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.

Back in the mid fifties I got a BC-455 and modified it for 10 meters by
removing most of the plates from the rotor of the tuning capacitor plus some
other things but I can't recall, too long ago. It worked quite well but was
insensitive so I had to add an RF preamp and then it was a champ. The 10
meter mod appeared in QST or CQ. So try yours out on 10 meters and see what
happens.
73
hank wd5jfr
"Terry" wrote in message
...
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.

In article , Terry
writes:

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.

That unit had a CBY number-only used by the Navy, IIRC

and another the 'AM broadcast' band;

BC-946

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.

Yep. The IFTs and RF coils are plug-in, too. It's clear that a basic Command
set rx could get quite far down the assembly line before a decision had to be
made about what range it would cover. And if a set got shot up in combat, a lot
of its parts could be used to keep other units going.

But can anyone advise if the tuning capacitors in these various
models are identical/similar????

They're all different.

Or a source for their mmfd. values?

BC-455 is 62 uuf per section. BC-454 is 142 uuf per section. I think BC-453 is
365 uuf per section.

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?

Bandspread and/or tuning range.

There were all sorts of mods to improve the bandspread and change the tuning
range of those rxs. The IF of the BC-455 is so high that it would be OK for 10
meters and maybe even 6. Since the RF coils are in a removable plugin unit,
they could be played wit fairly easily.

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.

Yup.

They could also be used with crystal-controlled external converters. A really
good 80/40 receiver could be had by putting a simple crystal controlled
converter in front of a BC-453, using the '453 tuning. Inexpensive nonhamband
suplus xtals do the heterodyne job (4050 for 80 meters, 4300 for 75 meters,
7550 for 40 meters, etc.)

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!

Yep. That little transformer is a really good one but it's not meant for 3
watts of audio. btw, the original sets are meant for 4000 ohm loads while the
-B models can be used for 4000 ohm or 300-600 ohm loads by moving one wire on
the output trans.

73 de Jim, N2EY