[ARC5] [Milsurplus] The Search for a Retubed, Stable BC-375

[Dennis DuVall]

Been running a stock 375 for over 20 years here.  In my experience the frequency drift is negligible on 160M, tolerable on 75 but a challenge on 40.  Most of the frequency drift seems to take place immediately following key-down while that huge oscillator plate heats up thus changing the capacity seen by the oscillator tank coil.  On 40m the frequency shift is about 3kc downward stabilizing after about 45 sec.  

One Idea I came up with but never  implemented was to somehow provide for a constant current flow through the oscillator tube, key up (not oscillating) or key down (oscillating) thus holding the physical  size/shape of the plate of the oscillator tube constant.  Never came up with a quick and dirty way to do this but might be worth a second look.

Dennis D.  W7QHO
Glendale, CA

***************

> On Nov 21, 2014, at 6:47 AM, Mike Everette via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> There was an article in one of the Surplus Radio Perversion Manuals about using a Command Set to drive a BC-375.  I also seem to remember a similar article from QST during the late 40s.  Someone on line has a BC-375 bibliography posted.  Might be Rich Post from Athens, OH (owner of the Boatanchor Pix site).
> 73
> Mike
> WA4DLF
> 
>      From: Robert Eleazer <releazer at earthlink.net>
> To: arc5 at mailman.qth.net 
> Sent: Thursday, November 20, 2014 8:03 PM
> Subject: [ARC5] [Milsurplus] The Search for a Retubed, Stable BC-375
> 
> Dave, why would you not use a pre-hacked SCR-274-N transmitter VFO in your BC-375?  We know that the oscillator will work with an FET with little modification.
> 
> Wayne
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