Valve lab power supply - APT Model 501I have seen on another forum a schematic o

[djrm]

I bought this at a local radio rally a few weeks ago. Inside there is a large mains transformer, selenium rectifiers, a gas voltage reference, two EF91s and three 807 valves. The voltage adjustment pot had its wiper broken and a new pot restored operation. The mains caps seem ok (ooerr, hope for the best) it has had some repairs including some cap replacements in the past. The meter has been replaced with a modern (ish) kind.

I have seen on another forum a schematic for a similar model which has been very useful but its not quite like the one I have in some details. Any more information anybody?
Kind regards, David.

   

[Diabolical Artificer]

Old bench PSU's are tricky to find manual's and schematics for, I have a KSM SCT 500 3 500v 3A bench PSU with no info on it at all but managed to fix it when it developed a fault. It's very complex, yours though is hopefully simpler, it should be pretty straight forward David, a DC supply from the tfmr and smoothing caps into the the 807's probably connected in parallel as the series pass element, the gas valve as the voltage reference and the two EF91's as error amp and 807 "driver.

Is it working ok or does it have a fault? You could try giving Telford a ring, their site shows a few APT manual's - http://www.telford-electronics.co.uk/manual.php?alpha=a but not yours. Studying a few similar bench PSU's might help you draw out a schematic, see - http://www.pmillett.com/HV_bench_supply.htm & http://diyaudioprojects.com/mirror/membe.../reg1.html for more info.

Andy.

[Ed_Dinning]

Hi David, it looks quite a simple unit, without the complication of current limiting so should be quite robust

Ed

[djrm]

Thanks for the schematic links Andy, the first will surely be very similar to what I have. The manual for the similar model is here: http://www.electrojumble.org.uk/DATA_2/APT_504.pdf but it is for a more complicated version but very simiar in many ways. Ed, the selenium rectifiers will surely provide a degree of protection - lol.

[Ed_Dinning]

Hi David, yes a nasal warning of failure.
It always seemed short sighted that these pieces of kit, usually quite expensive were never sufficiently fused. Always worth adding additional fuses in the feeds to HT rectifiers etc

Ed