Hi Perry, While I agree with everything else you say, you CAN have too much filter capacitance. At least where dc rectifier / filter (smoothing) circuits are concerned. Increasing C causes increased ripple current and inrush current and can overstress rectifiers and transformers. Not actually a problem in most cases, but if the rectifier or transformer is already marginal, blindly slapping in a much (>2x) larger capacitor can cause troubles.
Robert G8RPI. ________________________________ From: Perry Sandeen <sandee...@yahoo.com> To: "time-nuts@febo.com" <time-nuts@febo.com> Sent: Friday, 14 June 2013, 5:48 Subject: [time-nuts] HP and other equipment failure All, There has been an on and off discussion of equipment failure so I’d thought I’d add my experience. First I’ve been repairing HP equipment since 1976 before many of you were born. I now have over 16 pieces of HP test equipment and several units now need repair. In my experience, the vast amount of failures are electrolytic caps with some aggravated by heat. Someone floated the notion of not repairing HP equipment but cannibalizing it for parts. Please bear with me on my long story. After WWII there were all sorts of surplus stores selling everything in the mid-fifties. I even remember an add in popular Mechanics magazine for a Norden bombsite for $29.95. Much of my allowance was spent on mysterious wonders like a IFF receiver. Hams reveled in B-29 prop pitch motors for rotating beam antennas. Since it was 28 volt stuff it was far, far cheaper than commercial equivalents. Then it all gradually disappeared. Now people want $75 or more for a cruddy ARC-5 receiver. Now this is how it applies to us today. If one peruses the Ebay adds for HP test equipment one frequently sees a statement like *removed from a place that went out of business* or something similar. True, the equipment we are buying is 20 years old or older. But it is going away never to return. I saw an old Ebay invoice from 12 years ago where I won a working HP 3586B for $50. The shipping cost me more! Now a non-functional unit sells for $400. These prices are only going to continue to rise as the supply continues to diminish. But this equipment is repairable unlike the questionable test equipment from China. Doing preventative maintenance on this equipment is not optional if you want it to continue working. All electrolytic caps should be replaced, except for tantalums. That will be more on a case by case business. This is equipment you can repair. This is not very true for the newer stuff. On the HP 3586B for example, there are a dozen or so of TVA atoms. When I do mine I expect it will then lock below 500 KHz as it is specified. The HP 5370B needs far more cooling than provided. I have even given thought to adding additional resistances to the pass transistor collectors on the outside by the heat sink. I found on my two that the mother board was scorched from overheating by rectifier diodes. This will have to wait until after we have moved. I will also add EFC to the 10811 oscillator. (Why that feature was omitted can be answered by Ric). There are two long standing truths about electronic equipment. One you can’t have too much filter capacitance. Two, you can’t cool too much. (Please spare me the liquid nitrogen or submarine battery comments.) Regards, Perrier ________________________________ _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
