[TMC] Pal 350/500

Wed Jul 21 13:20:09 EDT 2021

Thank you John!

I will look at the system drawings to see if I can figure anything out.

I am (relatively) certain that the power supplies were not turned on
and off every time a communication took place or data was transmitted.
That would be poor implementation and result in shortened lifespan
unless transmissions were very long with significant down time between
(unlike amateur radio). That leaves having the amplifier keyed on
biased to transmit 100% of the time for most of the variants. Some
variants did not even have the grids connected to pin 6 which would
have made the only viable way to operate them as keyed on 100% of the
time. Other variants that do send the grid connection to the power
supply terminate it in different ways, some which still result in
being keyed on all of the time as the only viable way to operate. I am
most curious about the particular PAL 500 variant that controls the
grids with the remote relay (as that is the power supply variant I
have). Is anyone aware of these amps actually being keyed by changing
bias with the remote relay in this manner?

Maybe I am thinking about this all wrong since they are designed for
100% duty cycle operation, what difference does it make if the tubes
are biased on all of the time other than more current draw? I am just
used to seeing final grids biased off during non transmit times, and I
ultimately want to use this for amateur radio and that is how I am
used to seeing it done. I imagine my Heathkit SB-220 would not live
near as long if it were biased on ready to transmit 100% of the time
it was powered up, but it wasn't designed to be biased "on" 100% of
the time.

If keying by bias change was actually practiced on some of these amps,
I would like to at least try. I do not want to significantly alter or
use these in a way that was not intended. I want to stick as true to
original functionality as I can.

Chris

On Wed, Jul 21, 2021 at 8:47 AM John Poulton <jp at cs.unc.edu> wrote:
>
> Chris,
>
> Welcome to the TMC list!  And, congrats on finding all three parts of a PAL-350/500.. so many of these beautiful amps have either gotten separated from their power supplies, or are missing their connecting cable, which is damn' near impossible to reproduce.
>
> Your keying question is an interesting one.  There are several folks on this list who operate PAL-350/500 amps, so it's likely one of them could advise the best way to key the amp.  But, if all else fails, TMC sold these amplifiers in various systems, like the SYM-1202/1203/1204 or "Shipboard Station", for example.  You might have a look at the documentation for these systems at:
>
> https://tmchistory.org/tmc_manuals/tmc_systems_manual_page.htm
>
> and perhaps dope out how TMC did the keying "officially".  Let me know if I can help in any way, such as chasing down TMC drawings..
>
> Best 73, John K4OZY (TMC "Librarian")
>
>
> On Tue, Jul 20, 2021 at 7:46 PM Chris Bolkan <bolkyboats at gmail.com> wrote:
>>
>> First, Thank you Nick England for getting me on this site and being
>> able to post!
>>
>> Hello! I am new to the list but not new to the admiration of TMC gear.
>> I used to stare at the TMC pages in the back of the ARRL handbook
>> catalog sections when I was a kid and wish I could have something like
>> that. Everything else in those pages paled in comparison. It was the
>> favorite equipment I wished I had and those pictures burned an image
>> in my brain that will never go away.
>>
>> Over the years I have acquired a straight GPR90 and an RXD which I
>> have used, held onto and displayed with great pride! Recently I
>> acquired a PAL350 amp and PAL500 power supply with interconnecting
>> cable. I am in the process of checking everything out, getting
>> acquainted, fixing the little things that were not right and starting
>> to power it up.
>>
>> To that end I have read every post in the archives of this list and
>> printed out everything that I think will be helpful in getting it up
>> and running properly.
>>
>> My first question has to do with the operation of these amps. I have
>> printed out schematics of the three 350 variants and the two 500
>> variants from the History site plus the instructions and addendums.
>> Studying these it appears that there are two (maybe 3) ways to "KEY"
>> these amplifiers.
>> First would be to turn the (HV) power supply on and off with the
>> "remote" relay circuit every time I want to key up, but I find that
>> idea unacceptable for obvious reasons, so I don't think that is the
>> way TMC intended them to be operated.
>> The second way I can imagine using it is to key the amp on (output
>> tubes biased to transmit) and have it resting in the biased on
>> position the whole time it is turned on ready to receive a signal from
>> the exciter to amplify. Is this how these amps were used with TMC
>> exciters? (which I do not have)
>> The third way to key the amp appears to have actually been an option
>> on one of the 500 variants, which was to use a remote keying signal to
>> change the bias of the output tubes from operate to cut off and back.
>> This seems to me to be the most logical way to do it. That way the amp
>> isn't keyed on 100% of the time, more like conventional amps I am
>> familiar with are operated.
>>
>> One concern to me is that the PAL 500 variant that appears to have
>> been sold this way seems to have an addenda to have the user reverse
>> this functionality bringing it back to the grids always being biased
>> on, removing the provision to bias them off from the remote relay in
>> the power supply.
>>
>> Any help and guidance is greatly appreciated.
>>
>> Thank you so much! I am sure more questions are to come and I hope you
>> all have patience with me.
>>
>> Chris Bolkan
>> KI7NXY
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