[ARC5] "Curing Chirp in Command Transmitters"

[Tim]

Hi Les - Or maybe it was a simple case of RF getting into his VOM metering
wiring and tricking the meter movement ..It happens  LOL
Who's to know.

Tim
N6CC

On Sat, Oct 4, 2014 at 5:42 PM, Leslie Smith <vk2bcu at operamail.com> wrote:

>   Hello Dave,
>   If this theory is correct - that RF is entering the filament leads
>   from OUTSIDE the transmitter - then adding a balun externally  to the
>   filament lines should prove/disprove the theory.
>
>   The remedy (shielding the filament wires) cures the problem (according
>   to Mr. Cline) but surely the shielded wires dissipate RF energy in the
>   shielding.
>   My strategy would be to keep the RF "out" by some other means - see
>   the following:
>   Given that the filaments were originally wired in a series connection,
>   and Mr. Cline measured 12 volts (and 18 volts when transmitting), I
>   suspect the filaments had been re-wired.
>   If your theory is correct, then the RF power getting into the filament
>   lines is wasted power - about 2.7 watts per "tube".
>   (i.e. (18 x 0.45) - (12.6 x 0.45) per tube.
>   Power heating the filaments isn't reaching that magical substance
>   called "ether".
>
>   All this is speculation on my part - I don't have a set to make
>   measurements, but it's speculation informed by maths.
>
>   73 de Les Smith
>   vk2bcu at operamail.com
>
>
> On Sun, Oct 5, 2014, at 10:38, Dave Merrill wrote:
> > 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
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