Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SolidStateCircuitReject on November 12, 2017, 09:22:25 am
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Hi Folks.
Sorry do not know the proper term for this part of the circuit, but after v1b coupling cap there is a series of capacitors and I'd like to know the function. Image attached.
So I know what caps in series and parallel do, but there is obviously a hole in my understanding. So after the coupling cap between V1b and the gain/volume knob there is a shaping circuit where there is a 470pF paralleled with a .0022µF cap. The circuit then goes on to seemingly bypass the volume pot with a parallel set of .0047µF and a .001µF... and these are in series with another set that contains a 470pF in parallel with a 120pF bypassing the 470k (grid resistor I think? or mixer?) going to v2a.
My logic tells me that I can summarize this to roughly .0027µF in series with a 590pF bypassing the 470k resistor... but I somehow think there is more to it and I am missing something???
Can anyone explain to me?
Thanks!
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I think commonly available values were paralleled to give a non common value. For example, you can easily find a 470pF and a 120pF. But can you show me a link to a supplier that has a 590pF?
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I think what they've done is taken a particularly good sounding original 1959SLP and measured it. They're replicating the measured values with parallelled caps.
So it's effectively still the original circuit with a coupling cap, a treble bleed cap on the volume pot and then a treble bypass on the 470K mix resistor.
I guess they're having to measure the caps they're using, given the tolerance of them, and choose ones that match the values on that schematic.
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Thanks!
Okay so I didn't have a hole in my understanding. Great!!!