[BC] FM10K

[Bob Groome]

Some of the 10/20's had a non reactive resistor from the PA grid to ground as these boxes sometimes decided to oscillate and blow up things. Usually the bottom  1/3  of the band.

>From old notes: IPA Grid 8 to 10 mA
IPA Screen Volts 200 volts
IPA Plate Volts 2.5 kV
IPA Cathode 215 mA
IPA Bias  None
PA grid 10 to 30 mA
PA Screen Current 120 mA
PA Bias -250 Volts
PA plate 6.9 kV
PA plate 1.8 Amps

The PA tube socket had the built in by pass caps at about 7 and 8 o'clock looking down on the tube from the rear of the box; both Removed.
--
Bob Groome
cell: 916-705-0040
work: 800-476-8943
  

On Nov 11, 2013, at 9:58 AM, richardbrianjohnson at verizon.net wrote:

> A common problem with tetrodes and equipment that is "incompletely designed," is that vacuum tubes sometimes arc from plate to screen.