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Old 8th May 2011, 11:24 pm   #1
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Default GPO LST4 power supply 86B

I've just managed to acquire something I've dreamt of owning since I first saw it when I was a LST4 loudspeaking telephone. It appears to be in great condition, with a proper block that doesn't appear to have been used as the break-out for the incoming cable has not been broken.

However, I'm struggling to find a suitable power supply for the LST4. The GPO 50v dc power supply number 86B is nowhere in evidence on the interweb, nor on Ebay where I sourced the LST4 (which in fact turns out to be the very last model produced, the 4265, which was designed to deliver DTMF tones for proprietary PABXs - although I thought I was buying an earlier LST4D with rotary dial).

If anyone has any ideas on where to get an 86B PSU, or has one knocking around they'd like to get rid of to a good home, please let me know. Alternatively, if someone can suggest a suitable modern PSU that would drive the LST4, I'd be grateful for any assistance. There's no indication on what amperage the 86B 50v dc PSU delivered...again, any thoughts from people who understand electrical stuff would be very much appreciated.

It certainly demonstrates how electronics have developed over the past 40 years since we can now drive pretty much all electronic devices from just 9V!
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Old 9th May 2011, 12:04 am   #2
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Default Re: GPO LST4 power supply 86B

Hi Simon

I come across the odd 50 volt (1 amp) "Wall wart" at work. Would one of those be suitable?
You'll have to connect it your self but it's a start.
Drop me your contact details by Private Message (click on my name above the little monkey) and I'll let you know if I find one.
"Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."
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Old 9th May 2011, 4:11 pm   #3
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Default Re: GPO LST4 power supply 86B

Just in case you don't already know, the supply (once you have one, that is) goes between the orange (+ve) and blue (-ve) wires of the cable.
Mending is better than Ending (cf Brave New World by Aldous Huxley)
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Old 9th May 2011, 7:26 pm   #4
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Default Re: GPO LST4 power supply 86B

Many older video recorders have a mains transformer with a 40 Volt AC winding to power the VFD; if you can obtain a transformer from a scrap VCR all you would need to do is rectify and smooth the output and that should suffice.

I don't think that the 50 Volts is critical as long as it's close, and the original GPO power supplies only used a basic smoothing circuit with no fancy regulation.

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