[Drakelist] AC-3 (and AC-4) CheckingPaul GerhardtWed, 02 Nov 2011 08:06:43 -0700 Here are some reference readings for an original AC-3 that is workingwith full power and reasonable audio reports. It is out of specthough and running warm. Note: Recommended Max Ripple is 2VAC on HV 1VAC on 250V line and .5VAC on Biasfrom http://www.wb4hfn.com/DRAKE/DrakeArticles/TechTips/PowerSupplyTroubleshooting.htm
Brown 120VACBlack 0VRed 13.68VACYellow 268 VDC 4.9VACOrange 714 VDC 421Vac Jumping to 3hundred somethingWhite 0VGreen 61VDC 0VAC Temps measured with AC3 upside down with bottom off sitting on pieceof carpet on for a couple of hours. This is interesting because youcan 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 styrofomesheet 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 30C3rd one in line 27CNext to Bias Pot 27Cin Corner 25CElectrolytic with leads 29 CPower Resistor 44 C I could not tell any difference by touch on the top of the caps (DONOT TOUCH ANYTHING under the cover until you are sure the caps aredischarged ALL the way).With the temp probe the warmest cap is the one with the high ripple sothat is maybe a reasonable way to test. The AC-4 that was giving the 'Bad' Audio reports was dropping the OA2tube 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 TOOHot. Both supplies are overdue for new caps and I have ordered one new P/SKit 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 thatI am still working on but had been testing it with the AC-4 that wasworking. Due to $ I think I will put the new upgrade on the AC-4 and move theUnder 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. Costis currently $2-3.5 each and so if you change the out of spec ones andmaybe new diodes if you want and maybe the power resistor if it is outof spec from running hot for too long. The upgrade board is probablyeasier if you need to change more than one or two items. Received the 'Heathkit Shop' board and installed it. Here are the new readings and a couple of things to consider. The OA2 tube NO Longer Goes Dark and the Audio reports are back to good! PTT line closed Voltages are 720VDC with .6VAC 267VDC with .4VAC -60VDC with .0VAC So if your OA2 is dropping out you are losing your 250V filter it seems on an AC-3 or AC-4 The Heathkit Shop kit was a simple way to change everything at once and as I already had put 'under chassis' B+ caps in the AC-4 and then the 250V filter failed as well I went ahead and opted for the Heathkit Shop board. I ordered the printed instructions and the wire kit too for an extra $10 and was a bit disappointed because the wire kit is cut for installing the board on only one side of the transformer but one HAS to put it on the side where the nuts are and not all the transformers had the screws pointing the same way. There are pretty well 'fixed' in place with whatever they dip the transformers in. Another foot or so of each color wire would have enabled me to install it the way Mike intended with the use of the terminal strip, instead I had to splice some pieces together to make it work and I still needed ten inches of a stripped out CAT 5 wire to com pleat the project so I would have been better off spending the $10 on wire myself. Anyway it is together and working and will probably work for another $50 years. If you are contemplating one of Mike's boards I would highly recommend it but I would check your transformer and see if the nuts are toward the '3 cap' side of the AC-4 or towards the '2 Cap' side of the AC-4. Mike designed the wire kit for the nuts facing the '3-cap' and larger side of the chassis. -- Paul Gerhardt K3PG http://pgerhardt.blogspot.com QRP ARCI 6674 FP 274 "You must do this work with love or you fail." -- John Muir, from How to Keep Your Volkswagen Alive _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
