[Heath] Heath Digest, Vol 97, Issue 9

[Al Skierkiewicz]

Richard,
Bad capacitors are often the cause of problems in older equipment.  While
oscillating circuitry can cause this issue, a shorted DC blocking cap like
the 2 mfd cap in the plate lead of the final stage amplifier.  However,
knowing the age of this device, the first thing I would to do is replace the
filter cap which is a dual 20 mfd/150 volt electrolytic.  If you have a
normal multimeter, set the meter to AC and put the probe across first one
section to ground and then the other.  If you read 20 volts or more across
either or both caps, they are not producing a clean DC voltage.  Does the
meter go full scale while it is warming up or does it go full scale
immediately upon turning the meter on?  Does the meter go full scale on all
ranges of the input attenuator?  While usually less of a problem, one of the
tubes could have a filament to cathode short which would put filament
voltage on the cathode of the tube.
Al
WB9UVJ

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Sent: Tuesday, January 29, 2019 11:00 AM
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Subject: Heath Digest, Vol 97, Issue 9

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Today's Topics:

   1. Heathkit AV-3 Audio VTVM (Richard)


----------------------------------------------------------------------

Message: 1
Date: Mon, 28 Jan 2019 14:31:25 -0500
From: Richard <raitchd at gmail.com>
To: Heath at puck.nether.net
Subject: [Heath] Heathkit AV-3 Audio VTVM
Message-ID: <a417a1f8-7bfc-c6a8-49f8-36902c0c46ea at gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed

I have the above referenced VTVM that is displaying a problem. The meter
reads full scale pegged for all ranges regardless of open or shorted input
or any other voltage input. I recall reading somewhere that this could be
caused by internal oscillation in the meter circuitry. I don't know how to
go looking for that problem.

I would like more information on that problem and how to find it. Also I
would like any other suggestions on what to look for. I have a copy of the
schematic but not the manual or the voltage reference chart that is usually
included with Heath products. If anyone has a .pdf copy of the manual
including the voltage chart, I would appreciate receiving it.

Thanks to all.

Richard

KC9UB



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End of Heath Digest, Vol 97, Issue 9
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