Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on October 14, 2023, 10:00:34 pm

Title: plate fed tonestack master
Post by: joesatch on October 14, 2023, 10:00:34 pm
master placement difference between these two?  (imo nothing but not sure)

Title: Re: plate fed tonestack master
Post by: PRR on October 14, 2023, 11:45:19 pm
Tonestack usually likes to be fed from a low-ish impedance. Not the center of a 1Meg pot.

But it is just a couple wires to try it one way then another. Don't overthink too much.
Title: Re: plate fed tonestack master
Post by: sluckey on October 15, 2023, 05:39:55 am
I've never seen a C6 in that tone stack.
Title: Re: plate fed tonestack master
Post by: pdf64 on October 15, 2023, 06:23:55 am
Some people advocate putting the master before the tonestack, Jose style.
In theory it seems a retrograde move but I’ve not bothered to try it yet, so  :dontknow:

With regard to the right hand drawing, the DC blocking cap C8 seems redundant? Whatever, it’s in series with C11 the bass cap, and as they’re the same value, the effective valve of the bass cap will be halved.

And yes, the capacitive reactance of C6 and C9 the treble cap will form a high frequency potential divider / low pass filter.
Which end of the treble pot is intended to be the most trebly? Have you tried this?
Title: Re: plate fed tonestack master
Post by: PRR on October 15, 2023, 02:55:57 pm
I've never seen a C6 in that tone stack.

I've seen something *like* that in one of the recent amps that nobody loves.
Title: Re: plate fed tonestack master
Post by: joesatch on October 16, 2023, 09:56:24 am
I've never seen a C6 in that tone stack.
i tested values here. it removes some of the ice pick spikyness off the highs. Probably could be placed elsewhere
Title: Re: plate fed tonestack master
Post by: joesatch on October 16, 2023, 09:58:23 am
Some people advocate putting the master before the tonestack, Jose style.
In theory it seems a retrograde move but I’ve not bothered to try it yet, so  :dontknow:

With regard to the right hand drawing, the DC blocking cap C8 seems redundant? Whatever, it’s in series with C11 the bass cap, and as they’re the same value, the effective valve of the bass cap will be halved.

And yes, the capacitive reactance of C6 and C9 the treble cap will form a high frequency potential divider / low pass filter.
Which end of the treble pot is intended to be the most trebly? Have you tried this?

dont know why C8 is there myself. would be necessary in the left drawing but not the right
Title: Re: plate fed tonestack master
Post by: nworbetan on October 16, 2023, 11:12:06 am
I've never seen a C6 in that tone stack.
i tested values here. it removes some of the ice pick spikyness off the highs. Probably could be placed elsewhere

Most commonly placed as a bypass cap across the preceding anode resistor.
Title: Re: plate fed tonestack master
Post by: nworbetan on October 16, 2023, 11:19:45 am
Some people advocate putting the master before the tonestack, Jose style.
In theory it seems a retrograde move but I’ve not bothered to try it yet, so  :dontknow:

With regard to the right hand drawing, the DC blocking cap C8 seems redundant? Whatever, it’s in series with C11 the bass cap, and as they’re the same value, the effective valve of the bass cap will be halved.

And yes, the capacitive reactance of C6 and C9 the treble cap will form a high frequency potential divider / low pass filter.
Which end of the treble pot is intended to be the most trebly? Have you tried this?

dont know why C8 is there myself. would be necessary in the left drawing but not the right

My best guess is C8 is intended to be located close to the valve to keep the high DC voltage away from the tone controls on the "other side" of the chassis.