Re: Re: Following 2 Power Tube Amp Design

[Andy]

For #2, that could be a source of noise but likely not what you hear. I would not worry too much about that right now, at least not until you have guitar signal coming out.

For #1, the input wiring is a source of confusion because it doesnt make sense on the surface. It sounds like what you have is right. THe 1M resistor is setting the input Impedance and does go to ground. Your guitar input is going through 3 (in your description, Tip is more accurate) through the 68K to pin 2 on the 1st tube stage.

The way the boost switch works is that it switches between just the 1.5K resistor to ground, or the 25u, or the .47u in parallel with the 1.5K to ground. But the 1.5K goes to ground, this is from the tube cathode and is part of the biasing.

You may need to get in there and get some voltages. Be careful!

Its hard to say where to start, Im sure some of the other members will have some thoughts. Personally, I would make sure the voltages are what you expect first. DC first, then AC. You want to make sure to have the right DC power to the tubes, and AC filament power. Make sure the rectifier is supplying the right voltages. Check the power coming off the Power transformer, all that.

Another thing to check is grounding. Its possible that the guitar signal is getting grounded somewhere and not making it though the amp.