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Fisher KM-60 schematics and mods

68.60.233.193
Posted on June 12, 2004 at 05:21:14
Scholl


 
I'm looking for the KM-60 schematics and anyone with mod sugestions.

The only mods I've made are changeing the 4 ceramic caps around the 12AX7 output tube with tin foil. From what I see the output stage uses a kooky class b type of bias.

For an experiment I built a general purpose pre-preamp with a 12B4 to use to replace output sections in various gear. The idea is to make a simple surgical patch around the output circuits into the outboard pre-pre so that the value of the original gear is preserved and output mods are what ever I'd want. But this experiment stalled out.

 

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Re: Fisher KM-60 schematics and mods, posted on June 13, 2004 at 17:36:43
Mike B.
Audiophile

Posts: 26356
Location: OR
Joined: September 27, 1999
Contributor
  Since: September 1, 1999
 the KM-60 is the kit version of the FM-50B. A excellent tuner IMO. I have a bunch and have used the Fisher Doc mod kit to improve their performance. It replaces the electrolytic, some film caps and a couple resistors. You will get some improved performance by replacing the two .1 coupling caps at the output tube with a 1uf high quality film. Do a search for the Fisher Doc website.

 

Re: Fisher KM-60 schematics and mods, posted on June 15, 2004 at 19:31:51
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 Any use of a 12AX7 as an output audio line stage puzzles me, even in CF mode the output Z is gonna be high.

If you have sufficient heater current reserve, even a selected 'good' 12AU7 should be an audible improvementeg an NoS 5814, even in CF mode!

Better still would be any other low mu high GM twin 9-pin noval triode, say a 5687 or any of the 6DJ8/6922/6N1P/6H30 family. If height inside the box is not an issue, a 6CG7 or an ECC99 would be great.

Otherwise yr idea of an external tube in stereo, bypassing the 12A-7 stage inside, should work well.


Timbo in Oz
The Skyptical Mensurer and Audio Scrounger
Peace

 

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