Different wiring OD-stage Snubber capacitors

[stiltamp]

Hi,

In the equivalent AC-circut of the common cathode stage the plate resistor is in parallel to the internal tube resistance. The cathode resistor is disregarded for this view, because it's bypassed by the cathode capacitor for the frequency range where the snubber capacitors takes an effect.
Thus, following wirings of the snubbers must have the same effect theoretical.
- in parallel to the tube as usual in the OD-stages
- form the plate to ground
- in parallel to the plate resistor.

Did any person make trials with the different wirings of the snubbers?

[heisthl]

I've forgot to put them on the socket before and just added them across the plate resistors and not noticed any difference. It's just cleaner to get them down on the socket.

[marcos]

I tried all the wiring options, and there is an audible difference.I felt that wiring to the tube socket gave the most brilliant sound, wiring plate to ground very similar, but a shade darker, wiring across plate resistor a bit darker again.Not a huge difference,though

[Bob-I]

I've forgot to put them on the socket before and just added them across the plate resistors and not noticed any difference. It's just cleaner to get them down on the socket.

Funny, I've considered putting the snubbers across Rp because it would be cleaner. The socket gets pretty crowded where across Rp on the board would be very clean. JMO

[glasman]

Caps on the plate resistors is pretty common. Even my SWR 500 bass amp uses them. The supply rails are a much better AC ground.

I have built a few amps with caps on the plates of the OD stages. It does take a bit larger cap to achieve the same results.

Gary

[stiltamp]

Thanks to all, for the interesting replies.

Manfred

[Structo]

I guess I am wondering about the properties of what they are doing.

But if they are across the plate resistors that is not the same electrically as from plate to cathode as the ODS is designed, right?
Because of the cathode resistor and bypass cap in series with the snubbers.
But also the snubbers are in parallel with the whole tube really.

I never did experiment with them since I was studiously trying to build my amp exactly as the layout showed.

Interesting to try different things though and that is how great things happen.

[stiltamp]

Hi Tom,

the AC-equivalent circuit has another arrangement than the DC-circuit.
The power supply acts as short circuit, thus the plate resistor is grounded at the powersupply side. The cathode is almost grounded by the low resistance of the cathode capacitor for as little as 2000 Hertz.
The AC-resistance is about 15 Ohms, the snubber has about 300 Kiloohms at that frequency. About this point the snubber effect starts.
The AC-equivalent circuit the plate resistor, the tube internal resitance and the snubber are in parallel for this frequency now.
The reason for my question was the intension to switch snubbers with different values to the ground to get different sounds.

Manfred