[GreenKeys] 120VDC power supply noise?

[Eugene Hertz]

Hello, Harvey! Thanks a bunch for some excellent troubleshooting/analysis ideas. I will try some of them as soon as possible. The only other few things I can tell you are a) output is rated at 80ma b) I disconnected both secondaries (one to the rectifier and one to the capacitor) and STILL got that infernal hum! 

Considering I will be using this with teletype gear (28's) and from what I understand voltage regulation is not that critical, couldnt I merely substitute the transformer for any garden variety one? (hopefully one that doesnt hum!) Like, perhaps, the kind in an ST6 or similar?  Or course, locating such a beast might not be trivial.

Thanks again, I will do more studying tonight
Eugene


-----Original Message-----
From: KC0NNC at aol.com [mailto:KC0NNC at aol.com]
Sent: Sunday, October 9, 2005 09:37 PM
To: ehertz at tcaf.org, WA5CAB at cs.com, greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] 120VDC power supply noise?

If you have a variac, try placing the supply on the variac, and see how stable the output voltage is as you run the ac input voltage up and down, If this is a sola unit, then you should see a very small change in the DC output as you run the ac mains from 100 to 140 vac input.

also, you could place a 1 ohm resistor in the two transformer output leads before the ac capacitor and the bridge rectifier, and all the components that follows, and then place the ac dvm, across each resistor, and see what the voltage drop is across each resistor, this will tell you if the following circuitry is pulling excessive current, and what type of current. I would also try and estimate the supply output voltage and current capability.


Lets say it is rated at 110 vdc out at 1 amp. Then you could use a 100 watt incandescent light bulb for a load, and see how the supply behaves, while running the variac up and down. also try smaller bulbs to see how it regulates under less loading. etc, etc. I would consider leaving some kind of resistance into the bridge for surge protection. 1 to 10 ohms carbon 2 watt generally works well, depends on the required output current of the supply

sort of fun qualifying power supplies in this fashion. I once had a 4 kV @ 1 amp. DC supply for an Eimac tube I needed to check out, and series the appropriate number of 1 amp. 120 vac bulbs (about 40 of them)[cheap enough at $0.25 ea.} set them on a plywood board, and ran it for an hour or so... confirming the supply was ok, then went on to find the bad tube socket under the 4cx3000 Eimac tube.

At 60 years of age, I can attest that I was, and continue to be, quite careful while working with these voltages and currents.

73's
Harvey E. Smith, KC0NNC
2020 Baculite Mesa Road
Pueblo, CO., 81001-2456

719 406 9735, 719 671 2671, 719 546 1418

zzzz/ryry