformers and guitar amps aren't full range. In fact a tech at Hammond once told me that choosing from their standard transformers it's better to go with a half rated model for predictable tonal results in guitar amp builds. But the amp clone transformers made by Hammond, ClassicTone, etc. are rated for guitar amps. So if you have a ClassicTone 20W OT then it's good for a 20W amp and not much more. Not that using an underrated OT hasn't been done. Hell, it's been done by major brands. But the results aren't usually very satisfying from a power or fidelity angle. So if you want something different than a smallish, squishy amp I think you're going to need bigger iron.

Yes, it's a ClassicTone ! It doesn't overheat or anything, and I have 625v TDK resistors connected between both HT leads and the CT to guard against overvoltages, but I am toying with the idea of adding a better and bigger transformer to this great old RCA amp.

I think the current ClassicTone 20w version I am using is indeed clipping off a bit of the Bass when the amp is driven hard, but I've had enough of that type of compression, and I want this amp to be different, and if that means more "Hi-Fi" like, then so be it.

Bigger Iron it is ! I will order a transformer more appropriate for a Fender Bandmaster I believe, and hope that works out better.

Another question, is 4.2k ohms on the primary side appropriate for a push pull 6L6 amp ? I never got it straight on how that works. The plate voltages are right around 450vdc, and the screens are 335vdc, and I understand about reflected impedance, and the fact that the tube's plate to plate resistance for the pair is also dependent on the plate voltages. Just want to make sure a 4.2k OT will optimize output to a degree.

Once again, thanks !

[Helmholtz]

Pulling a pair of tubes from a 100W amp (and adjusting load impedance as required) is always instructive for what an overspec'd PT and OT can do.

Good point!

(My 1967 Marshall JMP100 Tremolo puts out exactly 60 clean Watts with 2 Svetlana EL34s and a plate voltage of 474V. Plate voltage drops to 448V at full power.)

The GE 6L6-GC datasheet specifies 55W @ Vp=450V for a pair.

[Helmholtz]

Another question, is 4.2k ohms on the primary side appropriate for a push pull 6L6 amp ? I never got it straight on how that works. The plate voltages are right around 450vdc, and the screens are 335vdc, and I understand about reflected impedance, and the fact that the tube's plate to plate resistance for the pair is also dependent on the plate voltages. Just want to make sure a 4.2k OT will optimize output to a degree.

THe 6L6-GC datasheet specifies 5.6k for Vp=450/Vs=400V. Fender typically used 4.2k but with Vs= 420V or higher. Optimum Rpp depends on Vp and Vs. Lower Vs requires higher Rpp.

[HaroldBrooks]

Started the Schematic ! Keep getting interrupted with life matters, but about 1/3 done (maybe). I can see that this will help in the future, even though at this point I am slow, and failed my visual arts courses...

This is an exciting amp for me, because I had to alter it to get it to work, and it works great so far, so I've been both lucky, and lucky to have you guys to lean on !

Please stay tuned for the finished version, and thanks for your patience and all the help.