[AMRadio] Test Equipment Recommendation


Jim Wilhite w5jo at brightok.net
Tue Aug 24 21:15:36 EDT 2004


Gee Ed, didn't mean to flip your switch.  Grid voltage here is 125 AC
loaded, I have seen carbon zinc batteries @ 1.15 volts out of the package.

None of this is really critical, but any amateur should use good engineering
practice, or did I misread some rules?

73  Jim
de W5JO
----- Original Message ----- 
From: "Edward B Richards" <zuu6k at juno.com>
To: <amradio at mailman.qth.net>
Cc: <amradio at mailman.qth.net>
Sent: Tuesday, August 24, 2004 2:53 PM
Subject: Re: [AMRadio] Test Equipment Recommendation


> 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" <w5jo at brightok.net>
> 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" <merz.ds at mellon.com>
> > To: "Discussion of AM Radio" <amradio at 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: amradio-bounces at mailman.qth.net
> > > [mailto:amradio-bounces at mailman.qth.net]On Behalf Of Edward B
> > Richards
> > > Sent: Monday, August 23, 2004 11:27 PM
> > > To: bpancake at mindspring.com; amradio at 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
> > > <bpancake at mindspring.com> 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, ab0zz at arrl.net
> > > >
> > > >
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