Fisher Volume Potentiometer

[notdigital]

I recently picked up a beater 500-C to tke me through those lonely winter nights. A visual examination brought me to the volume pot which didn't seem right because it wouldn't mount securely even after trying to tighten the securing nut. Upon closer examination I saw that the pot plate closest to the face plate was not flat as is all of the pots I've come across. Deciding it was a repair replacement I removed it in favor of a replacement pot & switch I had on hand. The replaced pot had the correct Fisher part number BUT with a CX as a suffix. I guess it came from a CX pre? Anyone can confirm??

 

[dcgillespie]

Not -- Nope. All of the Fisher preamps use a dual loudness tap volume control.

Dave

 

[notdigital]

Not -- Nope. All of the Fisher preamps use a dual loudness tap volume control.

Dave

Aren't those the loudness taps?? The pot as I found it mounted is pictured below.

 

[audmod01]

notdigital;

Did the control with the problem have an indexing tab on it? If the indexing tab is not lined up with a corresponding hole in the panel it mounts to the control will be crooked with respect to the mounting plate. I have seen some controls that had a front plate that was made of cast metal that had a raised peg that fit into the indexing hole of the mounting plate. Others have a simple metal tab that can be bent. If the indexing tab was bent in the process of installing the control that could also cause the control to be incorrectly indexed or to not sit flush with the mounting panel.

Joe

 

[notdigital]

Naw Joe, the tab was fine. It's the build of the pot. Besides that, Tech Clippy figured that he'd not bend all the securing tabs of the pot all the way over to do something re mounting. He was trying to make the pot fit more securely or he simply forgot. I'll post a pic so all could see what I'm talking about re the front plate.

I was trying to find a Service Manual for the CX but there is none to be found. I figured that would solve the mystery.....

 

[dcgillespie]

Not -- The Fisher preamps have two loudness taps per wafer, for a total of four loudness taps on the control.
Dave

 

[notdigital]

Not -- The Fisher preamps have two loudness taps per wafer, for a total of four loudness taps on the control.
Dave

Ahhhh, then I guess the CX is ruled out! Thanks D

 

[notdigital]

Here it is Joe. I'm pretty sure I can replace the plate with a flat one and this pot will be good spare.

 

[dcgillespie]

Not -- The pic shows that your pot has the classic damage caused when the shaft (or the knob on the shaft) has received a significant smack, that drives the shaft back into the control when it was mounted in place. The result is that the front plate behind the brass mounting shank is now clearly bent (bowed). The front plate should be completely flat where is lies against the phenolic wafer, only being raised in two places to form a stop for the brass shank to keep it from turning within the front plate it is pressed into. You may be able to carefully push the front plate back into place. Otherwise, release the front securing tabs and remove the front plate and shank to flatten it back out.

I hope this helps!

Dave

 

[larryderouin]

Not. I usually take a 7/16 to 1/2 (which ever fits around the shaft hole and the raised area of the shaft hole)12 point deep socket, with the front plate on a flat surface and tap the socket with a small hammer leaving the raised area for the nut intact. If the plate rises up around the edge, just tap it with the hammer to flatten out. Once you get it all flattened out, re-install it on the pot.

 

[notdigital]

For future reference: I just came across a tidbit posted by the Fisher Doc regarding the "CX" designation in an auction item. Here it is in relevant part:

Fisher part No. R-50160-104. There is an "CX" suffix designation due to the modified power switch.

This control is from the very last production run from the late 1960's. Due to the issues with the power switches, Fisher changed to a different switch design using a single pole switch with a heavier current rating.