I bought this amp back in the late 80's.
I think It was a 5c3.
The previous owner had the octal preamp tubes changed to novals.
There is also a mod that looks like a bias adjustment.
Is this there to adjust resistor value?
Can anyone tell me what this mod is and why they would do it.
This speaker is coded 220735 and C59103 P12R-C6103.
I am guessing that it is from the 60's.
Is this correct?
53 5c3 circuit changes
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53 5c3 circuit changes
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Re: 53 5c3 circuit changes
Looks like a bias balance? Trying to match output tubes/ get rid of hum. Don't think I have ever seen one like that on a cathode biased amp.
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Stevem
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Re: 53 5c3 circuit changes
Yes, it looks like a bias balance was added to better set the idling point of unmatched output tubes.
This means that each output tube should have a 1 ohm resistor added from pin 8 to ground so you can measure that current on each tube.
The speakers blue & silver label and date stamping says 1957 to me.
Somewhat unbalanced outputs can sound great for crunchy lead tones since more odd order harmonics are made by the clipping hard pushed output tubes.
It’s nice to have that added pot to experiment with as long as you do not idle one of the outputs too hot!
This means that each output tube should have a 1 ohm resistor added from pin 8 to ground so you can measure that current on each tube.
The speakers blue & silver label and date stamping says 1957 to me.
Somewhat unbalanced outputs can sound great for crunchy lead tones since more odd order harmonics are made by the clipping hard pushed output tubes.
It’s nice to have that added pot to experiment with as long as you do not idle one of the outputs too hot!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: 53 5c3 circuit changes
Thank you for your replies.
Re: 53 5c3 circuit changes
That's had a lot of changes by the looks of it, and that does look like a bias mod.
Its more likely a 5D3 since as far as I'm aware 5C3's had octal preamp tubes.
Its more likely a 5D3 since as far as I'm aware 5C3's had octal preamp tubes.
Re: 53 5c3 circuit changes
It did have octal tubes originally.