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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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5th Nov 2019, 6:37 pm | #1 |
Hexode
Join Date: Nov 2011
Location: Chippenham, Wiltshire, UK.
Posts: 319
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Roband Electronics M34 PSU
A long shot - there's nothing on the Web although Roband is still going after 60 years.
I purchased a very grubby rack panel at the recent VMARS auction and discovered inside it a Roband M34 stabilised PSU. Hefty Partridge transformer, block paper capacitors, GZ34 rectifier, EL34 series regulator plus a couple of 12AX7s and an 85A2. Does anyone have a circuit diagram to share or more accurate details about the outputs? The two preset pots have only a limited effect on the output voltage, varying it from around 200 to 220 volts. The unstabilised voltage at the smoothing capacitors is a whopping 540 volts, although that measurement was taken under no-load conditions. Photos can be provided if that will help. Peter G3PIJ |
5th Nov 2019, 7:54 pm | #2 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
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Re: Roband Electronics M34 PSU
If no circuit available I would check the reses and caps carefully around the control circuitry.You may well find high reses have gone even higher.
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G8JET BVWS Archivist and Member V.M.A.R.S |
6th Nov 2019, 3:36 pm | #3 |
Hexode
Join Date: Nov 2011
Location: Chippenham, Wiltshire, UK.
Posts: 319
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Re: Roband Electronics M34 PSU
The PSU works OK so none of the passive components can be that far out. My main question is about the specification: 200-210 VDC out - but at what maximum current?
The EL34 is used as a series-pass element and its maximum anode current is given as 91 mA. From this, is it OK to assume that the PSU is rated at a nominal 100 mA? The EL34 maximum anode dissipation is 25 W: it can drop 250 V at 100 mA before exceeding this dissipation, which allows the unregulated voltage to be 220 + 250 = 450 V. I have measured 540 V unregulated but that was at zero load. . . . . . perhaps I am answering my own question here! It would still be nice to have sight of a circuit diagram to save tracing it out. Then I can replace the EL34 with an S11E12 and sell the EL34 to the audio brigade. Also - why does it have 2 x 12AX7 instead of the much simpler EF91 or similar? None of the standard circuits that I have seen uses a pair of double triodes. Peter G3PIJ |
7th Nov 2019, 11:56 am | #4 | |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Roband Electronics M34 PSU
Quote:
Al. |
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