[ARC5] "Curing Chirp in Command Transmitters"

[Dave Merrill]

One of my 'finds' at Shelby last month was a 1947 edition of "Hints and
Kinks for the Radio Amateur."  In the 20 page "Converting War Surplus"
section, I found the following:

<begin quotation>

Curing Chirp in Command Transmitters
Alfred Scott Cline, W6LGU

My BC-459-A chirped and from what I've heard on the air, most everybody
else's does too.  I tried various methods of keying, and extremes of
voltage stabilization, but the chirp persisted.

Checking with a good v.t.v.m. showed 12.6 volts on the filaments with the
key up, but from 18 to 22 volts when the key was closed!  The added voltage
was r.f.

To remedy this situation, shielded filament wire was substituted in the
rig, with by-passes at each end of the wire.  Old microphone cable (with
high r.f. losses) seemed best.  A heavy copper strip was run across the
chassis and the "cold" ends of the 1625 filaments and the cathodes were
connected to it to get a good ground.  This change resulted in chirpless
keying for me and has done the same for all the others to whom I have
passes this hint.

<end of quotation>

Okay, I know Command Set keying chirp has been beat to death but perhaps
this is still worth discussing.

W6LGU does not mention how he is keying the BC-459-A which might be helpful.

Even without this information, my suspicion is the unwanted r.f. is coming
from unshielded filament leads OUTSIDE the transmitter.

Thoughts?

73,
Dave
N9ZC