tube output
- Thread starter AL1
- Start date
At a little over 9 watts plate dissipation per 6V6, you have them biased at a good point for getting good tone and long tube life. For a bit fuller and warmer tone, you can safely go a little higher and bias them at perhaps 24 or 25 ma per 6V6 at idle.
But since this is a Princeton Reverb, which has a rather small power transformer with limited current capabillity on the seconday (B+) , you're simply not going to get more than around 12 watts of output power at clipping. Paul Cochrane has described a couple of mods to the the phase inverter circuit that might bump this number up by a couple of watts, but that's going to be it as far as what a Princeton can put out.
No matter what the specs of the output tubes are, an amp's maximum power output capability is ultimately determined by its power supply.
Blue Strat
Member
True, but the power limit of the output tubes is the final limiting variable. I'll bet this was what the original post was asking.
This isn't as big of an issue with the earlier (original blackface) Princeton Reverbs that have the GZ34 rectifier tube, since the GZ34 takes significantly longer to warm up and supply current to the rest of the amp, compared with the 5U4GB.
If the multii-section filter cap in your amp has been replaced, then it's probably rated at 475 volts per filter, so 485 volts is probably OK for a few seconds. If your amp still has the original filter can, you might be asking for trouble, since it may be pretty dried out by now. The tubes, if good quality, shouldn't have any trouble dissipating a few extra watts beyond their max. plate dissipation rating for several seconds.
I don't know whether or not any significant cathode stripping would occur during warmup. (This is where a tube's useful life is shortened because the cathode coating gets "stripped" while it is still cold when high voltage is applied to the plate).
A cool and easy mod for these amps (I did this to my '69 Princeton Reverb) is to get rid of the polarity switch and replace it with a standby switch (so you don't need to drill a new hole in the chassis). The standby switch should be wired to go between the output of the rectifier tube and the first (main B+ supply to OT primary center tap) filter cap.
Yes, but in this case, the first filter (one of four in the multi-section can) is rated for 450 or 475 volts max. working voltage. While in standby mode, the voltage on it could go well beyond the max. value. That's why I recommended the "tweed" style setup instead of the usual blackface wiring.