[HBR] Re: GB> RSGB Keyer: I QUIT!!!

[Ian Wilson]

Ed,

I know first-hand how frustrating it can be to get an apparently
trivial circuit to work. I suggest with this one you give it a day
or two to cool off (better than hurling it against the wall).

I looked for a similar circuit, and found it in the 1962 Handbook,
p252. The oscillator part is identical apart from trivial circuit
value changes, and use of a 12AU7 rather than a 12AT7. So I
don't think there are errors in your schematic.

I would next check some basics:
  - continuity of transformer winding and tap
  - DC resistance of transformer (should be R from each end to tap,
      and 2R between ends)
  - 12AT7 heater correctly wired for 6.3V (pins 4&5 connected
      together; 6.3VAC present between pin 9 and pins 4/5)
  - DC supply: should be about -85V no load (120V transformer
      and halfwave rectifier). Note polarity: + side of supply is
      grounded, and - side isn't
  - check voltages on oscillator tube pins:
      pin 1 = plate. With key down and RATIO pot set to middle,
         should be some -ve voltage. This should vary as you vary
         the RATIO pot
      pin2 = grid. Should be -85V (or whatever the supply is)
      pin3 = cathode. Should be somewhat less negative than
         the voltage on the grid
  - try a different tube. The resistances in this circuit seem quite
       high to me, perhaps your 12AT7 is a little gassy
  - check for corrosion in tube socket. Wiggle the tube (a little)

If all this fails, send me the thing and I'll see what I can do.
(I can cheat, since I have a keyer here that I suspect uses a
similar circuit to yours).

73, ian K3IMW