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Homebrew HT Bench power supply.

 
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Homebrew HT Bench power supply.

Post by GlowingAnode » Tue Aug 18, 2015 10:04 pm

I was chatting to Andy (Dr. Wobble) via pm about a bench power supply I built a few years ago using a mains transformer from a Tektronix 545A 'scope.
I thought I'd done a write up, but couldn't find one so thought I'd add some photo's for interest.
Two HT ranges, 100 - 300 V and 250 - 450 V. Will push 200 mA all day, a bit more briefly.
2 x 12E1 series regulator, EF80 error amp. Silicon rectifiers.
Attachments
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Re: Homebrew HT Bench power supply.

Post by Pamphonica » Tue Aug 18, 2015 10:56 pm

Very nice. A properly meaty supply! And good use of that nice blue professional Veroboard.
Jeremy

 
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Re: Homebrew HT Bench power supply.

Post by Refugee » Wed Aug 19, 2015 3:21 am

I have just started collecting bits for one. It will be made of silicon so it will have to go in another thread.

 
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Re: Homebrew HT Bench power supply.

Post by Dr Wobble » Wed Aug 19, 2015 7:30 am

Thanks Rob, nice job. Why did you use valves for regulation ? Hi fi nuts will be salivating over the 12E1's. Any chance of a schematic for those like me who arn't as knowledgeable as yourself.

Andy.

 
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Re: Homebrew HT Bench power supply.

Post by Cathovisor » Wed Aug 19, 2015 7:57 am

The Farnell E350 uses either one or two EL34s: other PSUs I've seen use 6080s whilst another I have uses 6Y6s in series. Thing I like about using valves is that they're a wee bit more bomb-proof than silicon in that position...

 
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Re: Homebrew HT Bench power supply.

Post by GlowingAnode » Wed Aug 19, 2015 8:17 am

Indeed as Catho' says valves are a little more forgiving than silicon.
I did consider using 6080s but they are heater hungry and have a lower combined anode dissipation and anode voltage.
I'll post some diagrams later for you Andy.
Cheers Rob.

 
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Re: Homebrew HT Bench power supply.

Post by EDDINNING » Wed Aug 19, 2015 8:17 pm

Hi Rob, I've built versions of the Farnell unit using 807's and they work fine, even though the regulation is down to Ge transistors. It also has current limiting which is useful. I couldn't see if yours offered this feature ?

That was a good use of a transformer, these are difficult to come by for this type of PSU unless you wind your own, which fortunately I do, but they are complex beasts with many taps. I see you also had some suitable HV switches. Modern types, even break before makes will not handle the voltages and currents in these PSU's.

Ed

 
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Re: Homebrew HT Bench power supply.

Post by GlowingAnode » Wed Aug 19, 2015 8:45 pm

It's a very simple design, pretty conventional, no current limiting only fuses.
The switches are high quality items, silver contacts, 36(?) way with a 12 position cam fitted, giving 3 contact gaps between ways.
I attached a general arrangement for interest, drawn from memory.
Andy, these Tek transformers make super power supplies as they have several ht and lt windings and seem to be well rated, around 750 VA I think. You could (those of a nervous disposition look away now) always remove the p/s section from your spare 545 and you have a very useful ready made bench supply.

Cheers, Rob.
Attachments
PSU(1).png
PSU(1).png (114.13 KiB) Viewed 2177 times

 
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Re: Homebrew HT Bench power supply.

Post by GlowingAnode » Wed Aug 19, 2015 9:33 pm


 
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Re: Homebrew HT Bench power supply.

Post by GlowingAnode » Wed Aug 19, 2015 9:42 pm

GlowingAnode wrote: You could (those of a nervous disposition look away now) always remove the p/s section from your spare 545 and you have a very useful ready made bench supply.

Cheers, Rob.


See attached, power supply chassis circled in red.
Original photo courtesy of radiomuseum.org

Rob.
Attachments
545a_156550.jpg
545a_156550.jpg (68.23 KiB) Viewed 2164 times

 
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Re: Homebrew HT Bench power supply.

Post by Dr Wobble » Sun Aug 23, 2015 4:39 pm

Thanks for the link Rob, interesting stuff. I have most of the bits inc several 807's, big case and big caps, but don't want to canabalise a 545 for it's transformer, not yet anyway. I have a couple of huge LT transformer's something like 12 - 20v 10A I could boost up using a CW tripler type circuit, but it's not straight forward as using a tfmr with HT secs.

A project for the future as have quite a few jobs need doing.

Andy.

 
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Re: Homebrew HT Bench power supply.

Post by EDDINNING » Sun Aug 23, 2015 7:26 pm

Hi Andy, if you have a big enough transformer you could always strip it and re-use the lams and bobbin to make the HT transformer.
Be careful though as this transformer can supply 400v @200mA, enough for a serious death !!

Ed

 
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Re: Homebrew HT Bench power supply.

Post by GlowingAnode » Sun Aug 23, 2015 10:49 pm

I always salvage any old control transformers I find in the metal bin.
Any EI core transformer 250 VA plus is worth saving for re-winding as these have enough space on the former for a decent ht winding, and are low enough turns per volt not to be tedious.
I seem to have an ever growing collection beneath my feet.

Cheers, Rob.


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