[robster]

Hello Fisher 400 tube reciever owners,the two 12ax7 tubes directly behind the dial glass,that's the preamp section right? what's the function of each tube in this section. I think it's V8 V9? not sure I don't have a manual. just the 2 closest to the dail glass up front. I have 2-5751's I would like to put in those spots.

Cheers,
Robert

 

[Hirsch]

One is the gain tube, and the other is the tone control.

 

[robster]

Many thanks!

which is gain and which is tone control?

Cheers,
Robert

 

[Hirsch]

OK, I was hoping to answer without having to look for the schematics, but I found them

Looking at the receiver from the front, V8 and V9 will be to the far left behind the glass. These tubes are the phono stage (also used to amplify tape head input).

The voltage gain is controlled by V10, and the tone controls go through V11 (these are the main "preamp" functions). The drivers/phase inverters for the power tubes are V12 and V13. Besides the four power tubes and the tubes mentiond above, all of the other tubes in the receiver deal with the FM receiver/multiplexer.

 

[robster]

Many thanks!!

Cheers,
Robert

 

[nblis]

If you have a 400 with a serial number between 10001 and 29,999 then tubes 9 and 10 are the preamp tubes, and changing these will alter the sound characteristics of the amp. You can find further discussions on Audio Asylum in the vintage section. I put two nos fishers in mine and it did make a subtle difference.

Noel