Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 72Blazer on June 09, 2023, 06:26:48 pm

Title: 6G6B Treble Potentiometer Question
Post by: 72Blazer on June 09, 2023, 06:26:48 pm: Is there anything special about this pot? I see it is a 350k pot but The 70k Tap has me confused.

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Title: Re: 6G6B Treble Potentiometer Question
Post by: sluckey on June 09, 2023, 06:49:05 pm: Quote from: 72Blazer on June 09, 2023, 06:26:48 pm
Is there anything special about this pot? I see it is a 350k pot but The 70k Tap has me confused.
Yes. It has a 70K tap. That means four lugs. That also makes it special.

It was used for a short time during the reign of the 6Gxx amps, then abandoned. Hard to find now so that also makes it special.
Title: Re: 6G6B Treble Potentiometer Question
Post by: HotBluePlates on June 09, 2023, 07:54:21 pm: Quote from: 72Blazer on June 09, 2023, 06:26:48 pm
... I see it is a 350k pot but The 70k Tap has me confused. ...

WeberVST must have paid Alpha a long while back to re-make those pots. AFAIK, they are one of the few (only?) places to find a 350kΩ pot tapped at 70kΩ (https://www.tedweber.com/wp354at/)
Title: Re: 6G6B Treble Potentiometer Question
Post by: 72Blazer on June 09, 2023, 08:10:51 pm: Thanks Sluckey and Hot Plate.

Confirm this would in fact work?
Title: Re: 6G6B Treble Potentiometer Question
Post by: PRR on June 09, 2023, 08:31:25 pm: It is an old MONO loudness pot. When stereo arrived, these were a bit of a glut on the market. Fender found a use, good for them, but it is a historically dead-end part. And not easy to fake. Get the Weber part, while you can, IF you think this tone-network is what you want. It IS made for the Fender application.
Title: Re: 6G6B Treble Potentiometer Question
Post by: sluckey on June 09, 2023, 08:40:02 pm: Quote from: 72Blazer on June 09, 2023, 08:10:51 pm
Thanks Sluckey and Hot Plate.

Confirm this would in fact work?
What do you think?
Title: Re: 6G6B Treble Potentiometer Question
Post by: 72Blazer on June 10, 2023, 07:35:02 am: I'm gonna give it a shot. Thanks all.
Title: Re: 6G6B Treble Potentiometer Question
Post by: AlNewman on June 11, 2023, 12:06:33 pm: I see tapped pots quite often in radios where they combine a volume and tone circuit.

How does this example work? Is it basically a standard fender tone stack, until the treble hits 20% rotation, then the two caps work in parallel providing a bass boost?
Title: Re: 6G6B Treble Potentiometer Question
Post by: pdf64 on June 11, 2023, 01:30:04 pm: It facilitates a treble cut http://www.guitarscience.net/tsc/brownface.htm#RIN=38k&RT=350k&RB=250k&RTap=70k&R1=100k&R2=6.8k&RL=1M&C1=250p&C2=100n&C3=100n&C4=5n&RB_pot=LogA&RT_pot=LogA
Title: Re: 6G6B Treble Potentiometer Question
Post by: AlNewman on June 12, 2023, 08:55:01 pm: That is pretty interesting. Must be suited for jazz or something.
Title: Re: 6G6B Treble Potentiometer Question
Post by: tubeswell on June 13, 2023, 12:37:47 pm: Quote from: pdf64 on June 11, 2023, 01:30:04 pm
It facilitates a treble cut http://www.guitarscience.net/tsc/brownface.htm#RIN=38k&RT=350k&RB=250k&RTap=70k&R1=100k&R2=6.8k&RL=1M&C1=250p&C2=100n&C3=100n&C4=5n&RB_pot=LogA&RT_pot=LogA (http://www.guitarscience.net/tsc/brownface.htm#RIN=38k&RT=350k&RB=250k&RTap=70k&R1=100k&R2=6.8k&RL=1M&C1=250p&C2=100n&C3=100n&C4=5n&RB_pot=LogA&RT_pot=LogA)

That’s a cool interactive plot. Thanks for posting.