[Milsurplus] BC-9: Answer One Question, Get Another.

[Kenneth G. Gordon]

I'd would be almost willing to bet they arrived at that "compensating" capacitor 
"empirically"..... :-)

Ken W7EKB


On 14 Feb 2017 at 4:14, Hubert Miller wrote:

> Dave, it's counter-intuitive as can be, isn't it?  The 'compensating capacitor' is always in circuit. And you'd think the components of filter F would pretty well isolate the tuned circuit -
> including tube plate and grid - from the power supply.  I looked at the filter components using the Shure Bros. cardboard swizzle, and the 23 uH chokes are about 500 ohms and
> the 0.001's are about 50 ohms each. Not perfect isolation, but you'd think good enough?  I am eager indeed to learn how well this 'compensating capacitor' works, assuming a good
> one is in the circuit. Hey - a funny thought just struck me - if that compensation idea has merit, you could try a mica compression trimmer across the battery here, and supposedly
> adjust for exact compensation. 
> 
> You have certainly contributed an outstanding brain-puzzler to the group!
> -H 
> 
> -----Original Message-----
> From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
> Sent: Monday, February 13, 2017 7:19 PM
> To: milsurplus at mailman.qth.net
> Subject: [Milsurplus] BC-9: Answer One Question, Get Another.
> 
> The mystery of the frequency shift appears to be
> solved:
> https://goo.gl/photos/Cp3hyLwEJmX3Ua3M7
> 
> But that brings-up another question:
> Just how does this freq. compensation work?
> The manual is available as a PDF at:
> https://drive.google.com/file/d/0B1zXYo8XYQS8MmgtNHVsektvT1k/view?usp=sharing
> 
> A simplified schematic is on page 19 (PDF paging).
> A full diagram is on page 20 (PDF paging).
> 
> It appears that the compensation cap, C6, when the rig is keyed, is connected one side to the Cathode circuit of the RF stage and the other, in series with the .001 cap in the Plate circuit filter, to the center of the Oscillator tank at the junction of
> the C1 caps.   So the effect is in
> the cathode circuit?  Anyone understand
> what's going on here?
> 
> 73 Dave AB5S
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