Changing resistor/caps question...a little help?

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Mondoslug
Posts: 33
Joined: Mon Apr 21, 2008 10:44 am

Changing resistor/caps question...a little help?

Post by Mondoslug »

I'm curious about changing values of the resistor/caps as it specifically relates to tone, or feel, sag etc. or any of those other extremely subjective factors. IE: higher number value equals less bass, etc etc. Can these generalizations be made at all?

So up or down for the following results in what as related to tone. I know it's not that easy but just wondering if there are some real basic generalizations. TIA!

Slope resistor.

V1B cathode Bypass

V2B Cathode Bypass

Resistor feeding OD trim pot

Power tube socket screen resistors.

Resistors on the Power Supply board.
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Structo
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Location: Oregon

Re: Changing resistor/caps question...a little help?

Post by Structo »

What circuit are you using?
Tom

Don't let that smoke out!
Mondoslug
Posts: 33
Joined: Mon Apr 21, 2008 10:44 am

Re: Changing resistor/caps question...a little help?

Post by Mondoslug »

Hi...it's the Ceriatone Overtone. Thanks.
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heisthl
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Location: Phoenix

Re: Changing resistor/caps question...a little help?

Post by heisthl »

Mondoslug wrote:I'm curious about changing values of the resistor/caps as it specifically relates to tone, or feel, sag etc. or any of those other extremely subjective factors. IE: higher number value equals less bass, etc etc. Can these generalizations be made at all?

So up or down for the following results in what as related to tone. I know it's not that easy but just wondering if there are some real basic generalizations. TIA!

Slope resistor.

V1B cathode Bypass

V2B Cathode Bypass

Resistor feeding OD trim pot

Power tube socket screen resistors.

Resistors on the Power Supply board.
Slope - bigger = more preamp gain because less signal is going to ground but this change affects the response of the mid and bass controls. Play with the Duncan tone stack calculator.
Bypass caps - quite a dramatic change in tone shaping of the stage because is boosts the low end - typical values are 1uf, 4.7uF, 5uF, 10uF and 25uF - with 25uF being the fattest. The danger is sending too much bass into the OD section which makes the OD sound too brassy.
OD entrance resistor - resistors pass lows better than highs, so bigger = more lows, but it also reduces the overall signal level which can mistakenly sound like you're reducing lows.
Screen resistors - smaller = more gain but less tube safety factor against excessive screen grid current, don't go below 470 ohms on 6L6 or 1K on EL34's.
Dropping string resistors - Very dramatic changes to amp tone, rule of thumb is around 300v on phase inverter plates (or 250v if using the blues master PI), 190 - 210 on the OD(V2) and 180 - 200 on the preamp (V1). Lower plates = smoother and less harsh, but there are no absolutes. This is the best place to start before doing any other tweaks.
Former owner of Music Mechanix
www.RedPlateAmps.com
Mondoslug
Posts: 33
Joined: Mon Apr 21, 2008 10:44 am

Re: Changing resistor/caps question...a little help?

Post by Mondoslug »

Wow....thanks so much for that. Very concise. I almost understand it. 8) :P Seriously thanks.
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