Various models of command receivers cover different frequency
bands.
For example:
BC453; 0.190 - 0.550 mcs. IF = 85 kcs.
BC454; 03.00 - 06.00 mcs. IF = 1.415 mcs.
BC455; 06.00 - 09.10 mcs. IF = 2.83 mcs.
And some other somewhat rarer models that cover 1.5 - 3.0 mcs.
and another the 'AM broadcast' band;
Circuit diagrams for all appear virtually identical; very minor
differences in component values (usually for the low frequency
BC453) and some use a 12SF7 instead of a 12SK7 as the second IF
tube/valve.
But can anyone advise if the tuning capacitors in these various
models are identical/similar???? Or a source for their mmfd.
values?
Got a BC455 (6 - 9.1) where someone has stripped virtually all
the plate off the tuning cap; in fact it will turn all the way
round (360 degrees) now! (maybe they were trying to bandspread it
or make a VHF version?) The tuning cap is under two layers of
covers so it appears to have been a careful and deliberate act!
Other wise the Rx. is pristine and unmodified! Any suggestions as
to why?
Following W.W.II many command Rxs. on the surplus market and in
connection with it, coils for replacement in the RF, Mixer and
Loc. Osc. so that they could modified to 12 volt AM/Medium Wave
car radios. The BC453 with it's 85 kcs. IF was also used by
amateurs as a Q5er to 'sharpen' selectivity.
BTW I've seen several command Rxs. where the miniature potted
headphone output transformer was burnt out when people have
modified the 12A6 output tube circuit to get more volume!
Any comments or suggestions would be most welcome. Terry.