Versatile 300-600-900-1200 V supply with 115-230V transformers.

[IN3IEX]

Building experimental transmitters based on rare parts may be a risky adventure and you must keep alternative solutions in your design to solve potential future problems.
For instance I have a QB3/200 running at 1.2kV in my TX. May I switch to a 829B running at 900V or to a QE8/200 running at 600V in a fraction of a hour?
The answer is Yes... Why?
I have a multi-impedance modulation transformer and a multivoltage power supply, that can provide the full power on any of the outputs or a combination of them.
Here we use the last schematic of this paper:

http://www.ing.unitn.it/~fontana/Comparing%20Half.pdf

Most interesting are full wave multipliers, that (starting from 230V AC) can provide any DC voltage stepped by 300V in any combination.
You will notice that all half wave multipliers (except the lowest voltage in the first schematic) are capacitive coupled to the power transformer. This solution avoids DC current flowing through the power transformer (DC current must be zero in commercial power transformers).

For half wave multipliers it is possible to see that starting from 230V AC it is not possible to produce 300V without any DC current in the transformer (first schematic). The soultion is to double 115V AC (last schematic).
In the last two schematics a transformer with 115-230V secondary is used (230V center tapped secondary).
Remember that with capacitive coupling you can also add negative voltages to the chain, but you must accept a "doubler".


With abundant capacitance provided by common PC power supply capacitors (330 - 660 uF), you could take a couple of amper from any output, if the transformer can provide full power on 115V and 230V output. You do not need to know in advance where you put the load.

This solution has solved all my problems, including the commercial source for the transformer...

Giorgio


 

[The Slab Bacon]

Giorgio,
          One BIG problem is that in those type of power supplies you have NO isolation on / from the mains. This could cause a severe shock hazard, ground loop issues, and possible arc overs from anything in the circuits coming to ground.

So in transmitters you will have to isolate the chassis from ground and also keep the power ground and RF ground isolated from each other. You would have to feed them with isolation transformers in order to be safe.

the better choice would be to accumulate spare transformers and other hard to find items BEFORE you need them.

Back in the days of tube gear, we had radios and televisions with that type of power supplies. They were always shock hazards, especially if they had been serviced and the service tech wasn't careful of putting all of the chassis insulation back in properly.

Not to mention that it wouldn't pass safety standards here today.

[WA1GFZ]

1 good transformer and a variac makes life simple

[WD8BIL]

1 good transformer and a variac makes life simple

Even ifn you only variac 1 side of a 220VAC line.

[N0WEK]

Giorgio,
          One BIG problem is that in those type of power supplies you have NO isolation on / from the mains. This could cause a severe shock hazard, ground loop issues, and possible arc overs from anything in the circuits coming to ground.

So in transmitters you will have to isolate the chassis from ground and also keep the power ground and RF ground isolated from each other. You would have to feed them with isolation transformers in order to be safe.

the better choice would be to accumulate spare transformers and other hard to find items BEFORE you need them.

Back in the days of tube gear, we had radios and televisions with that type of power supplies. They were always shock hazards, especially if they had been serviced and the service tech wasn't careful of putting all of the chassis insulation back in properly.

Not to mention that it wouldn't pass safety standards here today.

As I see it from the text and schematics, he's just showing the transformers that he's using as generators. He's quite clear that he's using transformers from the line though.

[The Slab Bacon]

As I see it from the text and schematics, he's just showing the transformers that he's using as generators. He's quite clear that he's using transformers from the line though.

I must have misread it. The way I read it was that the only transformer he needed was the multi tap mod tranny and the rest came from the mains? ?

I went back and looked at his skizmatics again and he shows it coming directly from the mains. I reread his first post and it is unclear, but it seems like he is NOT using any type of isolation transformer.

Also I would not use 4000 series diodes in this (or any) application drawing much power. They tend to go to short if you just look at them wrong. I would much rather see 5400 series diodes and series a few up for redundancy.

Just my $.02 worth.............

[IN3IEX]

Hi. The words "commercial insulation transformer" appear in many places.
Normally I use 1200v 3A diodes. The kind and number of diodes is designer's choice.
The main subject of the message is obviously the circuit topology.

Just consider them for future designs.
Maybe they are convenient for many

The last one works very well for me.

I like to find new solutions....

Giorgio
 
 ... we have transformers in the title...

[Ott]

1 good transformer and a variac makes life simple

He is offering a more up to date white paper of sorts for obtaining a gaggle of voltages out of "1 good transformer and a variac"...  if one had the need and the parts, its another way to go about things...

[Opcom]

When I've done some of these kind of rectifiers, I have received poor regulation. The capacitor current can be very high and overheat it especially with electrolytics. I can't prove this but better luck was had when each stage before the final output capacitor C had a cap rated N*C of the stage before it.

so if it had 3 stages and the last stage was 50uF, the first stage was 150uF, next 100uF, then the 50uF one.

Most ever done was a voltage tripler for running six 6L6GC's so as to save weight. The regulation was bad and the 330uF input cap got so hot it smelled and I switched to a plate transformer as soon as one could be found.

Remember the old radio shack strobe tube? it used a voltage doubler and a 10uF cap as the discharge. I made a 9-tube strobe (was very bright) and used a 100uF cap for the first stage and even so it exploded after a while.

I don't remember why because it has been a very long time since doing anything other than a full wave doubler or the "4x8" (those seemed OK). The 4x8 looks something like the OP is trying except he is using more stages.

I think the troubles were to the repeating charging and discharging of the caps in the multiplying stages, but I want to study the circuits further; I certainly don't know everything.