When considering a VTVM one should look at one thing in particular, tube replacement. The Senior Voltohmyst uses a 6AL5 and a 12AU7 . Finding tubes is not a problem, but for reasonable accuracy the right tube is.
According to the manual for the Voltohmyst, the tubes must be thoroughly aged. For example, to age the 12AU7 the grids and cathodes are connected to B- and the heathers be operated at 6.3 volts for approximately 12 hours before installation. The tube can be installed then left turned on for about 36 hours then the instrument must be re-calibrated. If the second method does not provide proper results, the first method should be followed. The 6AL5 can just be aged by leaving it on for about 36 hours, but then re-calibration must follow. While neither of these methods are particularly difficult, how many of us have standard sources to calibrate our meters? It seems to me a good modern Fluke meter might be the best choice. They are not easily destroyed nor go out of calibration easy. Some are sensitive to high RF fields which blow the input protector. I have had that trouble with a Fluke 77. Most, if not all provide a high impedance input and are rugged. Granted using them to tuned for peak resonance is difficult, Sears sells a dual digital/analog meter with high impedance. They are not terribly expensive and can provide both digital and analog readings. 73 Jim de W5JO ----- Original Message ----- From: "Merz Donald S" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" <[email protected]> Sent: Tuesday, August 24, 2004 9:21 AM Subject: RE: [AMRadio] Test Equipment Recommendation > Really? Is this the best recommendation that we can come up with? Every one of these that I see is awfully beat up after 30-50 years. And these were not especially high quality units to begin with. > > On the other hand, I don't know what else to recommend. I am using an old Radio Shack Micronta VTVM, probably from 1970. I've had a Simpson 303 (these do not age well--to be avoided) and the RCA VoltOhmyst in several different flavors, plus several other brands. The Micronta has delivered the most reliable, accurate service of any of them. But I can't really recommend that because nobody could ever find one. > > Given the advanced age of the VTVMs that survive today, this actually is a harder question than it first seems. > > 73, Don Merz, N3RHT > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Edward B Richards > Sent: Monday, August 23, 2004 11:27 PM > To: [EMAIL PROTECTED]; [email protected] > Subject: Re: [AMRadio] Test Equipment Recommendation > > > Bill; > > Go to that auction place and buy a Heathkit VTVM. There are usually a lot > of them listed. All are 11 megohm input impedance. Then buy an RF probe. > The later VTVM's have a phone jack input and so do most RF probes. Also > known a demodulator or scope demodulator. Good luck > > 73, Ed Richards K6UUZ > > > On Mon, 23 Aug 2004 19:30:22 -0600 (GMT-06:00) Bill Pancake > <[EMAIL PROTECTED]> writes: > > Would appreciate a recommendation as to make and model of a VTVM that > > will come with an rf probe that is suitable for using when working > > on boatanchor gear. I just need an idea of what to look for. > > Thanks, Bill, [EMAIL PROTECTED] > > > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:[email protected] > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > > 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.(B) > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > >
