Here are some reference readings for an original AC-3 that is working with full power and reasonable audio reports. It is out of spec though and running warm.
Note: Recommended Max Ripple is 2VAC on HV 1VAC on 250V line and .5VAC on Bias from http://www.wb4hfn.com/DRAKE/DrakeArticles/TechTips/PowerSupplyTroubleshooting.htm Brown 120VAC Black 0V Red 13.68VAC Yellow 268 VDC 4.9VAC Orange 714 VDC 421Vac Jumping to 3hundred something White 0V Green 61VDC 0VAC Temps measured with AC3 upside down with bottom off sitting on piece of carpet on for a couple of hours. This is interesting because you can estimate this to some degree. Side of Transformer 57 C (Very warm to hand uncomfortable after 20 sec or so) Caps - Measured at top of cap with unit upside down with styrofome sheet underneath and probe between styrofoam and top of cap Three large caps L to Right (upside down from bottom) HV can with orange lead 35 C (the one with high ripple) HV can 30C 3rd one in line 27C Next to Bias Pot 27C in Corner 25C Electrolytic with leads 29 C Power Resistor 44 C I could not tell any difference by touch on the top of the caps (DO NOT TOUCH ANYTHING under the cover until you are sure the caps are discharged ALL the way). With the temp probe the warmest cap is the one with the high ripple so that is maybe a reasonable way to test. The AC-4 that was giving the 'Bad' Audio reports was dropping the OA2 tube to 'dark' The AC-3 the OA2 would just dim a bit and audio reports were 'better' but the Ripple is out of spec on the HV by a lot and it is running TOO Hot. Both supplies are overdue for new caps and I have ordered one new P/S Kit from Heathkit Shop. The AC-4 had been upgraded a couple of years ago with 'under chassis' HV Caps but the 250V section has now failed it seems. The AC-3 had not been tested by me. It was acquired with a TR-4 that I am still working on but had been testing it with the AC-4 that was working. Due to $ I think I will put the new upgrade on the AC-4 and move the Under Chassis HV caps to the AC-3 and continue to use it for a while. There is room for new under chassis caps if you want to do it. Cost is currently $2-3.5 each and so if you change the out of spec ones and maybe new diodes if you want and maybe the power resistor if it is out of spec from running hot for too long. The upgrade board is probably easier if you need to change more than one or two items. Side of tran _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
