Bogen chb35a

[skid20]

I was looking at the schematic for my bogen chb35a and was wondering if anyone could shed some light on why there is 240/260v going to the cathodes on V2 (12ax7)?

Would anyone have an idea what this voltage is being used for in this amp?

I would like to do some modification after I get it back up and running.. just finished changing the electrolytics and have a hammond 1620 on the way to replace the burt OT..

It just that this is different from anything I have seen (yet) and I would like to understand it a little better if possible lol

[rsumperl]

Greetings,
The 220K and 470 ohm resistor form a voltage divider. The voltage at the cathode will be +.55 volts. They use it for biasing the tube.

Ray

[skid20]

Originally Posted by rsumperl

Greetings,
The 220K and 470 ohm resistor form a voltage divider. The voltage at the cathode will be +.55 volts. They use it for biasing the tube.

Ray

Thanks Ray, that makes more sense to me now

[skid20]

Another question I have been struggling with is would it be safe to feed the output of V1a into the grid of V1b as to utilize both stages at once?

I assume that running the output on V1a into the grid of V2b would also mean I would be removing the .1uf cap that is present at the grid currently...

Am I on the right page here or is this going to cause trouble?

[skid20]

lol I meant V1b into V1a... not thinking while typing = garbled nonsense!

[bob91343]

That would give you way too much gain. Why do you want to do this?

[skid20]

I'll be using it for guitar eventually, I guess I'm just going for one input more than anything. Would it make more sense to wire a switch between the to halves of the triode on a single input to change from one to the other?

Making it switchable sounds like a better idea to me in terms of guitar use.

If I set it up a three way switch that runs V1a or V1b or both (via one feeding the other or parallel) would there be a way to manipulate the gain in my favor?

[skid20]

[bob91343]

I just don't get what you want to do. What's wrong with the amplifier as is?

[skid20]

Originally Posted by bob91343

I just don't get what you want to do. What's wrong with the amplifier as is?

Its not a guitar amp. I intend on modifying it to be so. I'm just looking for a single input that is switchable between "channels" if you will..