More Laboratory Testers

Valve voltmeter, Dawe Type 613C

 These used to be employed when only a very high impedance load could be tolerated by the item being tested. There were a few problems. If the signal being measured had a pure sinewave waveform the reading would be true RMS otherwise the reading would be relative i.e. One could peak something up or tune something out but you couldn't guarantee the voltage reading to be valid. Most waveforms met in practice would have a degree of distortion or had a harmonic content. This example measures voltages in 6 ranges from 1V to 300V and via a toggle switch the ranges change to cover 1mV to 300mV.

Audio Signal Generator, Solartron OS101

 This piece of equipment is built like a battleship. It weighs something like half a hundredweight and according to little markings on the dial of the meter dates to 1955. Frequency coverage is 25c/s to 250Kc/s and of course predates the move to "Political Correctness" of scientific units.

Inside reside four small B7G valves and a larger 5Z4G rectifier. Although these equipments were very stable and accurate it used to take some time for them to warm up and meet their specification. Usually they were switched on at the start of the day otherwise an engineer would have to make the tea before proceeding with his work while the meter stopped wandering up the scale.

This example is a 19" rack mounting type fitted in a standard case. Unfortunately it's been stored in damp conditions resulting in deterioration of the finish.

This impressive piece of British Engineering was used by a friend of mine who makes microphones in the neighbouring village of Burley in Hampshire. The "Muirhead" style slow motion dial has a standard cursor at the top plus a vernier at the bottom. The latter could be used for resetting to a specific dial reading so that batches of items under test could be checked at the same frequencies.

AVO "All Wave Oscillator"



Before cleaning


After cleaning

Universal Bridge


 This is a Marconi TF868/1 used for measuring Resistance, Capacitance and Inductance

Somewhat larger and more consuming of power than the latest hand held LCD multimeters but in the 50's, 60's, 70's and even much of the 80's you didn't have a lot of options. It was either the trusty AVO, or one of these if you wanted to look the part. It came from the same place as the OS101.

Ranges were quite decent and like other Marconi instruments the design is well thought out;

Resistance:- 0-10/100/1k/10k/100k/1M & 10Mohms

Capacitance:-0-100pF/1000pF/0.01uF/0.1uF/1uF/10uF & 100uF with tan delta

Inductance:- 0-100uH/1mH/10mH/100mH/1H/10H & 100H with Q

The principle of the bridge requires the meter to be dipped using appropriate delta or Q settings with capacitors or coils.

Measurements of resistance are made at DC whilst C and L are measured at either 1KHz or 10KHz and measurements to 3 significant figures are readily made.

Not that easy to use otherwise why would they written all the instructions on the top!

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