[ARC5] "Curing Chirp in Command Transmitters"

[Fuqua, Bill L]

  Does anyone have another example of a Hartley or Colpitts oscillator that has the filament at the same potential as
the cathode (RF wise)? Right off hand I can't recall one, not even the very stable master oscillators such as a VOX-5.
It is a 2-4 MHz oscillator that multiplies up to 64 MHz on the highest band. Used a 6C4 Colpitts oscillator and drift was on
the order of Hertz. Double Oven temperature stabilized. Unless there was something very strange about the 
1626 I just don't see it. 
73
Bill wa4lav
 
________________________________________
From: ARC5 [arc5-bounces at mailman.qth.net] on behalf of AKLDGUY . [neilb0627 at gmail.com]
Sent: Monday, October 06, 2014 12:30 AM
To: ARC-5 List
Subject: Re: [ARC5] "Curing Chirp in Command Transmitters"

Just quickly, if the original concept was for a directly heated tube,
there wouldn't be any cathode to heater capacitance. We meant
that they stuck with the Hartley-type cathode-to-tap circuit that
they had designed for the directly heated tube, but provided the
other winding for the 1626. We're both right.

73 de Neil ZL1ANM

On Mon, Oct 6, 2014 at 4:37 PM, Mike Morrow <kk5f at earthlink.net> wrote:

> > In regards to the cathode and filament circuit in the VFO of the ARC-5
> > tube.  It would appear that the circuit was originally designed for a
> > directly heated cathode tube and they decided to go with the 1626 instead
> > but not changing the initial design.
>
> No...it's the EXACT OPPOSITE of that.
>
> The 1626 MO tube being INDIRECTLY heated is THE ONLY reason behind this MO
> design that uses tapped MO coil T-53A and T-53B together as a bifilar RF
> choke.  This circuit puts the cathode and both sides of the heater at the
> same RF potential, and thus completely eliminates the effects of heater-to-
> cathode capacitance upon MO operation.
>
> Mike / KK5F
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