[R-390] HP410B rectifier tubes

[Barry]

Oops.  Make that 300mA heater current; not 500uA.  I was looking at the
wrong part of the specification.

Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq at knology.net>
To: <r-390 at mailman.qth.net>
Sent: Sunday, March 26, 2006 4:02 PM
Subject: Re: [R-390] HP410B rectifier tubes


> I had a chance to do a little more testing.  It seems the diode is only
> pulling about 11 microamps (depending on the accuracy of my meter) which
is
> not correct (should be 500 microamps).  I'm seeing approximately 6.3VAC at
> the socket and the tube itself has slight resistance across its filament
so
> I must have something else going on.  Looks like another "project".
>
> Barry - N4BUQ
>
> ----- Original Message -----
> From: <n4buq at knology.net>
> To: <r-390 at mailman.qth.net>
> Sent: Tuesday, March 21, 2006 8:06 AM
> Subject: [R-390] HP410B rectifier tubes
>
>
> > Many of you own the HP410B VTVM and use them on your R39* series radios.
> I
> > have one and some time ago, I noticed the AC probe stopped working.
> > Normally, after an hour or so, the probe will become warm due to the
> > rectifier tube's filament and mine had stopped warming up.
> >
> > Figuring the diode in the AC probe had died, I recently started looking
> for
> > a replacement diode.  As many of you also know, these tubes are becoming
> > quite expensive.  Knowing this, I decided to check everything out as the
> > tube itself may not really be the problem.
> >
> > Some of the meters use a 2-01C diode, some use an EA53, and others may
> have
> > a probe where either type can be used (there are supposedly slight
> physical
> > differences between the two tubes making them not completely
> > interchangeable).  Mine has an EA53 and I checked the specs for it.  I
> > noticed that the 2-01C uses a 5.0VAC filament while the EA53 runs on
> > 6.3VAC.  Checking in my manual, it states to set the filament voltage to
> > 5.0VAC and that was what I did when I went through it a few years ago.
> >
> > A little reading on the internet reveals that if your meter uses an
EA53,
> > you should set the heater voltage to 6.3VAC, not 5.0VAC and some manuals
> > may even make mention of this (mine does not).
> >
> > There is a variable resistor used with a ballast tube to set the heater
> > voltage.  I set the heater voltage at the probe to 6.3VAC and reinserted
> > the EA53.  I let it warm up for about an hour and, sure enough, the
probe
> > began to warm up again.  It is again working in the AC modes; however,
it
> > reads quite low (about 30VAC where it should be seeing 120VAC).  I think
> > this is just a calibration thing and I can fix that.
> >
> > I just thought I'd pass this along in case others may have experienced
> non-
> > working AC probes and not realizing it may just be an incorrect heater
> > voltage setting.  Check the diode in your probe first, though!
> >
> > Barry - N4BUQ
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