[Milsurplus] GP-7 transmitter

[Jack Antonio]

On 2/27/2019 9:21 PM, W2HX wrote:
> I recently ran across a photo of one of these transmitters and it piqued 
> by interest. What are your opinions of this transmitter? How would you 
> compare it to, say, a TCS transmitter or a ATD (disregarding the multi 
> channel capability) or even the BC-375?

If you like operating a BC-375 or ATD, you will feel right at home with
a GP-7. Like the BC-375, the complete set of tuning units will take up
a lot of space. There is no provision on the transmitter for a local
microphone or key, and on/off control, those functions are provided by
the remote control boxes. There are two, the pilots and operators
boxes. The operators box provides the connections for sidetone to
an external receiver. The two boxes together with the transmitter
provide an interphone function. (Think pilot/gunner in an SBD).

At least one of the tubes (801) is an audiophile type tube, the
843 may also be an audiophile tube, as it is a directly
heated triode.

> I​'ve read it used 800 Hz power? Do hams build their own LV and HV power 
> supplies for this?

Providing power is the biggest stumbling block.

Building an external supply would require extensive modification.
High B+ is 2000V, plus multiple low voltage filament sources.

Providing 120V 800cycle takes effort. A rotary inverter takes
a substantial amount of DC power, and is acoustically noisy.

There are static AC power sources that run from 120V 60 cycle, these
are heavy, and can be a bit expensive, even on the used market.
Relatively inexpensive units do show up on eBay, but you have to keep
an eye out for them. In my case, I found a pair, in not quite the best
of shape, and making one good unit out of the two. They came from
Texas, so freight wasn't too bad.

I tried a PE-206 inverter, but it is an 80V unit, and required
a 400 cycle variac to get up to 120. It was OK for phone, but wasn't
capable of running full power CW, and was a bit chirpy due to
voltage regulation.

I was always a dollar short and a day late for a 120V 800 cycle
inverter, so can't comment on how well that works.

Also, there is a motor/generator set out there(not intended specifically
for the GP)that runs from 120V 60cycle, but it is very large and heavy
and probably not too common.

> Stability? Ease of maintenance? ease of use? fun to use? etc? I am not 
> sure I want to add one to the collection but it really has caught my eye.

Again, I rank the GP-7 on a par with the BC-375 as far as usage goes. My
unit has survived all my experiments with powering it, so I have to say
it is reliable. My GP-7 came to me pretty clean, the only issue I had
with the transmitter itself was a bad 803. My ATD, on the other hand,
was a very different story.

One last thing, when looking for GP parts and pieces, there were earlier
versions of the GP, that weren't exactly the same. They use different
tuning units, they look the same but don't interchange. I know the
GP-3 and 4 are different from the GP-6 and 7, but when the
change occurred, I'm not sure.

Anyone have a manual for a GP-3?

Jack Antonio
WA7DIA