HP 721A Power Supply PP-3514/U

© Brooke Clarke 2011

I first saw this supply being used at the HP facility in the Stanford Industrial part just off Page Mill Rd. and really liked it since it was a small DC supply with variable output voltage and it has switch selectable current limiting, just the thing for developing solid state circuits.

Later the _____ series power supplies came out with dark gray plastic enclosures.  They have variable current limits (CVCC operation), but the plastic cases are not as nice as the drawn metal cases.

The package had a rattle and when the 721 was opened up the main electrolytic capacitor bakalite mounting wafer and broken so only wires were holding it in place.
A power on check (making sure the cap was not touching anythng) showed normal operation.

Used J-B Weld expoxy to hold it in place.

The photo at the top of this page shows the voltage at 25 when the pot is turned fully clockwise and this spec is 30 Volts, so out of spec.
There are a couple of pots on the bottom PCB, one for setting Vmax and the other for setting Imax and they are marked so you really don't need the manual to do it.
Photo after setting Vmax to 31 V and with Imax set to 230 ma (spec is 225 ma).

The PP-3514/U manuals are:
TM 11-6625-617-12 Operation
TM 11-6625-617-45 Maint

HP Journal May 1958, Vol. 9 No. 9: A Current-limiting Regulated Power Supply for Transistor Work - 

[an error occurred while processing this directive] page created Nov 18 2011.