• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Mystery tube in a Fisher FM-90X - V50,064

After checking out the schematic for the FM-100 from gingertube's response I came up with this, an Amperex (or Valvo) 6922 PQ, late 50's.
It has the gold pins & pinched waist described in this link: http://spazioinwind.libero.it/themagicsound/_private/6922pinch_waist_eng.htm
The only markings on the tube that I can read is the "52F", which you can see in the picture. There is a fainter marking that I think is "46L" but I'm not sure. Maybe a date code?
What do you think?
 

Attachments

  • img_0215b.jpg
    img_0215b.jpg
    63.6 KB · Views: 187
john q. bebop said:
After checking out the schematic for the FM-100 from gingertube's response I came up with this, an Amperex (or Valvo) 6922 PQ, late 50's.
It has the gold pins & pinched waist described in this link: http://spazioinwind.libero.it/themagicsound/_private/6922pinch_waist_eng.htm
The only markings on the tube that I can read is the "52F", which you can see in the picture. There is a fainter marking that I think is "46L" but I'm not sure. Maybe a date code?
What do you think?

I can verify for sure it is a late 50's Amperex 6922 Pinched waist.
This is the "cascode" tube in the Fisher Golden Cascode circuit. It was an innovative RF amp circuit that was also used in many later Fisher tuners. I also have an FM90X here. Funny thing, I bought it a long time ago, and then bought some Amperex 6922 pinched waist tubes (cheap) to use as exact replacement spares. Many years laterI find out this is the holy grail tube for many people, worth big $. :)

Bob