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Old 19th Aug 2004, 1:18 pm   #1
Rod H
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Default PSU Transformer for R1155 Project

I'm getting fairly close to completing a major rebuild of an R1155 Receiver and now turning my thoughts to building an internal or external power supply unit.

My assumption is that 250-0-250v at 100mA and 6.3v at 3A should suffice (I'll probably use silicon rectifiers so no real need for a tertiary winding).

If anyone is able to supply a second hand item of similar spec I'd be grateful to hear, as the price from the suppliers of new items looks rather steep.

Rod H
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Old 19th Aug 2004, 3:12 pm   #2
Chris_C
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Default Re: PSU Transformer for R1155 Project

Hi Rod

If you are going to use silicon rectifiers, using one of the small bridge types would mean you wouldn't need a centre tapped secondary.
Maplin do one that is 240V @ 100mA but is only 1.5 amps on the 6.3 volts winding . It's about 13 quid.
This way might make it easier to come up with a suitable type at reasonable cost.
Also if making an external psu, you might think about a small amp and loudspeaker in the same box.

Cheers
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Old 19th Aug 2004, 6:05 pm   #3
paulsherwin
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Default Re: PSU Transformer for R1155 Project

I have a few hefty ex-equipment transformers in the garage. I'll have a look for a likely candidate if you like. They're mostly unmarked, but you should be able to derive the correct HT from any sensible value with suitable resistors. You'll have to use a bit of trial and error to work out which winding is which, and the current ratings will be a bit of a guess.

The trouble is, these things are heavy and will be expensive to post. I don't suppose you live anywhere near Oxford?

[added later] I've had a quick look and found a reasonable candidate. It looks late 50s/60s and is in good cosmetic condition. Unfortunately I don't know the current ratings - you'll have to put it on load and see if it runs hot! You can have it for the price of the P&P, which will be £5.

Best regards, Paul

Last edited by Station X; 27th Dec 2004 at 9:19 pm. Reason: Import
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Old 20th Aug 2004, 1:19 pm   #4
RobinBirch
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Default Re: PSU Transformer for R1155 Project

Sorry to come to this so late. From memory, you will need at least 70mA for the HT which is 200V. The LT is 6.3V but is ideally DC, the set is not built for AC heaters and so you will get a bit of 50Hz noise is you go down this path.

I built myself a stabilised PSU (EL34 supplied with 300V I think) and a clean (ish) DC supply giving at least 3A. 4A if you are using the DF circuits.

The HT is NOT clamped to ground. This floats up and down with the AGC.

Cheers

Robin
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Old 20th Aug 2004, 8:08 pm   #5
Rod H
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Default Re: PSU Transformer for R1155 Project

Paul

Many thanks for looking the item out. For the cost of a fiver I think I'll take you up on the offer, and take the chance that on closer inspection it might turn out to be suitable. If not, I'm sure it will come in useful one day for something else.

I live in Flitwick, Beds and although not that far from Oxford, on balance I think posting it would be simpler all round.

I'll send you a PM shortly

Kind regards

Rod
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Old 20th Aug 2004, 8:20 pm   #6
Rod H
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Default Re: PSU Transformer for R1155 Project

Robin

Thanks for the tip as regards the LT supply, which is perhaps no surprise as the return leg for each valve heater is via the chassis (rather than one half of a twisted pair). I did begin to wonder if hum could be a problem if using AC power, but interestingly the Radio Constructor series of modifications in the late 50s makes no mention of this, and doesn't propose any rewiring despite the modification of the time powering the heaters with AC. From this I tended to presume that theory perhaps didn't translate into practice when it came down to it.

However, as doubt has now been cast, I think I'll opt for 6v DC just to be on the safe side!

Rod
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