Valvecaster Question.

[pjones78]

So, like everyone else, I dove into a Valvecaster build. Everything is "stock" to the original Matsumin schematic. What I am running into is a volume control question.
I hook up my A100 pot for volume control, and my over all volume decreases. The volume control works, but when I take it out of the circuit, it becomes louder. What can be done to retain the volume output of the circuit?

[GibsonGM]

Ok, all things being ok, that means the 100K hanging on the output in parallel is loading the circuit down, even when vol. is maxxed. You could TRY a higher-valued pot with no risk other than a possible slight change in tone as the Valvy plays with other pedals/amps....  500k, 1Meg...

2) you could try removing the tone control, that MAY gain you some volume back...

3) run it at higher than 9V.   12, 14, 18V....this would be the route I'd take. 

[PRR]

> A100 pot

100?? or 100K?

The plate impedance of 12AU7 at that point should be near 10K. A 100K load should be a just-audible drop, no big deal.

[Cozybuilder]

Also check the tone cap (C4 10nF), make sure its not shorted.

[pjones78]

100K. I'll check the tone cap when I get home this evening. If anything else,  I'll drop the volume. Its fairly loud by itself.

[amptramp]

Checking the printed values of the Rp in the plate characteristics given in the GE Tube Manual, I get about 14K, not far off the value Paul got.  Think of the tube as a voltage source in series with Rp and you are now hanging R3, VR2 and VR3 off the end in parallel.  You have a load of 50K dropping to 33K with the volume control added.  The gain is 0.7 µ with the volume control and 0.78 µ with no volume control with the tone control at max treble.  This should not be all that obtrusive.  Are you sure you had the tone control at the same setting with and without the volume control?  It will have a large effect on gain.

At its maximum resistance, the treble control rolls off at 159 Hz.  If the tone control is set less than 100K, typical guitar tones will see a lower resistance and the gain will drop as it is in parallel with the load.