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Philips GM6004 Voltmeter (1951)

GM6004-front.jpg
The Philips GM6004 is a valve voltmeter. It has a differential amplifier circuit using two penthodes. This is probably a /02 version, using Rimlock valves.
Philips called the GM6004 a Diode Voltmeter. It is a valve voltmeter with built-in signal rectifiers.


	  Principle of operation: two-pentode bridge.

Principle of operation: two-pentode bridge.

The design is clever. This VTVM uses a bridge circuit with two pentodes. Two EF40 pentodes are used as a cathode follower. The use of pentodes should result in a better linearity than with a VTVM using triodes, such as the Heathkit V-7A. A bridge circuit such as this had the advantage of compensating temperature drift. For AC voltage measurements, a probe with a built-in rectifier is used. The GM6004 has a rectifier diode in the probe and one in the VTVM itself. This allows for peak-to-peak AC measurements. The ranges are:


  A view from the back.

A view from the back.

The valve line up is:

I bought this meter in 2008. It was in reasonable condition but the case had been painted creamy white. Originally, it has a hammered metal finish case which dates it in the 1950's. The original version is from 1949 and used EF6 penthodes. The /02 version dates from 1951 and has EF40 Rimlock penthodes. This specimen seems to be from around that time. There is something like a date code on one of the potmeters that seems to point at 1950. Someone has scribbled a note on the chassis that says the instrument was ok (callibrated? ) in 1953. Looking inside, I saw the chassis looked well, but the power electrolytic had been leaking. Need to replace that one, and remove the white paint.


  A closer look at the components on top of the chassis.

A closer look at the components on top of the chassis.

I will fix it later on

Copyright © 2008 by Onno's E-page         published 2008-10-24