Marshall style phase inverter clipping

[stiltamp]

Hi,

I asked this questions on different places but I had not got a satisfy answer until now.
What is the amount of the direct PI input signal level that the PI-outputs starts to clip respectively to overdrive.
Marshall PI-Type 100kOhm and 82kOhm plate resistors and 470Ohm+10kOhm+4,7kOhm cathode resistors.

Who knows the answer it would be great.

Manfred

[Jana]

I don't think you can get an exact answer to that question. It is also going to depend on the voltage to the PI section, the feedback network, where the presense control is set at, the frequency of the signal, the tube in the PI--??--anything else I forgot?

If memory serves me right, which it rarely does, it is about a volt or so.

[Cliff Schecht]

I don't think you can get an exact answer to that question. It is also going to depend on the voltage to the PI section, the feedback network, where the presense control is set at, the frequency of the signal, the tube in the PI--??--anything else I forgot?

If memory serves me right, which it rarely does, it is about a volt or so.

Yeah, you forgot the operating temperature of the amp, the composition of the internals of the tubes, the composition of the resistors/capacitors in the circuit, the tolerances of the components used, how well the tubes are connecting to the sockets, the wall voltage, the type of wire used in the amp, etc... I think you get the point

[Structo]

If this is about a specific Marshall amp, you may get better results over at the Metro Amp forum.
Those guys live and breathe Marshall's and I'm sure one of them can help you answer that question.

Go here:

http://forum.metroamp.com/

[jjman]

The outputs from the PI will clip (actually "clamp") when their swing brings the grids of the output tubes to zero net volts. So if the output bias voltage is (hypothetically) -30vdc, the PI plates will look like they are clipping when they put out 60vac p-p (30vac peak.) So the bias of the outputs affects the point at which the PI plates show clipping/clamping on their wave tops.

If you put in a post PIMV and turn it down, the output bias no longer matters and the PI plates can go higher w/o clipping from the clamping. Turning the channel volume higher will then eventually lead to true PI clipping. This occurs when the grid voltage of the PI section equals the cathode voltage of the PI. I don't know that figure.

This all assumes that the stages before the PI don't clip first (preamp clipping.)

[stiltamp]

Thanks!

The gain of the PI is about 20 to 30.
Then the input signal must be 1 to 1,5V vac-peak for clipping the output.
I'm right?

Manfred