[AMRadio] Update on BC-1T

[SBJohnston at aol.com]

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 
silent.

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 
input.

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 
though.

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 
soon...

Steve WD8DAS






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