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Grid Choke

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Posted on February 1, 2017 at 13:34:42
sony6060
Audiophile

Posts: 696
Location: SE MI
Joined: August 8, 2014
If one does not have any grid resistors except the volume control at the preamp tube grid, has anyone tried a grid choke inserted at the volume control ground side?

 

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RE: Grid Choke, posted on February 1, 2017 at 14:41:23
dave slagle
Manufacturer

Posts: 4754
Location: NYC
Joined: April 27, 2001
the only place a grid choke could work wrt the volume control is from the wiper to ground.

dave

 

RE: Grid Choke, posted on February 2, 2017 at 05:56:54
sony6060
Audiophile

Posts: 696
Location: SE MI
Joined: August 8, 2014
I wire the volume pot signal input to the pot 120K and ground the other side. The wiper is the input to next stage. So, would not the grid choke wire in-between the pot ground end and ground to lift any AC shunting to ground?

 

RE: Grid Choke, posted on February 2, 2017 at 06:02:27
dave slagle
Manufacturer

Posts: 4754
Location: NYC
Joined: April 27, 2001
No.

If you wire it that way the grid choke will be a frequency dependent impedance in the shunt leg of the voltage divider.

The artip of the series vs the shunt values of a voltage divider determine the attenuation of a pot. If you put a fixed inductance in the ground leg you will mess things up pretty badly.

dave

 

RE: Grid Choke, posted on February 2, 2017 at 06:05:43
sony6060
Audiophile

Posts: 696
Location: SE MI
Joined: August 8, 2014
I think I will not install a grid choke. Thanks Dave.

 

How about a grid choke that has multiple taps..., posted on February 2, 2017 at 10:43:51
Chip647
Audiophile

Posts: 1653
Location: The South
Joined: December 24, 2012
and get rid of the volume pot all together. Possibly something like a switchable signal level autoformer for level control?

 

RE: How about a grid choke that has multiple taps..., posted on February 2, 2017 at 10:53:04
sony6060
Audiophile

Posts: 696
Location: SE MI
Joined: August 8, 2014
Never thought of a transformer as a volume control.

 

Transformer Volume Control (TVC), posted on February 2, 2017 at 11:03:14
BenM
Audiophile

Posts: 40
Location: British Columbia
Joined: January 22, 2001
Transformer volume controls have been around for many years now. If you do an internet search, you will find many examples for diy. They are pricey though. I purchased a Stevens and Billington tvc years ago and installed it in my 26 preamp.

 

Autoformer Volume Control (AVC), posted on February 2, 2017 at 11:16:13
Tre'
Industry Professional

Posts: 12022
Location: So. Cal.
Joined: February 9, 2002
might be even better.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Grid Choke, posted on February 2, 2017 at 20:24:31
Michael Samra
Dealer

Posts: 35577
Location: saginaw michigan
Joined: January 30, 2005
Contributor
  Since:
June 24, 2005
Dave
Depending on the DC resistance of the choke,cam't it change the effective resistance of the volume pot to where it may not operate as it's supposed to,going from the wiper to ground?

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Grid Choke, posted on February 2, 2017 at 22:04:38
dave slagle
Manufacturer

Posts: 4754
Location: NYC
Joined: April 27, 2001
For AC the inductance of the choke appears in series with the DCR and the combo becomes part of the load the volume pot needs to drive.

At some low frequency the finite inductance will indeed cause problems but that needs to be analyzed on a case by case situation.

dave


 

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