If you are working on a VTVM of any type remember it is a 120 volt or maybe 220 volt powered instrument and you can get a shock . You could also be injured by the voltages in a VTVM meter SO be sure to UNPLUG THE VTVM before working on it ! This is a HEATHKIT IM-13 VTVM Bench model VTVM made in 1963.
A very good instrument for an electronic workbench it appears to be the factory built model because of the very good assembly and the fact there is no heathkit sticker on it . A VTVM or
vacuum tube voltmeter has a very high impedance input the Heathkit VTVM's have an 11 megohm input so they do not load down the circuit . Every service bench and engineering workbench at Heathkit had at least one VTVM and when aligning Heathkit equipment it is best to use a Heathkit VTVM . I recently aligned the phase locked loops for the HFO oscillators on a Heathkit SS9000
tranceiver and it did not work right . I realized I was using a plain old VOM meter . I did the alignment over again using a Heathkit VTVM and the SS9000 works great . testing the VOM and VTVM both on the same circuit the VTVM was giving a different reading .
The diodes I used to make the battery eliminator circuit actually measured .7 volts drop across each one making the voltage of the battery eliminator circuit 1.4 volts . So my statement that the diodes have a .6 volt voltage drop is an error these diodes actually have the .7 volt drop . One last thing the parts for the battery eliminator are very non critical the capacitor need not be 100UF it can be up to 500 UF and any voltage over 20 volts . The resistor can be any value up to 39 ohms . I did a couple of these using 39 ohm 1 watt resistors and they work fine . The diodes I used on this one were common 1 amp black plastic diodes from a hamfest .
Re-alignment was then done for OHMS due to the voltage difference between the battery and the battery replacement circuit.
73 Bob
