Confirmed that you had received the heat sink insulative items that I had sent you for the motor driver cktry, . some of the larger insulators……...but not the silicone units……should also be compatible with your TO-3 plastic casings or just custom cut from the mylar sheeting.
I see that you are now in a quandary with its PS. Following down on the comments on the PS troubleshooting I didn’t ever see reference to the voltage rating of your filter cap. Also its not at all uncommon to see Sprague reforming their units…..a pristine unit with good seal integrity and with an inert gas fill can last one long time. Also you can check for code date of manufacture on the unit you have, if curious, I see one unit at hand marked as 7945 then followed by 8212 which would translate to a manuf date of the 45th week of 1979 and then a reform at the 12th week of 1982.
I experience a minimal ESR problem on electrolytics at LINE FREQ operation in linear supplies but is of utmost importance in switch mode supplies where they’re getting hammered by those high current square waves at ten’s to 100’s of khz rates. One quick spot check I do on equipment is to check the compression indentations
on the end cap for any bulging, a delayed forewarning of the unit having pressure buildup internally. Also a
simultaneous low tech /high info touching of a fingertip to that end cap to make a temperature check. High
ESR and hi temp go hand in hand , so time to cull out those units before rupture of that expansion crimp or the worst case…..explosion of a unit and dispersion of all its confetti foil and electrolyte (IF any is left) into the internal electronics.<p>Relevant to the transformers rating, which I am uncertain what it was actually rated at, I believe that and the filtering are your last hang-ups as Ron cued you in on the current sharing and its parts parameters in the reg circuitry. If you were in loss of the odd value of pot just put a smaller fixed res in series to get on up into the higher voltage range required and
thereby leaving the pots adjustment range deficient in the lowest voltage area which is typically of no interest to U.
On older Mil/Aero/Ind surplus transformers I would use the same technique that you finally used in dumping the raw filtered DC voltage from the Xformer/FWB rect/Filter(s) into a dummy load. Initially measuring the DC voltage unloaded I would expect it to drop 10% when it was loaded down to the specs on the transformers sec winding.
Lately I’ve seen transformers that drop down up to 20%. The voltage you experienced is shy of your desired amount considering the pass element losses in your regulatorcircuitry. If I were in the same situation and all of the transformers I have wound/modified….but primaries are NO fun……If this was an open exposed core design I would surgically cut across the heavy paper/fishpaper outer insulative covering of the bobbin and expose the sec winding which I would expect to be ~#18-20 ga (*) wire for those current specs and see if there was clearance in the window to accommodate one more winding layer which should just bring you up to that required extra voltage/power you need.Premeasuring your wire length and interleaving in the winding without the necc of core breakdown. I feel the core area mass would be tolerant of the few extra watts that you were shy of.Typically your application is not for continuous max pwr use. On the ripple I usually bring the primary voltage up on a Variac and just watch the output on a scope at the dummy load and watch to see if the filtering was adequate at that loading by seeing the percentage of that quasi-sawtooth present. If no scope, use the AC scale of a meter, but some cheaper meters act squirrelly with a DC component also present , so just read thru the isolation provided by a 1(+) ufd paper/poly/mylar of adequate voltage rating.
If you find your filtering to be deficient I see a prime 18,000 @ 75VDC cap with a ’97 code date in my bench... gratis if U need.
Another easier fix, if U happen to have the transformer on hand, is to take a unit with a 6.3 VAC secondary with a current rating of the same or greater current than you need and place its secondary….. series aiding…. with your main transformers secondary.
Addenda (*): Enamel/Formvar wire..... available from an electrical motor rebuild/rewind shop.<p>73's de Edd
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<p>[ March 19, 2003: Message edited by: Edd Whatley ]</p>