350k pot with tap

[Shack]

Somehow I bought one of these from Doug, not sure who messed up and dont care, but now I have one.....can someone shed a light on what they are used for and how useful....I know they were used in blonde and brown amps, but for what purpose?

[sluckey]

Treble pot in the 6G?? amps... such as...

https://el34world.com/charts/Schematics/files/Fender/Fender_bandmaster_6g7a_schem.pdf

[uki]

Old Fender amps use this type of pot, look at the 6G8 for example.

Here some pics

[PRR]

> for what purpose?

I believe the part was originally for (mono) Hi-Fi amp, volume control with 10% Loudness tap.

When mono hi-fi went out of style, Fender got them cheap.

[uki]

Here another example:

[st]

Here another example:

Pot in question doesn't have a center tap...

[kagliostro]

Ahem ....

Look to the left of the pot on the image

(DC voltage in from the rectifier)

Franco

[pdf64]

Compare the 6G7 and 6G7a tone stacks; the tapped pot allows the latter to roll off the HF response when set at / near minimum. With the former, when treble is set to min, the HF response stays flat at the level set by the mid resistor, unless the bass is turned up to max (I never noticed before that the 6G7 was like the Vox top boost circuit in that respect).
https://el34world.com/charts/Schematics/files/Fender/Fender_bandmaster_6g7.pdf
https://el34world.com/charts/Schematics/files/Fender/Fender_bandmaster_6g7a_schem.pdf

[st]

Ahem ....

Look to the left of the pot on the image

(DC voltage in from the rectifier)

Franco

I repeat, the pot that Shack was asking about, as opposed to the one in the schematic  posted by uki, does NOT have a ct (and is of a totally different value).

[PRR]

I think Uki posted to the wrong thread. There is another thread where bias-balance is being discussed.

[uki]

I think Uki posted to the wrong thread. There is another thread where bias-balance is being discussed.

Yes sir there is a topic about bias-balance as well where I did post that same picture ! 

I've posted this BIAS circuit as just an example of pot with CT , so Shack can have a broader view about the uses of pots with CT.

Pot in question doesn't have a center tap...

  It does ...

Magnify the picture so you can see, look at the left side of the pot/picture. There are 3 yellow wires, the one in the left side is going to the center tap of the pot.

[pdf64]

I think that the point being made is that there's a tap, but it's not a centre tap (ie it's a 100k tap on a 350k pot track).

[sluckey]

Pot in question doesn't have a center tap...

  It does ...

No, it doesn't. It has a tap but it is not a ***CENTER TAP***. The 350K pot has a tap at 70K. That's nowhere near center. That's pretty close to one end. For that 350K pot to have a center tap the resistance would be at half the resistance (175K). That's the point of st's argument.

Now the bias pot you posted does actually have a center tap. The 10K pot is tapped at 5K.

And my point is that just because there is a tap on a pot does not automatically make it a center tap. Kinda like a bias tap on a PT high voltage winding. It certainly is not a center tap. Or screen taps on an OT. They are not center taps either.


 

[sluckey]

(ie it's a 100k tap on a 350k pot track).

No. It's a 70K tap.

[uki]

(ie it's a 100k tap on a 350k pot track).

No. It's a 70K tap.

Thanks for clarify, I did miss the "center" detail.  I was aware of the tap not located in the center.

[MFowler]

From Martin Manning on Ampgarage