[TMC] 750 help thanks

[Albert Santangelo]

Hey Jay,

Good luck on getting your 750 on the air. Sounds like some of the other guys
on the list have given you a lot of assistance as well. This list is great
for that.

I have a GPT 750A2/URT-17, which I have converted for high level plate
modulated AM.

I've had it going for almost a year now, and for the last 9 months, it has
been very reliable. I homebrewed a 3-400z class B modulator, driven with a
modified Eico 730 modulator driver. I have bypassed the driver/modulation
transformer on the Eico, and am using a Hammond  1707, 60watt class B driver
transformer, from the plates of the EL34s in the Eico, to the grids of the
3-400zs. The Hammond driver transformer has a split secondary, and it is
tapped in from each end, so I could use a tapped screen/triode connection on
the EL34s. I use a 5.6 volt zener diode, bypassed with a 50uf 50v
electrolytic cap, in the filament ground return for the 3-400zs, for
regulated bias. The modulator tubes idle at about 80ma, and are very easy to
drive.

No problem making in excess of 800 watts of carrier, with full modulation.
This is legal here in the Great White North..
Problems in getting mine going for the most part had to do with reversing
some modifications done to the buffer/RF driver section, done by the
previous owner. It was as difficult to figure out as working on a receiver,
and not having any written documentation of these mods. Lots of e-mailing
with the previous owner needless to say.

My m/o drifts a bit and is out of calibration, but its fairly stable for the
mode I run it in.
If you look inside the RF section at the meter compartment containing the PA
Plate, Multimeter, and the RF current meter, you'll see that the PA Plate
meter has full B+ across it, or in my case, modulated B+. I had a bit of
arcing occurring from the connector studs at the back of this meter to the
back of the meter compartment. There really isn't enough of a gap there, so
I sandwiched in a piece of that insulating pressed phenolic board, between
the backs of all the meters in there, and the back of the meter compartment.
Arcing has been eliminated.

The RF output connector is a type HN or UG-560/U, and you shouldn't have too
much trouble finding an adaptor or connector for it, to mate with RG/8. I
found one at a hamfest.

The problems that I encountered in first getting the transmitter on the air,
were related to the incomplete information in my manual for the routing of
the screen voltage to the RF final amplifier in the AM mode. Got that info.
and we were away to the races. Pretty easy band switching here between
160/75/40meters.

Hope this was of some help to you Jay. Let us know about your progress in
getting the transmitter going.

Al Santangelo  VE3 AJM

Jay Roman wrote:

> Thanks Doug, Todd and Roy for helping me here on my 750.  I have most of
> the documentation.  When I bought it I got the manuals directly from
> TMC.  Don't know if they do that any more.  I was thinking of bypassing
> the TMC MO for my Collins triple oven time standard that is in one of my
> URC32s. So both receiver and transmiter are on the same clock.
>
> Roy asked what the RF out connectors are.  There are two on the right
> side of cabinet, the "test" connector which is a so-239 and the main one
> (can't remember the number at the moment) that is much larger.  So, I
> think I'm good for RF out.
>
> I'm interested to know opinions on operation.  It looks like it is a bit
> of a chore to change freqs and bands during operation,  perhaps a little
> harder than my KWS-1.  Maintenance looks to be fairly easy.  Aside from
> URC32s or KWT-6s I have never seen a xmitter that has "all access" like
> this.  Overall, I would like to use this on a regular basis if it's not
> to hard to get around with.
>
> Thanks for all the help and I' sure I have more questions!
>
> Best 73s
> Jay Roman
> KB0ATQ
>
> _______________________________________________
> TMC mailing list
> TMC@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/tmc