Ampeg B15 woes.... no sound from guitar

[Jazz P Bass]

O/k.
Then the problem is before the power tubes.
Until you get the 'no signal at the grids' issue resolved, I would remove the output tubes.
I believe you stated that the 'Ext Amp' send worked into another amp.
If so, then that leaves the phase inverter circuit.
Do you have a known good spare 6SL7 tube?
If so try it in the phase inverter socket.
If no spare, use V1 OR V2.
Input 1 uses V1 (tube 1)
Input 2 uses V2.
So whichever tube you take, use the other input.
Now see if you have signal at the grid pins.
Going in the Ext Amp jack would bypass the input circuit.

[Ted]

There's a 1K resistor connected to pin 6 of V3 (The phase inverter). Check that the other end of this resistor is connected to 0V /chassis ground. It should be. If the amp's original 4 core speaker lead has been removed then a connection should exist here.

[lstead]

this is driving me mad!!! tried replacing the inverter tube... no difference 00.00Vs. i also checked the 1K resistor, which is grounded and working correctly.....any thoughts??? sorry to be a squeaky wheel!!!!

[52 Bill]

What are the dc voltage readings on the plates and cathodes of the driver tube?

[lstead]

cathode 2.5v, anode 195v, plates pin 4 2.1mv, pin 1 3.4mv on idle. by driver tube do you mean V1?

[lstead]

got it!!!!!! bad connection on pin 1 on the inverter!!!!! many, many thanks to all concerned; wonderful forum!!!