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Old 24th April 2010, 02:01 PM   #1
skid20 is offline skid20  United States
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Default Bogen chb35a

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
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Old 24th April 2010, 03:29 PM   #2
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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
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Old 24th April 2010, 03:35 PM   #3
skid20 is offline skid20  United States
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Quote:
Originally Posted by rsumperl View Post
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
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Old 25th April 2010, 02:14 AM   #4
skid20 is offline skid20  United States
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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?
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Old 25th April 2010, 04:52 AM   #5
skid20 is offline skid20  United States
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lol I meant V1b into V1a... not thinking while typing = garbled nonsense!
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Old 25th April 2010, 06:26 AM   #6
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That would give you way too much gain. Why do you want to do this?
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Old 25th April 2010, 12:35 PM   #7
skid20 is offline skid20  United States
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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?
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Old 26th April 2010, 01:59 AM   #8
skid20 is offline skid20  United States
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Old 26th April 2010, 07:00 AM   #9
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I just don't get what you want to do. What's wrong with the amplifier as is?
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Old 26th April 2010, 12:23 PM   #10
skid20 is offline skid20  United States
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Quote:
Originally Posted by bob91343 View Post
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..
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