[TMC] WTD: K-701 for the GPT-750 RTM modulator

[James M. Walker]

Hi John,
What you are looking for is the relay from a Johnson matchbox,
which is also the relay from the modulator deck on the BC-610 (I)
and others, and also the relay that is on most of the older high power
RF Amps for low VHF, VHF, and UHF on the GE 4EF1 series
of rigs.

That info ought to enable you to shake one out of the trees!
73
Jim
WB2FCN


----- Original Message ----- 
From: "John Poulton" <jp at cs.unc.edu>
To: <TMC at mailman.qth.net>
Sent: Wednesday, January 24, 2007 7:28 PM
Subject: [TMC] WTD: K-701 for the GPT-750 RTM modulator


> Folks,
>
> I'm attempting to restore a type RTM modulator for the GPT-750,
> and I'm in need of a part.  I'll describe what I need, then run
> on at more length about the restoration, in case anyone is
> interested in the details I've learned so far.
>
> The part that's missing is the CW/Phone relay, K701.  It's a quite
> heavy-duty relay with 10A (non-inductive) DPDT contacts, and a
> 10,000-ohm, 150VDC (15mA) coil.  The pix of the relay in the
> GPT-750 manual closely resembles the Advance Relay type AT antenna
> changeover relay.  I happen to have one of these, pictured at:
>
> www.jptronics.org/pix/ATrelay.jpg
>
> And it does fit perfectly in the modulator.
>
> If any of you have any of:
>
> 1.  Another Advance Relay type AT (mine is usable, but the ceramic
>    base is broken)
>
> 2.  The exact replacement relay with the unusual high-impedance DC
>    coil (a very, very long shot!), or
>
> 3.  A 10,000-ohm, 15mA coil that I can use to replace the one on
>    my relay--it's about 0.73" tall and about 1.475" in diameter,
>    but anything close could be made to fit,
>
> 4.  Another similar relay with the right contacts and coil, OR
>
> 5.  An entire junker modulator (yeah.. right!),
>
> I'd be willing to pay very reasonable $$ for it.  I also have a bunch
> of TMC oddments that I'd be happy to trade for a suitable relay.
>
> ---
>
> As many of you probably know, the GPT-750 had at least two incarnations.
> The modulator I'm trying to refurbish is clearly from an early 
> transmitter.
> It's front panel is 13-3/16" tall, where the later middle-drawer panels
> are 14" tall.  It has only two captive screws to secure the panel, and
> they're quite small, rather than the 7 large screws on later panels.
>
> The main power connector on the rear apron, J701,
> is of a different type than the later transmitter.  I'm pretty sure I
> can solve this problem.  The GPT manual sez the TMC part number
> for this connector is MS3102A-28-11P, which of course is the Amphenol
> part number, so I'm hoping to find one of these at William Perry Co.
>
> In addition to the dimensional differences, the front panel of this
> modulator has been brutally hacked.  A second meter hole, which looks
> as if it had been bored with a hole saw, is located directly under
> the Modulator Plate Current meter.  Oddly, there's a nicely engraved
> panel label that says "Plate Voltage" right under this hole.
>
> In any case, I'm planning to fabricate a new panel from scratch.  It'll
> mate up with the captive hardware on the later GPT-750, but have a hole
> pattern to accept the chassis and front-panel handles for the early
> modulator.  Already have the 'technology' for painting the panel and
> getting it screened, thanks to some excellent local vendors.
>
> Other than the mechanical and connector differences, it looks like
> this modulator is just like the later RTM-2's.  If any of you have
> any thoughts or experiences to share re these modulators, let me know!
>
> Anyone out there know where to find the captive hardware for the panel?
> If I can't find anything that matches, I'll just fabricate new hardware,
> but that'll be a day's work.  Oh, but wait.. a day in the machine shop!
> There's no downside! :)
>
> Thanks much, and 73, John K4OZY
> -- 
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