Check this out, I knew the reverb never worked so I left the gain channel on the back burner for now. I saw that there was no plate voltage on the b side of the reverb tube. I had a plate resistor that was open so I replaced it and now the reverb and boost channel work 🙂
Your voltages are correct. The reason the cathode voltage of V2b is high is because this stage is a cathode follower. With the cathode at 92 vdc, and the grid at 90 vdc, it is no different from the grid being at 0 vdc, and the cathode at 2 vdc, which would likely seem quite normal to you.
Since the gain of the normal channel is good, and the problem only affects the gain channel, -- and because you basically haven't done anything to the gain channel preamp, I would concentrate on the channel switching circuitry. I would try disconnecting the cap from the switching transistor that connects to the wiper of the level control feeding V2a. This will prevent the switching circuit from shorting the signal at that point. There also appears to be a grounding circuit connected to this same wiper that goes back to the input jack to short the channel out at that point when no input is connected. Make sure this is not grounding out the signal as well.
The voltages on the tubes appear normal, so this problem should be relatively easy to find -- a lose connection or short is likely.
Dave
Since the gain of the normal channel is good, and the problem only affects the gain channel, -- and because you basically haven't done anything to the gain channel preamp, I would concentrate on the channel switching circuitry. I would try disconnecting the cap from the switching transistor that connects to the wiper of the level control feeding V2a. This will prevent the switching circuit from shorting the signal at that point. There also appears to be a grounding circuit connected to this same wiper that goes back to the input jack to short the channel out at that point when no input is connected. Make sure this is not grounding out the signal as well.
The voltages on the tubes appear normal, so this problem should be relatively easy to find -- a lose connection or short is likely.
Dave
I assume you are talking about V4b? If the plate load resistor was open to that tube, the reverb definitely would not have worked. However, repairing that would have nothing to do with the gain channel functioning properly. I'm glad its operating properly for you now, but I would check that some intermittent lose connection or short is not the ultimate problem with the gain channel.
Glad you're starting to get to the bottom of this thing!
Dave
Glad you're starting to get to the bottom of this thing!
Dave
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