JCM800 Volume

[Ted]

Got a JCM800 2210 here. Definitely not as loud as it should be.
Gives a healthy output with a signal injected at the FX return.

Both the Clean and Boost channels are weak. All tubes test good. On the Boost channel you need the gain at nearly 10 before anything happens, with the volume knob not doing much until about 8 where everything comes in at once.

Schematic here:
http://www.ampwares.com/schematics/m..._100w_2210.pdf

I'm suspecting the CA3046 that switches between channels.

(Incidentally that use of a W005 Bridge rectifier between V1B and V3A ....)

[Jon Snell]

To check the CA3046, (which is totally obsolete) scope the signal both in and out of it. They should be almost the same in amplitude.
Hopefully, it is not faulty, they normally fail totally, not go low level.

[Ted]

It looks like it works by shunting signals to ground - so there are no inputs and outputs as such.

[Jon Snell]

What I meant is to check it mutes when the correct pins are switching levels.
The joys of dyslexia. Sorry.

[drewl]

The volume does go up slowly on these.

Did you check the fx loop Jacks, or apply a signal to the return jack?

Fwiw I have replaced the 3046 with a socket and transistors.

Then I found a few tubes of 3046's at work.