[HBR] Taming 6EH7 IF strip?

[Ian Wilson]

The IF strip appears to be working pretty well now. Numerous people had
helpful tips, all of which I think I followed. The things that made most
difference
were adding a shield across the tube socket to separate output and input,
adding shielding (nifty thin pieces of PCB cuttable with scissors) between
stages, and routing some long IFT leads over the ground plane instead of
in midair. The IF strip still oscillates with 100+22 ohm cathode resistors
but
is fine with 200 ohms, so will leave it that way.

The end-to-end voltage gain is about 28k V/V. However, some of this comes
from a 50 ohm matching network and some is lost in the mechanical filter
insertion loss. The overall numbers are in the same ballpark as the 75S3C,
which is what I am trying to emulate.

Things that people suggested that I added:
  - bypass heater connections at the socket
  - use twisted pair heater wires
  - use a VHF stopper resistor in the grid leads
  - use 2 decoupling capacitors in parallel
  - decouple power and AGC lines

I have added the BFO also. This leaked enormously to start with but with
rigorous shielding the output from the IF strip with no input is equivalent
to
about 5uV input.

73, ian K3IMW