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VACUUM-TUBE VOLTMETER
» HEATHKIT  IM-11/D «


The picture shows on the right the HIGH-VOLTAGE (x100)-PROBE,  Max. = 30 kV

V A C U U M - T U B E  VOLTMETER  » IM-11/D «  Self-Assembled  » HEATHKIT «
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German Version by DAYSTROM GmbH, Sprendlingen b. Frankfurt am Main ( 1963 )

Voltage Ranges:   0 .. 1.5 ;  5 ;  15 ;  50 ;  150 ;  500 ;  1500  V  DC/AC

Resistor Ranges:  (x1); (x10); (x100); (x1000); (x10k); (x100k); (x1M) Ω

Resistor Battery: 1.5 V  "Baby Cell"  ( C )

Input-Resistance: 11 MΩ;  Precision: 3%(DC)/5%(AC);  Power: 220 V AC ; 10 W   

Dimension  ( W x H x D )  4_3/4" x 8_3/4" x 5"  /  12 cm x 22 cm x 13 cm

The  » IM-11/D «  DIAGRAM ...

R E M A R K S :                  Why a VACUUM-TUBE VOLTMETER  =  "VTVM" ???
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An AMPERE-Meter has to have a very low inner resistance "R-Instr"  - and  a
VOLT-Meter has to have a very high inner resistance  -  specially, when the
inner resistance of the object to be measured is high.      E X A M P L E :

Let the voltage on a vacuum-tube be "true" +50 V, than the inner resistance
of this vacuum-tube is  0.5 MΩ ...

             

Measuring the VOLTAGE ON THE TUBE with a VoltMeter has the effect, that the
total current splits:  I-Total = I-Object + I-Instr.

Case (A)
--------
A "normal" instrument with  1 kΩ/V  in its 100 V Range, connected parallel,
will result in  a   0.5 MΩ || 0.1 MΩ  =  83.3 kΩ   a small resistance!  The
measured voltage  Ux  we get out of the proportion ...

   Ux / 100 V   =   83.3 kΩ / ( 500 kΩ + 83.3 kΩ )
           Ux   =   100 V * ( 83.3 kΩ / 583.3 kΩ )   =  14.3 V

A very bad result!  As higher "R-Instr", as more precise the measurement...

Case (B)
--------
A "VTVM" has a high inner resistance,  eg. 11 MΩ ...

   0.5 MΩ || 11 MΩ  =  0.48 MΩ    only  4% less,  makes a better result !

In the 60's, this "VTVM" was a hit:  Who had to repair  vacuum-tubed RADIOs
or TVs needed a VTVM.  I bought this as a KIT for self-assembling/soldering 
in 1963.  Have a look at a  DETAIL IN ITS MANUAL:  WIRING THE SWITCHES ...

   

After a plastic knob broke, I replaced both with  METAL KNOBS.  Since then,
this  »IM-11/D«  is reliable, durable and in use 50 years! In 80's I bought
additional a modern DIGITAL-VM ... It failed after the warrant was over !!!
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                   Have a look at an Analog "SOLID STATE" MultiMeter
impressum:
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© C.HAMANN        http://public.beuth-hochschule.de/~hamann        04/04/14