Right back to basics/ pg1 Qs.

[Chuck H]

I had an idea many years ago when everyone was having trouble with their DR's and high plate voltage eating 6V6's. It's been two decades since then and now there are 6V6's that can take it and, of course, the trend toward upgrading to MM transformers and such. But back in the day I thought "Why not just cathode bias the amp?" This effectively floats the tube at the bias voltage and removes that amount from the plate. That is, it's the plate to cathode voltage that is the "working voltage" of the amp. So You're basically taking the bias voltage from the B+ rather than providing it separately. If you don't like cathode bias then strap a zener across the cathode circuit and Bob's your uncle, fixed bias. With 35V or more effectively removed from the plate circuit.

[g1]

The other thing is to check the heater voltage to see if it reads 6.3v loaded.

Can you check this Chief?
If it's within reason, then it's ok to talk about reducing only plate voltage. If it's something way high, the reduction should be done on the primary side of the PT with a bucking transformer. Or the unit should be returned as defective. While you're at it, measure the voltage at the wall outlet.

[Chuck H]

+1 to what Mick and g1 said.

[Dave H]

There's always a caveat to this idea tho surely Dave-?

The B+ supply will be less 'stiff' with the resistors but that could be a good thing if it's too high because the Hammond PT has better regulation but as others have said check the loaded heater voltage first.

Cathode bias will reduce plate voltage but you'd probably want to increase the bias current in cathode bias and the plate voltage is too high for that. Fixing it with a zener would reduce plate voltage by 35V but as with cathode bias the bias adjustment is lost. Below is a circuit which reduces plate voltage by 40V and retains bias adjustment. It is 'fixed' bias as required for a DR but would also work for cathode bias (zener replaced by a resistor).

As you can see there are many ways to reduce plate voltage without spending £100 on a new PT.

[Attila]

Hi Guys, forgive me wading in on an oldish thread,

Be careful when using a wire wound "anything" (the Rheostat in Chucks circuit) in an audio circuit as you'll end up with certain frequencies missing due to cancellation effects, One could place a highpass cap over the circuit which kinda works but only to a degree.

IMHO the Webber mass circuit is a much more scientific in design .... just saying