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

[Mike Morrow]

I wrote:

> The "tuning" of C6 is what Dave is doing now.  Of course, this
> arrangement is awkward.  It would all be unnecessary if an RF
> choke of decent value (like the common 2.5 mH RFC) and a .01 uF
> capacitor were substituted for the original two 23 uH chokes and
> 1000 mmF capacitor.  Then, nothing on the DC side of the filter
> would affect the RF side and the plate.  BUT...doing that would
> be too clever by half.  Some difference between receive and
> transmit frequency is necessary so that beat notes are heard
> between stations that just happen to be on the exact same
> frequency.

I should have included this remark to the above:

Since some offset in frequency, key open vs. key down, is necessary and desirable for CW beat note generation between stationz tuned to the same frequency, that makez choosing a value for C6 a lot less critical.  Instead of needing zero offset. now a several hundred hertz range is acceptable...whatever produces acceptable beat notes between several stations on a net.  That makes it likely a generic value like 500 mmf can be used in all sets.  Even though those sets will differ slightly in the offset caused by 500 mmf, the beat notes between those sets will remain acceptable.

Because a tube different from a VT-1 will likely respond differently to conditions on the DC side of the filter which affect the plate side, the original 500 mmf C6 may not produce the desired offset.

Mike / KK5F