Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Crispy on June 27, 2015, 12:02:56 pm
-
Last time I was here, I had converted my Princeton to run a 6L6, but having trouble getting to the 27W dissipation where a 6L6GC would normally run in a SE Class A amp. Figured out I can't get there without exceeding the current rating just by reducing the "size" of the cathode resistor. Due to Ohm's Law, I need more plate voltage to get there, which would require switching to a SS rectifier. I think instead, I'll just try a lower power 6L6 variant, such as a Tung-Sol reissue 5881, or a short-bottle RCA, and see if I even like the way it sounds better, or not.
-
There is no sin in running a "35 Watt" 6L6GC at 20 Watts. It will be quite happy, and should live forever.
You "missed" in that if the chassis can only put 20 Watts into the tube, there *may* be a cheaper tube which would work. However there isn't. Certainly buying another tube isn't cheaper.
I strongly suspect the new-made "5881" is 6L6GC guts, perhaps in a different bottle, perhaps just a different marking.
What is your plate and screen voltage? What current are you at now? What is your OT impedance??
-
Most I got out of it was 25W, but at 70ma at idle, not healthy. Went back up on the cathode resistor, at about 20W now, forgot the current reading, but a lot closer to 58ma. Sounds good, but I think it would be about perfect with a tube rated at 23W. 5K winding on the OT. 398V plate to ground, about 378 actual.Need to be 400V+ to get to 27W without excess current. Got it all wrote down somewhere, but it's all good. Just not that 90% of max dissipation they say to shoot for in Class A. I get used pulls from amp shops pretty cheap, but it's gonna be tough to beat the Svetlana / Winged "C" I paid 10 bucks for that's in it now.
-
Pin 3-8 357V, 25.8V dropped across 403 ohms=21.6W, or 72% of max, plate current at idle 60.5 ma. Could be biased hotter but sounds pretty darn good. Not crazy about the distortion flavor when it's cranked hard, but I rarely go there anyway, plus, I have pedals. Still want to try a lower power tube. A 23W tube would be right at 90%, then I'd know what that sounds like.