[TMC] Pal 350/500

[W2HX]

Welcome aboard! We all have caught the TMC bug so we can all convalesce together!
Eugene


-----Original Message-----
From: tmc-bounces at mailman.qth.net <tmc-bounces at mailman.qth.net> On Behalf Of Chris Bolkan
Sent: Tuesday, July 20, 2021 7:45 PM
To: tmc at mailman.qth.net
Subject: [TMC] Pal 350/500

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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