[TMC] Pal 350/500

Wed Jul 21 23:08:05 EDT 2021

Hi!

Here's my Pal 1k....

https://youtu.be/89RLnA0ozxE

73,
Prem

On Wed., Jul. 21, 2021, 10:57 p.m. triodes, <triodes at optonline.net> wrote:

> Chris, further to my comments about soft-start of the HV; unlike most
> commercial medium to high power transmitters,  my homebrew transmitter
> choke-input  HV PSU employs 66 uf of energy storage, with an operating
> voltage that can be variac controlled up to 3000 VDC. That's a lot of
> energy storage, and a near zero impedance as the capacitor bank charges up.
> With the soft-start,  I never trip the primary circuit breaker,  and
> there's no dimming of the house lights, etc., on key-down.If I recall
> correctly, my GPT-750 and PAL-1K rigs have something like only 15-20 uf of
> energy storage in the HV PSU as designed by TMC. I and all of the users of
> this well-engineered equipment have never had any reliability issues with
> them, whether the rig is keyed on via energizing the primary circuit of the
> plate supply, or some other form of enabling the key-on mode. Obviously,
> other factors such as turn-on and turn-off of the PA screen voltage, cold
> T/R switching, etc., in the correct sequence are other important concerns
> that have to be considered, as TMC invariably used common-cathode tetrodes
> in their IPA and PA stages, and not grounded-grid tubes as used in many
> amateur radio linear amplifier units. Particular attention to the
> protection of the screen, and application and removal of the screen voltage
> in the proper sequence in tetrode tubes must be observed.Good luck with
> this interesting project.73,Bruce, W2XR Sent from my Verizon, Samsung
> Galaxy smartphone
> -------- Original message --------From: Chris Bolkan <bolkyboats at gmail.com>
> Date: 7/21/21  10:21 PM  (GMT-05:00) To: triodes <triodes at optonline.net>
> Cc: John Poulton <jp at cs.unc.edu>, tmc collector's group <
> tmc at mailman.qth.net> Subject: Re: [TMC] Pal 350/500 Thank you Bruce.You
> confirming that it is/was standard practice to turn the HV supplycompletely
> on and off to key amplifiers is not what I expected. But itlooks like I'll
> have to get used to the idea! I have to admit thatthose big choke input
> filters would really limit inrush current(except for that to charge the
> magnetics depending on where the amp iskeyed on the 60 cycle waveform)I am
> still curious about the variant of the PAL500 that appears tohave been
> designed to key by changing bias on the final tubes fromoperation to cut
> off via the remote relay/switch on the power powersupply. Following the
> schematic of that variant, the filament switchturns on the filaments, the
> HV switch turns on the HV and the amp iskeyed by a relay that changes the
> final tube(s) grid potential betweenoperate and cut off. Would be awesome
> to hear if anyone is operatingthat version and could let me know how theirs
> works..... and if it isactually wired like that schematic or has been
> changed to key byturning on and off the power supply.I am going to dive
> into the system drawings that were recommended tome as my homework and see
> what else I can figure out.Thanks to everyone for the feedback so far. This
> is fascinating.Best regards,ChrisOn Wed, Jul 21, 2021 at 2:54 PM triodes <
> triodes at optonline.net> wrote:>> Hi John & Fellow TMC Enthusiasts!>> The
> issue of turning the HV on and off for PTT quick break-in operation should
> not create any fears, particularly if the primary AC circuit for the HV PSU
> includes a simple current limiting/soft-start circuit>> In my homebrew 2x
> 4-400A modulated by 2x 833As kilowatt-class HF rig, I soft-start the HV
> with a 10 ohm 100 watt resistor in series with the 240 vac primary circuit
> to the plate xfmr. After 500 msec, the resistor is shorted out of the
> circuit.>> The result is a complete lack of nuisance tripping of any
> circuit breakers, lights dimming in the house, etc. I built this rig 42
> years ago, and I've never had any failures of any of the power supply
> components, or any of the other components within the rig. And I'm still on
> the original RCA 833As, and my second set of 4-400As.>> I also soft-start
> the 4-400A and 833A filaments, to protect the filaments from  cold inrush
> current.>> Soft-start can be easily added to virtually any transmitter or
> amplifier without drilling any holes, etc., that would otherwise impact the
> originality of the equipment. A suitable power resistor, contactor, and
> time delay circuit are all that are required.>> By the same token, none of
> the variants of the 1000 watt output GPT-750 used soft-start for the HV
> on/transmit, and TMC obviously didn't think this protection was necessary,
> insofar as protection of the components and long-term reliability was
> concerned. Operating history in the field has confirmed their thinking was
> correct, but if you are concerned, add the soft-start capability to your
> PAL-350 rig. The plate modulated AM variant of the GPT-750, with it's PTT
> capability,  was probably the most stressed operation of this model
> transmitter, and they ran for decades with no record of out of the ordinary
> failures, etc.>> Just my thoughts....>> 73,>> Bruce, W2XR>>>>>> Sent from
> my Verizon, Samsung Galaxy smartphone>>> -------- Original message
> --------> From: John Poulton <jp at cs.unc.edu>> Date: 7/21/21 4:38 PM
> (GMT-05:00)> To: Chris Bolkan <bolkyboats at gmail.com>> Cc: tmc collector's
> group <tmc at mailman.qth.net>> Subject: Re: [TMC] Pal 350/500>> I have to
> agree.  Nick's absolutely right.. lots of ham rigs just slammed> the HV on
> and off by switching the primary voltage on the HV transformer> (but
> obviously not the rectifier filaments, if any)..   That whole idea> gives
> me the willies, though.. mainly because of the inrush current issue.> If
> the transformers hadn't been really inefficient, that problem could have>
> been fatal.>> I confess I've never thought about the keying problem for the
> TMC amps.  I> just had another (of many!) looks at the PAL-500 PSP-500
> schematic.  There> is, of course, a relay that controls the HV primary, but
> it's part of the> interlock system, and I'm virtually certain TMC didn't
> intend for it to be> used for keying.  I'm kinda thinking that the standard
> way that TMC keyed> these rigs was just to remove the RF excitation from
> the exciter, leaving> the amp idling.  The only issue with that is the
> (considerable) noise> generated by an idling linear amp, but in most
> installations, the amp, when> in standby, was isolated from the receiver by
> the antenna relay, so the> noise may not have been a bother.   But, that
> seems a little iffy to me as> well, in that the amp's antenna output is
> wide open.  What happens if the> RF excitation comes up before the antenna
> relay has a chance to switch over> to transmit?  Maybe it's just not a
> problem, given the robust design of> these amps..?>> In the 'standard'
> PAL-500, S206 switches the bias from CW to SSB mode, and> it seems to be
> the only circuitry that can mess with the bias.  If you'll> have a look at
> the schematics for PA and pwr supply, you'll see that the> bottom of S206
> goes to pin 6 of the power supply connector, and is involved> in CW mode.
> It is routed back to a relay in the power supply, K101.  This> relay's coil
> is connected to a couple of terminals labelled "remote PA> on/off".  I'm
> thinking THAT might be the keying system!  I can't quite see> how it works,
> but.. I think that's it.  A reading of the manual text may> help, if it
> describes what these terminals do.>> 73, John K4OZY>>> On Wed, Jul 21, 2021
> at 4:07 PM Chris Bolkan <bolkyboats at gmail.com> wrote:>> > I'm not trying
> to bait anyone with my comment regarding turning on and> > off the entire
> HV power supply just to key the amp. Maybe that is the> > way it is
> supposed to work. I'd be the LAST to know. It just doesn't> > seem like the
> best way to do it to me. I realize the power supply is> > choke input which
> helps a lot, but cycling something (almost anything)> > completely on and
> off every time it is used will shorten its life over> > just leaving it on
> or off.  Inrush current, charging and discharging> > those big caps
> repeatedly, the time it takes to charge and discharge,> > completely
> cycling the power through the ENTIRE circuit every time the> > mic button
> is pushed seems to me like a great way to shorten the> > system's life life
> compared to either leaving it biased on all of the> > time it is in use, or
> simply biasing the final tubes on and off.> > That's the way I see it
> anyway. I am only trying to learn and> > understand this stuff. It's the
> first of anything like this I have> > ever owned, and I want to make sure I
> understand as much about the> > intended operation as I can.> >> > And
> THANK YOU for having me! This type of discussion is exactly what I> > was
> hoping for!> >> > Chris> >> > On Wed, Jul 21, 2021 at 10:49 AM Nick England
> <navy.radio at gmail.com>> > wrote:> > >> > > OK, I'll bite - what's so bad
> about keying the AC to the B+> > > transformer? If I use PTT on my SBT-1K,
> that's what happens, Ditto for> > > all the 100-1000 watt AM transmitters
> I've come across. Don't know> > > about bigger rigs.> > > Granted I'm not
> experienced with SSB linears and have read you can> > > leave B+ on as long
> as you're not getting noise into your receiver.> > > Hoping to learn
> something here - -> > > Nick England K4NYW> > > www.navy-radio.com> > >>
> > > On Wed, Jul 21, 2021 at 1:21 PM Chris Bolkan <bolkyboats at gmail.com>>
> > wrote:> > > >> > > > 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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