Bogen CH 18

[Phyberoptic]

Picked up an old (1940s) Bogen CH 18 tube PA amp from a Craigslisting that is whole except for the power cord which was cut off. Need a schematic and my google searches have turned up empty.

-=Phyber

[DrGonz78]

I am pretty sure this is the correct schematic.

[Phyberoptic]

I am pretty sure this is the correct schematic.

Well the valves are correct, but the one I have is AC only and doesn't have the power plugs referenced or any phono motor control. The transformers called out are different model numbers also. Thanks, as this is the closest, I'll use it as a reference and mod it to match mine which appears stock and untouched. However the large power canned caps used for voltage doubling seemed to have leaked their guts into the lower chassis making some identification of components near impossible.

[Enzo]

I don't see any can cap leakage in your photo. However I do see a number of waxed caps where the wax has run. The wax is over the printing which can obscure it. Waxed caps always need to be replaced anyway. And the simple thing to do is hit them with a heat gun and melt the wax right off, then the printing is clear as a bell.

If the audio circuits are the same, it doesn;t much mater if your amp lacks the DC power suply circuit.

[Phyberoptic]

I don't see any can cap leakage in your photo. However I do see a number of waxed caps where the wax has run. The wax is over the printing which can obscure it. Waxed caps always need to be replaced anyway. And the simple thing to do is hit them with a heat gun and melt the wax right off, then the printing is clear as a bell.

If the audio circuits are the same, it doesn;t much mater if your amp lacks the DC power suply circuit.

Maybe it's more clear in this picture:


that black goo is just below the metal can shown here:


And there are a couple of caps way that are not where the schematic calls out. So it's close but not enough to rely on the tone stack shown as the values and/or placement is changed on my version. Either way there is a few hours of work in repairing/restuffing the caps that are there and I will update the drawing as I do that.

-=Phyber