[Milsurplus] BC-9: Is It Halloween??

[Kenneth G. Gordon]

I'm on the same page as you, Mike, and I also agree with Hugh that perhaps this thing never 
DID operate as it "should".

I think this is one of the most interesting discussions we have yet had on this forum, though. 
Thank you, David.

Ken W7EKB

On 19 Feb 2017 at 9:29, Mike Morrow wrote:

> I'd like to know what the set behavior is with that 3 mH choke added
> in series with the plate side of F.  If I understand Dave's
> description, this has not been tried.  It would be educational to see
> results after RF is effectively removed (with the 3 mH choke, and
> maybe a bypass capacitor) from the junction of the key and R5 and C5
> and F. 
> 
> It's obvious that RF is all over the place right now.  Choke it before
> it gets to the key just as an experiment to see what happens, perhaps
> even adding a bypass capacitor across the 1000 pF unit.  Who knows
> what the present characteristics are of that 95 year old device, both
> here and in the other F in the grid bias supply circuit? 
> 
> I'd like to see yet another experiment conducted without the added RF
> choke, but with known good 1000 pF capacitors in both F filters.  If
> that's been tried already, I missed it. 
> 
> Hue wrote:
> 
> >To try to replicate original operating characteristics, you must use
> batteries for all 4 voltage sources. No external supplies. >And, you
> must use a filamentary ( DC ) tube, no tube with a cathode. Because i
> think a certain amount of RF is coupled >back into the circuit via the
> filament. I think you're kind of chasing your tail, without setup as
> original as possible. 
> 
> Yes.  I would include in that originality restoration using the
> original 4600 kHz operating frequency, before attempting to operate
> the set at 3570 kHz (a change of 23 percent). 
> 
> It may be worth noting that the 4000 kHz BC-9 configured filter F
> differently than it is in the 4600 kHz BC-9-A.  The BC-9 has a
> capacitor connected to the junction of its two inductors that is
> omitted in the BC-9-A.  That suggests that there is some importance to
> the specifics of the design and frequency response of these
> filters...performance that may be upset by the attempted large
> departure from set design frequency or by F capacitor degradation or
> both. 
> 
> Mike / KK5F


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