[ARC5] "Curing Chirp in Command Transmitters"

[J Mcvey via ARC5]

I am yet to get my transmitters up and running due to lack of time and materials. I am EXTREMELY curious if they will chirp or not. 
The only problem with any theory is the details. In this case, do we know how this gentleman was keying his transmitter? Was it modified or using the original equipment? 

I checked the transmitter diagram and amazingly, the only place they decoupled the LV line was with c61 because the the filament is part of the oscillator circuit for some reason ( anybody know?)and that is separated from the LV line via the series magic eye tube filament. No LV decoupling in the rack or MD7 either.


On Saturday, October 4, 2014 8:42 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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