The U meant The United Kingdom.
If the vtvm voltage is the same measured at the top of both cathode resistors, the meter movement will measure zero due to there being no current flow between them.
The chassis ground is at approximately half-way between the positive and negative rails allowing for a negative voltage of -70 volts to be applied through a balancing resistor network to the cathodes of the tubes.
On the circuit board are calibrating potentiometers.The V-7 vtvm vtvm was only made in 1956 and the V-7A was manufactured from 1957 to 1961.All these parts can be obtained at Radio Shack.It has been reassembled manual from my copy (saved when the site was live) together with files retrieved from chive.IM-11 and, iM-18 heathkit in a similar way.I have modified.Take the.5-volt battery and measure the exact voltage with the digital meter and put the vtvm on the.5-volt scale.Many of the files here are just schematic diagrams but some include additional information such as specifications, heathkit and a few are complete manuals.I got this vtvm for almost nothing but all the parts seem to be there except for the shielded vtvm probe.The only thing manual that needs to be done is constructing a high impedance probe to get accurate readings.Among them was the.Insert test probe leads in the common and AC/Ohms jacks.The circuit board is sandwiched manual between this battery holder and the chassis.It was the successor of the V-7 that was only produced during 1955, that in turn was the successor of the.Drill holes and install as shown in the picture above. The original DC voltage probe that came with this meter consisted of a phono plug connected to a shielded cable with a probe on the end housing a 1 megohm resistor inside.
I came up with the idea of making an adapter for this meter so that generic meter leads could be used for all the functions, AC and manual DC voltage, plus resistance.
The 70 volts that this vtvm was designed to work with would rise to about 90 volts which could cause the meter to give improper readings.
In my book heathkit sold on Amazon, "Getting the most from your pack multimeter" by mr electro, I get into the history of the multimeter and vtvm and how to use them and the modern divx digital meter.
Obtain a digital meter that reads accurately and use this as your reference.
Let the meter heat up for about 30 minutes and plug two generic meter leads into the adapter.The twin triode has vtvm a filament wiring arrangement so that it can be run on 6 volts.As a new, isolated from the chassis, battery holder I use a plastic film-canister for ordinary film type 135.It's installed with a standard "C" cell with the negative terminal touching the spring and the positive tip touching the screw inside the holder.Its attached to the chassis by a small nut and a metal bracket.The vtvm (Vacuum Tube Volt Meter).If you have anything to add please email paul (at) vintage-radio (dot) info.In 1961 the, v-7A was replaced by the, iM-11.In the late 1950's to early heathkit 1960's, it was routine for TV repairmen to replace the large and bulky selenium rectifiers that were found in 1950's TV's to replace them with much smaller silicon diodes with a thermistor in series with them.Once heathkit inside, secure it with some hot melt glue.It would be a good idea to clean the screw head with a pencil eraser codec and the surface where the negative part of the battery touches the spring.The V-7 is featured and it's explained how the vtvm still has a useful place on the modern workbench.Make sure the part with the inside thread is the one that's sticking out.