I think you guys are getting carried away with technicalities. We are not space laboratories, we are amateurs. Look at your license. Nearly all VTVM's use a 12AU7 and a 6AL5. They are available in abundance. I have about 50 of each. Any good used tube will be aged. Even if recalibration is required we are talking about removing 2 screws and adjusting 3 pots. Not an all day job. Re calibration, Heathkit used a fresh zink-carbon battery for a terminal voltage of 1.55 volts. I use a fresh alkaline battery with a terminal voltage of 1.62 volts. It works for me. For ACV if you don't have another meter or a friend that does, wait for early morning when the electrical grid is lightly loaded and calibrate your ACV for 122 VAC. You will be in the 5% accuracy of the VTVM.
73, Ed Richards K6UUZ On Tue, 24 Aug 2004 11:43:39 -0500 "Jim Wilhite" <[EMAIL PROTECTED]> writes: > 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" <amradio@mailman.qth.net> > 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]; amradio@mailman.qth.net > > 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:AMRadio@mailman.qth.net > > > > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > > > 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:AMRadio@mailman.qth.net > > > > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net >
