Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on November 11, 2022, 05:24:23 pm
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In this badcat schematic theres a 470k across the gain pot which according to the math would basically just change the 250k pot to around 160k. Can't be there for that reason, so Is there some other reason for it and if so what?
https://schematicheaven.net/newamps/badcat_hotcat_30.pdf
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that appears to be exactly what it's doing
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I know, but i find it odd. 250k as about as low as i have seen for a gain pot so i find it odd the would wanna lower it that much. And if there is a reason i'm curious what it is.
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Pure speculation...
The amp was built without that resistor but it was a little too wild. So the builder experimented a bit and discovered that adding that resistor tamed the wildcat just enough to be acceptable.
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Bearing in mind the 1n5F coupling cap, the 470k will roll off more low end.
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https://schematicheaven.net/bargainbin/valco_510-1b.pdf
This is the lowest gain pot I've ever seen in a tube amp. 100K
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I think having the 470K in parallel would change the effective taper of the Gain pot?
That said, that probably wasn't the designer's main intent.
Ed
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I think having the 470K in parallel would change the effective taper of the Gain pot? …
No, the resistor would need to be connected to the wiper for the taper to be affected.
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My guess would be that he found that 250k allowed too much gain after fining the design that sounded best except for the excessive gain and decided to tame it a bit that way. Thats what I recently was fighting with but tried that and wasn't thrilled with the result. But my guess is he liked it but rather then incurring the extra cost of having 160k pots made he just did it this way.
Thats my speculation because from the replies it seems thats all it accomplishes. And if so, cost would be the only reason not to have custom pots made. Adding a 2 cent R is a lot cheaper and makes for a far easier repair scenario.
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Bearing in mind the 1n5F coupling cap, the 470k will roll off more low end.
Why would he want to roll off more lows with a small coupling value? Just curious.
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Bearing in mind the 1n5F coupling cap, the 470k will roll off more low end.
Why would he want to roll off more lows with a small coupling value? Just curious.
I doubt that was even a consideration. You think too much... :icon_biggrin:
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Bearing in mind the 1n5F coupling cap, the 470k will roll off more low end.
Why would he want to roll off more lows with a small coupling value? Just curious.
I doubt that was even a consideration. You think too much... :icon_biggrin:
Tell me about it ! I'll fix that tonite with beer if only for the night.
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I'm way ahead of you. :occasion14:
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I'm way ahead of you. :occasion14:
You're a better man than i.....either that or you're on the east coast. :laugh:
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I think having the 470K in parallel would change the effective taper of the Gain pot? …
No, the resistor would need to be connected to the wiper for the taper to be affected.
Oops. I was thinking about another matter, i.e. how to modify the 5E3 to get to the DeArmond R15 / Martin 112 design, where the Volume pots are 350K, and 350K pots are not readily available.
But we don't have to go there right now. :icon_biggrin:
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... I was thinking about another matter, i.e. how to modify the 5E3 to get to the DeArmond R15 / Martin 112 design, where the Volume pots are 350K, and 350K pots are not readily available. ...
500kΩ is "close enough."
There's nothing particularly special about the DeArmond/Martin amp: it is a tweed 5E3 Deluxe with some different pot-values. It's not gonna be materially different from any other tweed 5E3 Deluxe.