813 or something?

[w1vtp]

Geo

Well, this has been a good thread, I think.  I'd suggest two possible approaches.  First, investing a little more time in the scrounge mode and see what you can  come up with by way of a higher voltage PS.  I don't know if you frequent ham fleafests much but it would be fun to seek out something that would give you about 1200 - 1500 VDC @ 350 ma.  This would bring you into the ballpark of the higher power options.  '5HRO has made a good point about your current PS capabilities -- I encourage you to take some time looking for the components for something beefier.  Thing is that an "S" unit is ~6 dB  10 - 12 dB would be an excellent increase in power that would be quite noticeable.

You mentioned previously that you might be considering  other than plate mod.  That brings to mind my second option, I seem to recall my good friend Bob W1SET (recently SK) designed and built a 4D32 screen grid modulated AM rig that ran about 75 watts input.  That might be a good target first step for you to start with.  Just a thought.  I've attached some photos of Bob's xmtr - one I hope to restore to operation on 75

Good luck and good "hunting"  Al VTP

[VE3GZB]

Very VERY nice indeed!! I can see that the PA doesn't require a lot of watts to drive it....all of the other tubes are considerably smaller. Screen or Suppressor modulation is appealing for the reason that the modulation requirements are humbler....granted it's a bigger strain on the PA, but that's why I'd pick one tube to be strong to withstand it.

Well, I checked over the second power supply this evening, had to do some repairs before I powered it up. (See attached photo)

It uses only one rectifier - a type 80! Can you imagine! Such a massive power supply using such a vintage rectifier!

It's a choke input filter, output caps (the two grey rectangular boxes in the middle) are each 8uf 600WVDC.

Output voltage is 450VDC. AC RMS into the 80 plate to plate under idiling load (50K bleeder) runs 750VAC. Without the rectifier the plate to plate AC runs just a bit over 1200V (it just about pegs my Avometer, thank goodness I still have it, what a durabeast!).

The Xformer with the price tag (tape) on it is the HV Xformer. The one in the middle is only filament power. The black shiny box at the far end is the choke (it's value exceeds that of my LC meter).

This might be a good modulation power supply then, good for the 1625 to run in push-pull. The smaller power supply I tested yesterday, it delivers around 800 VDC no load, that might be good for the RF final! The Xformer on that one is a beast, it's actually deformed part of the chassis.

I can't afford to spend on big toys, I have to rely on what I can find via lowest possible cost.

There is still one power supply left...it's very VERY heavy and is in very rough shape.....most of the wiring is shot and I'd hate to rewire it just to find it's got some fatal flaw. I'll take it carefully on that one and see what it can do. One of the Xformers is on the verge of falling off the unit too, what a mess!

Oh well, that's life - if it was in good shape, it would be out of my budget.

[VE3GZB]

Final power supply, I've looked it over this evening. It's not as bas as I first thought, just some of the wiring was ratty. Caps Ohmed out ok and didn't draw strange currents when I fed them 50VDC. So I powered it up with a 100W bulb in series - always put a lamp in series when unsure - and with a pair of '80 rectifiers (yup, imagine!), 550VDC is delivered on the output.

After a bit of time, when it looks like it might be ready, I shunt the 100W series-lamp. Output jumps up to 950VDC and remains there, nice and steady!

WOW!