[AMRadio] Gates BC-1T


A.R.S. - W5AMI ars.w5ami at gmail.com
Mon May 7 10:10:05 EDT 2007


On 5/6/07, D. Chester <k4kyv at charter.net> wrote:
> "Now I'd be
> interested in what folks think, pro and con about the 1T.  I happen to
> think it's one of the neatest looking Gates in that power class."
>
> There is where you and I would have to disagree.  I think the BC1-T has to
> be the ugliest excuse for a broadcast transmitter ever made!  The epitome of
> its ugliness is that hump that pertrudes out, down at the bottom of the
> cabinet, under the door, over the grille for the air intake filter.  Also
> the ridiculous little triangular shaped viewing window.  If they had made it
> adequate in size and rectangular in shape, you would actually be able to see
> the 833A's clearly without having to move just to the exact correct position
> in front of the cabinet.  But mine didn't cost me a penny except for the
> trouble of picking it up and converting it, so I can't look a gift horse in
> the mouth.  Once I got it going, mine works very well.
>
HeeHee...  Well since you have one, I can't take any offense on your
idea of it being an ugly one.  I guess it's all personal opinion on
that aspect, but I do see your point Don.  it's sort of like a
bulldog.  Some of them are so damned ugly they are cute.  I know, I've
got one ugly/cute one ;)


>
> "I'd also like to hear from anyone that has tuned it to 160.  Will it go
> there without mods, other than re-tapping coils, etc."
>
> I changed out the fixed capacitors in the output circuit.  Scaled them all
> down proportionally from 1230  kc to 160m, and reduced the number of active
> turns in the fixed coil.   Whether or not you can just retune it depends on
> the original broadcast frequency.  I suspect you could just retune it if the
> original frequency was at the top end of the BC band.
>
This one was up there around 1250 so I suspect I'll have to do similar
to what you have for 160.  I also plan to get it on 80 meters later
down the road.


> I modified the oscillator unit in mine.  Changed the xtal oscillator stage
> into a grounded grid VFO buffer.  Grounded the control grid, disconnected
> the feedback capacitor from the cathode, and ran a coupling capacitor to a
> BNC  connector on the back of the osc unit to feed the VFO output to the
> cathode of the 12BY7.  It drives well with 50 ohms output from the VFO @
> about 200-250 milliwatts.

That sounds GREAT.  I ultimately want to use the Flex SDR-1000 as a
low power VFO/Exciter and receiver.  Of course the Flex can run up to
25 watts continuous duty, but I'd really like to get by with much less
RF drive.

>
> I removed the frequency adjust capacitors from the xtal oscillator, and
> mounted a variable capacitor with a real shaft  for a knob in the place of
> one of the xtal frequency adjust trimmers, and used that capacitor to tune
> the resonant circuit between the 12BY7 stages from the front  panel.
> Otherwise, you have to open the transmitter, remove the cover  from the osc
> unit, and take an insulated tuning wand to adjust the slug tuned coil every
> time you change frequency.  I had to remove about 1/3 of the turns  from the
> slug tuned coil to make it resonate all across 160m.
>
> Other mods: I modified the control circuit to run the relays on DC.  The
> a.c. contactor relays sound like a chain saw running, and nothing I did
> would quieten them.

Sounds like a good idea there too....

Also, I replaced the mod  reactor with a potted unit.
> The original one talked back so badly that I could just barely crack the mic
> gain before it started accoustical feedback.

That bothers me... maybe they are not all the same.  Mod reactors are
hard to find, especially potted, sealed ones.  I do have a spare RCA
reactor, 60hy @ 650ma, but it's open frame too.

I modified the cooling fan
> circuit to run them at half voltage.  They still run, and adequately cool,
> but make much less noise.  Originally they sounded like a vacuum cleaner
> running.  Basically, the transmitter was designed to be remotely controlled
> from the studio.  With the noisy a.c. relays and fans, and loud mod reactor,
> it was totally unsuitable to be located anywhere in the same room as the
> operating position.

Would the fan even be needed if you ran it at the 250 watt low power
position?  Likely not.  This one also has solid state rectifiers, so
no heat from down there.  At the 1KW setting, I wonder if four large
muffin fans somehow positioned to blow on each 833 would be adequate?


> I added CW capability to mine, but that's too long a story to tell here.
>
Don't plan to do that.  I'll use my Flex and Henry amp (if needed) for CW.

> Another change - I couldn't get enough grid drive for the 833A's in the
> final, even on the orginal broadcast frequency.  For 160, I replaced the
> original final amp grid /driver plate coil with one of similar size, made
> from air core (miniductor) stock, and that brought up the grid drive about
> 40%.  The original one is wound on a bakelite coil, using close spaced Litz
> wire.  It's probably OK for the lower frequencies, but I suspect 160m is a
> little too high for Litz wire to operate efficiently, plus the phenolic coil
> form is not exactly low-loss.

Another item good to know.


> Also, the driver/final stages with the 807's were squirrelly on 160.  I
> re-arranged the wiring in the final amp stage so that,  except for the
> output network components in the top of the transmitter, everything was
> grounded to one point on the chassis.  In the original circuit, they just
> grounded each component directly to the chassis at the point closest to that
> component.  Using the common grounding point made the final and driver
> stages much more stable.

Check.


>
> Another bit of flaky wiring that I corrected was that the rf output lead
> running from the oscillator unit to the 807 grids was completely unshielded,
> and integrated into the wiring harness along with the filament and d.c.
> leads!
That's hard to imagine!

I replaced that with a piece of coax, adding another BNC connector
> to the oscillator unit and soldering the other end of the coax directly to
> the 807 grid pins.  Someone told me that Gates eventually made an identical
> change in later transmitters.

I'll look for that first off when I get the thing.


Thanks Don, that will be a lot of help, and get me started.

73
Brian / wa5am



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