Don, I never tried this idea but here is what I would do. I'd try to simulate a 1.5v battery where it was a floating supply with low noise, and low source impedance (Rs). I would take an isolated DC-DC converter, say 12 volts input to 5 volts output at 100ma. Then I'd use a 3 terminal adjustable regulator like a LM-317 (or any of the many similar parts). This regulator works down to 1.25 volts, and it is simple to adjust to 1.5v with two resistors. So now you have a floating 1.5 v source that is clean, and has low source impedance. To get the 12 volts I'd use a 1/2 wave voltage doubler off the 6.3v filament circuit and another LM-317 to provide 12v to the DC to DC converter.
There might be easier ways for sure, but emulating a floating dry cell, if done properly will work. Some ohm-meters may pull 100 ma or more on the R X 1 range so you need to maintain 1.5 volts at whatever the shorted test lead current is when on the R X 1 range. Using a fresh battery once a year might be easier! :-) Regards, Jim ----- Original Message ---- From: Merz Donald S <[EMAIL PROTECTED]> To: Discussion of AM Radio <amradio@mailman.qth.net>; 'Glowbugs (E-mail) <[EMAIL PROTECTED]> Sent: Thursday, July 20, 2006 11:26:52 AM Subject: [AMRadio] VTVM Battery Eliminator Going through these old magazines, one idea that pops up a few times is replacing the OHMS battery in old VTVMs with some sort of regulated 1.5V derived from the VTVM's AC supply. The circuit designers seem to be a bit at odds over the best way to accomplish this. Has anyone does this with a circuit that they are happy with? I'd like to do this to one or more of my VTVMs but I don't want to experiment with it--I want an optimal circuit that will be reliable. Anybody got one? 73, Don Merz, N3RHT The information contained in this e-mail may be confidential and is intended solely for the use of the named addressee. Access, copying or re-use of the e-mail or any information contained therein by any other person is not authorized. If you are not the intended recipient please notify us immediately by returning the e-mail to the originator.(17b) ______________________________________________________________ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
