Assistance with power supply wiring please

[Blair]

Hey guys,

I'm playing around with a few power supplies I found on the net with some spare parts. Can someone please explain how I would wire this one using a multi section cap. I see how it works, but I'm having a great deal of difficulty seeing it on a multicap.

I have a 20-20-20-40 multicap. I know it isn't exact, but close enough right Yellow_Light_Colorz_PDT_02

Here is the link to the scematic:

http://www.bonavolta.ch/hobby/en/audio/12au7lin.htm

Thanks,

Blair

[TomMcNally]

Blair -

You can't use a multi-section cap in that circuit.
It's a voltage doubler, and C-1 is above ground.
You're better off with separate capacitors, because
you could only use sections for C-2 and C-3 ...
no use for the other sections.

[Ty_Bower]

You can't wire that up with a multi-section cap. It's a voltage doubler circuit. The multi-section caps have all the negative leads of each section tied together to a common ground (the can itself). You need a separate cap where the negative isn't tied to ground (C1, in this case). If you try to wire up that circuit with a multi-section cap, you'll end up with a few hundred volts shorted to ground. At best, you'll blow a fuse. At worst, you'll burn up the transformer.

Sometimes you'll see an old tube radio with a cardboard wrapped cap. That's a sure sign of a voltage doubler. You could do it without one of those cardboard wrapped caps, but you would still need two separate caps, and you'd need to make sure that one of them doesn't accidentally short to the chassis.

Edit... yeah, what Tom said... (beat me to it)

[Blair]

Thanks guys,

I did as you said, and I'm getting about 185v instead of the 265v, but I
m only using one of the B+. Is this right, or do I need to drop the dropping 6.8K resistor? I'm just playing around, but are these typically quiet circuits?

Blair

[Shannon Parks]

Hi Blair,

So you wired it up per the schematic (using an isolation tranny I presume?) and now you read 185V at C1 before the dropping resistor?

[Blair]

Hey Shannon,

I don't know what the voltage was before the dropping resistor. I had company show up before I could play around with it. I assume it is an isolation tranny. It is 120v at 200ma with a 2A 5v winding.

I was using my variac to tinker with it. I suppose it can't hurt to pull the dropping resistor out completely considering I am looking for another 80v or so at least. I'm just not sure whether to pull the 12K or the 6.8K.

Blair

[Blair]

Is there anything wrong with using these types of circuits? After actually reading up on it, it seems like an extremely good solution for lower current power supplies. Most driver tubes don't pull that much so if you had a 100ma tranny, and you use a voltage doubler, you end up with 50ma available right? This is sufficient for amlost any common Driver tube right? Sorry for all the questions, but before I blow the garage up, I'd prefer to have a bit of more refined advice.

Thanks,

Blair

[EWBrown]

In a voltage doubler, the current has to be divided by two. So a transformer with a 200 ma rectified DC rating, the doubled voltage will have a maximum capability of 100 mA, etc... Rob Peter to pay Paul.

I've used vltage doublers in some lower powered SET amps, with good results.

I've seen this type of PSU circuit used in moderate power amps, as well, 18WPC, X 2.

I have a power trannie of unknown heritage (may be H-K) that has an HV secondary 140VAC around 400 mA, and two 6.3VAC, 3A windings.

In a doubler circuit, it should deliver around 360-370 VDC with a 150 mA load, about perfect for a stereo 6BQ5 / EL84 amp.

HTH

/ed B in NH

[Blair]

Thanks Ed,

I'll play around a bit with it. I have access to a few more of these 125v trannys. The parts are cheap enough. Why not.

Blair

[EWBrown]

In my small 6S4 SET, I use a heathkit 54-59 trannie (from an old TV color dot / bar generator) which has about 130 VAC winding with around 300 mA capacity (I could feed a 40 watt lightbulb with it delivering 120 VAC output) , and a 6.3 VAC filament winding around 4A capability.

FWIW, the original Heath circuit also used a voltage doubler, with 1960s vintage silicon rectifiers and 2X 100 uF can caps. Under normal operating conditions this delivered a B+ of 306VDC with about 50 mA loading. THe "hot" can cap was mounted on a fiber mounting washer, and the can was sitting around 153VDC (and yes, it could bite the unwary). In those days, safety wasn't a major factor... Not only did they not use a fuse in the AC primary circuit, there were hot can caps that were far too easy to come into casual contact. Yhe metal covers were a must, when using these, if one wanted to enjoy a long and healthy life...

I used a voltage doubler with this (same as in the "Abraxas" amp) with 2 uF4007s, two 470 uF / 220 V caps, then through a 15H choke, iwhich has a DCR of 411 ohms, nto a 100 uF / 450V cap.

Unloaded, the B+ is around 360VDC, and drops to around 300VDC with a total load of approx 55 mA (and and around 340V before the choke).
I also full-wave bridge rectified the filament voltage.





/ed B in NH

[Blair]

Cool deal. I think I follow you. time for the broom stick for the power switch trick Yellow_Light_Colorz_PDT_05

Blair