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Anyone out there with one of these currently using it on the air?

?Just got my home brewed power supply finished using the Drake L-4B plate transformer (wired for 240VAC) , voltage doubler using (2) Semtech 5000v diode stacks and Harbach (SB220) 8x330uF board.




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73/Rick
W4XA
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Rick and Gentlemen,

I hope to answer yes in a few days. I collected one just this Saturday.
Worked a 13 hour shift yesterday(Sunday). Have to snail mail the balance of what I am paying for it this AM.
Hope to get some time for a detailed inspection later today and will post findings.?

I am surprised at a 3kV plate supply bundled in with the rest of the wires in the power supply cable. 1964 :-) !!
Manual says it's OK for the 3-400Z to idle with 120mA Ip. 360W idle on a 400W tube. A shack warmer for sure.

73, -bob ah7i em73ts Atlanta GA

A'hem.....

I think I am going to need a picture of this to believe it!!

Halli put a 150ohm resistor in the cathode circuit to reduce the idling current to 40mA or so. (select/deselect with the T/R relay via the jumper terminal in the back of the RF deck)

The whole reason for that was to provide current to get the swinging choke to "swing" because it needed a minimum of 55mA or so.?

210k bleeder @14.2mA plus reduced idling 3-400 @40mA and the choke would "choke"......without that swinging choke action, the voltage was 4000-4500V (capacitive input voltage for a full wave + 6750 CT secondary)

This is the main reason I completely rebuilt the power supply using the Drake L-4B plate transformer plus capacitor input filter.

They literally used the reduced idling current as a power supply bleeder!

Once you have a PSU that doesn't need a lot of bleeder current, you can change that 150 ohm resistor to a 15K resistor effectively cutting the tube off during STBY/receive

If I had it to do over (and had a higher voltage PW Dahl $500 transformer) I would use it to get about 3500volts!

When I tried 3-400's in my Drake L-4B, (At L-4B plate voltage) they performed identically to the 3-500's

With my "new" HT-45 power supply, running on 240VAC line voltage (245V) I was seeing 600W output from loudenboomer.

I made my own "cable".? The only voltages in the cable (except the HV) are 120VAC.? The HV wire I used is solid core ignition wire that is probably good for around 20kV or more.? No problem with it inside the vinyl hose I put it all in.

I also installed an 8-pin jones plug (like the L-4B uses)




Made the mount for the jones socket out of thick phenolic

Then added a 240V power inlet for the power cord.


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73/Rick
W4XA
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I am also a proud owner of a Loudenboomer, but it has been many years since power was applied to it.
I need to recap the power supply. I don't want exploding capacitors and magic smoke. This is an original
Hallicrafters power supply for the amp, and original owner (W8DCL Walt-SK) rebuilt it 25+ years ago.
I love the mods, the jones plug and all, and may do the same to mine.
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73 de w8nsi Jim
TS480SAT, Hallicrafters HT45 Loudenboomer Mk2 amp
80m loop, 40-10 efhw, 4BTV vertical, Tennadyne TD-160

If you're using the original swinging choke input supply, remember that you cannot "test" it unless you have it connected to the amp or you add additional bleeder..

I wouldn't use the amp(for testing)? until I know for sure everything is ok in the PSU.?

An easy way to do it is to temporary install additional bleeder resistor(s) in the power supply to approximate the reduced idling plate current of around 45-50mA

If your power supply is original, it should do somewhere around 3000v.? The original bleeder is 210k

I=V/R ? or 3000/210000 = approx 14.3mA?

So you need around 45mA or so additional draw on the power supply to get the swinging choke swinging!? (Halliscratch did it with the final tube in the amp when the "jumper" on the back of the RF deck was in place)?

The additional resistor needs to be in parallel with the 210K

?For 45mA.......R=V/I or 3000/0.045 or roughly 67K?
AND since it's going to get pretty hot, it needs to dissipate some serious power.? P=Vsqr /R? Or 3000 * 3000 /67000 = 134W

Or if you prefer I(squared) * R ?? (0.45)SQR x 67K

Since you're not leaving it powered for long periods of time, you can use lower power resistors for short periods of voltage measurement.? You could even use? 50K resistor but the current will be higher and it's important to use 67K because this approximates the 40-50mA the tube will draw in standby

USE? A HIGH VOLTAGE PROBE, I got this one:
BK PR 28A 40kV High Voltage DMM Probe

I think I gave about $40 for mine.? I know they're more expensive now.? But don't skimp on something that could end your life!!


Hook everything up and stand back! then throw the switch.? (keep one hand in your pocket!!!)

If you try to test it with the amp and the (idling) current draw is low (below that which would make the choke work properly)? for some reason, the plate voltage could likely exceed 4000V and destroy the meter, oil capacitor and other components in the amp...... so it's imperative that the power supply is "right" before you hook up the RF deck



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73/Rick
W4XA
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Thanks for tips Rick!
Nice job on yours.

Working on mine has been delayed by a broken tooth. I'm hoping to play with it by Saturday.
Serendipitously picked 15k and 50k 100W resistors at the same hamfest! Have a Heathkit high voltage probe.
The 866As were replaced with a pair of solid state rectifiers. It looks like that's as far as? it went because the
new HV is not connected to anything and there's no visible damage. I'm hoping all is good.?

I acquired this HT45 thinking It will make a nice 6m conversion. Got it home and decided it's too nice.?

73, -bob ah7i em73ts "boil your water" Atlanta

Hi Bob,

Yeah, mine had a shorted rectifier filament transformer.? (HV arced to ground at the bottom)?? The transformer still produces the voltage required for 866, 3B24 etc but I think if HV is turned on it will follow the carbon path!!

Most have replaced those tubes with diodes anyway!?? I was worried the same might happen with the swinging choke eventually so I started looking for a way to eliminate it.? When I first powered mine up I saw 4500V on the meter thinking it was somehow defective until I put the HV probe on it.

Turned out I had a broken (nearly invisible) solder joint on the resistor board bolted to the 3kv oil filled capacitor!

The poor/broken joint effectively took the bleeder resistors out of the circuit.? If you have insufficient bleeder, according to the ARRL handbook, the output voltage "soars"? (their words!!)? It absolutely "soared"!!

Putting 4500V on the 3000V oil cac wouldn't last long either!? ..........remarkably, the oil cap was un-damaged!? (they're really MUCH better at handing over voltage than any electrolytic ever could be!!)?

It's amazing how many old amplifiers out there (Hallicrafters, Johnson, Henry, etc) have nearly irreplaceable swinging chokes & rectifier filament transformers that are just waiting to go "POW"!!

And it's no wonder that amp builders and manufacturers eventually moved away from rectifier tubes and? swinging chokes.

Don't get me wrong, a swinging choke in an HV power supply (properly designed)? has excellent voltage regulation (better than cap input) but they work fine with the slightly less effective regulation of a capacitor input supply.

Having said all that, if you can cobble up enough resistance to approximate the 55-60mA needed for minimum choke current, you can easily test everything without the amp connected.

I also tried an Eimac? 3-500 in my HT-45 and it did fit ok.?

When I get everything together, I'll try it again to see how it performs but I'm not all that concerned because I have 3 good 3-400's.? Those will very likely? last until my kids send this stuff to a landfill!



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73/Rick
W4XA
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Hi Rick and readers,

Had a little time this AM to study the supply.

If I understand the RCA ham tips article: he 200K 50W bleeder, if the only load, gives ~10% ripple. That puts 3300V peaks on the paper cap that's rated for 3kV.?
I'm OK if it fails, there is the fuse, and can replace with modern polyester film caps.

I'm curious if adding some C will increase the peak current in the HV transformer. For anyone who has not seen one, the original transformer has big radiator fins! Operating at full ratings, it's making at least 100W of heat.

I'll fire it up with 12 V AC? to verify ripple and max voltage with the 200k. With only 12 VAC on the primary, there is still close to 1 kV on the transformer secondary (P to P)!?

Any reason to not move the swinging choke to the center tap lead and get the high voltage to ground off of it?

Speaking of unobtainable parts, I also have a Johnson Thunderbolt. I was keeping an eye out for whichever bit of iron is bad for so long that I forgot what it needs. Poor thing has been on a little furniture dolly under the bench for over 30 years :-).?

RF deck? Something is rattling under the chassis. But, the top looks good. Will get to it once the supply and HV interconnect is sorted out.

Using the Duncan Amps power supply designer (/g/duncanampspsud)
I modeled the factory supply with 866As, with diodes, and with different bleeder and capacitor values.
Long story short, everything other than design values increase transformer/choke current, HV, or both.?

Took bottom cover off the RF deck and found:
Rattling to be a small nut and washer that do not appear to be part of the amp; RF deck filament transformer good; 3-400Z heater continuity, Grid not shorted; Ig and Ip metering resistors are open(Ig resistor blown open :-); Meter works; Lots of dust, dirt, and cat(?) hair.? Hope to find some suitable 0.25 ohm resistors in the junk box.

HP45:
10k resistor for the HP45 NE51 lamp is missing.?
Hope the tube is not gassy.
Use the ~10kV P to P transformer secondary with some current limiting to check for gas in the tube? Why not!

What to do once working?
Move RF deck fuse holder to HP45 chassis and use that hole for a HV connector to run HV+ with wire that's good for at least 3kV.
Assemble TR relay(s) with 'PTT' keying circuit for tube bias as suggested in manual.


73, -bob ah7i

Thanks for posting that article!? That stuff never changes with time does it!!


The original transformer is rated at 6750 (CT).....so with 12V the secondary should yield 675(RMS)? and Yes.....? The peak would be right up there too!. (With 12v RMS, the peak is about 17V)

I know there are many high voltage plate supplies that have placed the choke in the CT.? It actually is a pretty good way to reduce the total voltage on the choke.? Doesn't do much for the rectifier filament transformer though.

Don't forget to post pictures!

We love pictures!

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73/Rick
W4XA
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