|[AMRadio] Update on BC-1T|
SBJohnston at aol.com
SBJohnston at aol.com
Mon Mar 5 00:04:12 EST 2007
As I reported earlier, the substitute BC-1F modulation transformer is working
nicely in my Gates BC-1T. Over the week I replaced the loudly buzzing
contactors with some 240 VAC units bought new on eBay for a few dollars. They're
This weekend I modified the oscillator/buffer stage to choose between three
sources: VFO, Xtal 1, and Xtal 2. This was as easy as bending up a tab stop
on the rotary switch to allow it to access the next contact. I added a BNC
jack to the side (bottom when mounted) of the osc/buffer cabinet for the VFO
For coverage of 160m, I also took half the turns off the buffer tank coil,
and changed the tank cap to one with with a shaft. I extended that with a
non-conductive shaft that sticks up through the top (side when mounted) with a nice
knob. This lets me peak up the buffer for full band coverage. Crystals are
on 1885 and 1985 kcs.
The driver stage was in range of resonance without mods, even at the high end
of the 160 band. Any higher and the coil would need to be changed a bit
Drive was excellent and the PA tuned up as easy as could be. Neutralization
wasn't hard either. Everything acted as expected.
It sounds sweet on a receiver across the room - maybe a little too much
low-end. This big mod transformer might be helping there. I need to proof it to
find out what's what. The 833 modulators are glowing just right, although I
do see some idle current drift after they've been working for a while.
My audio chain is either a D-104 into my 12AX7 mic preamp, or a flat dynamic
mic into Behringer mic processor with EQ, into a Logitek rack mixer, into a
DAP-310 processor. A CD player is also fed into the mixer so I can run test
tones easily from disc instead of a signal generator. All rack-mounted and
raring to go.
The next steps are to key the low B+ in step with "Plate On/Off", add PTT
action by removing the latching connection on the plate control relay, and
antenna TX/RX switching. Oh, and figure some way to enclose the outrigger mod
transformer so the dog or cat doesn't get killed (or me). I'll be on the air
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