VTVM Battery

[Larry Gauthier]

Yep... I remember. It involved a dropping resistor (470 ohms 2watts, I
think...) from the filament voltage of the tubes fed into a series of three
silicon diodes (part number 57-27 ... heath's favorite diodes - 600v @ 1
amp - but could any silicon diode), with a 200 mfd capacitor between diodes
#1 and #2. The thought was that the first diode acted as a rectifier, the
cap filtered the half-wave rectification, then the next two diodes in series
acted as a 1.2 volt zener diode (.6 volt drop across each diode). So, this
was essentially a poor-man's constant voltage source that looked like a 1.5
volt battery.

It was marginal on the lowest ohm's scale where the highest current was
drawn, but you could zero it out...

-larry gauthier
wb8bgo
one of the former hams from heath
{{egads... the fact that I remember the diode part number from 30 years ago
is frightening!! -}}


-----Original Message-----
From: Neil Morrison <morrison at T-III.COM>
To: HEATH at LISTSERV.TEMPE.GOV <HEATH at LISTSERV.TEMPE.GOV>
Date: Monday, September 27, 1999 1:35 PM
Subject: Re: VTVM Battery


>Which issue of Radio Electronics?  I have most of mine back to the 60's.
>Neil
>
>> -----Original Message-----
>> From: Malcolm Leonard [SMTP:rosinfumes at YAHOO.COM]
>> Sent: Saturday, September 25, 1999 4:46 PM
>> To:   HEATH at LISTSERV.TEMPE.GOV
>> Subject:      Re: VTVM Battery
>>
>> --- Allen Bush <AE0Z at COMPUSERVE.COM> wrote:
>> > Back when I worked at Heath in St. Joseph in the
>> > late '70s I remember they
>> > had a modification used "internally" in service
>> > dept., etc. for eliminating
>> > the 1.5v "C" cell that their common VTVM's used.  As
>> > I recall, it consisted
>> > of a diode, a resistor, and a capacitor.  It was
>> > written up in one of
>> > Heath's internal tech notes.  DOES ANYONE RECALL THE
>> > PARTICULARS OF THIS
>> > MOD?  It seems it may have affected performance a
>> > bit on the lowest Ohms
>> > scale (may have had to reset zero for that range?)
>> > but otherwise worked
>> > great.
>> >
>> > I would sure like to install this in the several
>> > VTVM's I have, and others
>> > might as well.
>> >
>> > Allen Bush, AE0Z
>>
>> Hi1
>> To anyone who sends me an SASE  and one dollar I can
>> supply a hard copy of such a circuit.Mine is from an
>> old Radio Electronics magazine,and while I haven't
>> tried it yet,
>> I know someone who swears by it,not at it!The dollar
>> covers my time traveling to the copy shop.etc.
>> rosinfumes
>> Malcolm Leonard
>> 165 Canfield Ave.
>> Warwick,RI 02889-8858
>> >
>> >
>>
>>
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