Insulation Test Unit P T F 685/2

[Julesomega]

I have just bought this test unit online, and am immediately struck by several oddities:

It was sold as a Marconi item, and has a superficial likeness to some MI items from the time, but there is no mention of that company anywhere on or in the instrument. I am reminded of other pieces of equipment that I had mistakenly ascribed to the wrong maker. MI did have a very few accessories with type numbers PTF, but not spaced out like P T F here.

The photo of the front made it look like the MI early solid state models, so I was expecting to find a fold-out PCB populated with TO18 devices. This unit is much simpler, having only one wire-ended EHT rectifier diode, type U37. The Valve Musem dates this as introduced in the early 1950s with only a short production life.

My unit has been heavily mod'd, bearing Dymo labels showing "Modified 500V only" and the rotary selector switch has been replaced by a toggle switch for ON/OFF. The original switch gave selections of testing voltage Off-500V-750V-1000V-1500V-2000V by switching taps on the mains tfmr. The U37 has been snipped from the supply and an anachronistic 1N4000 type substituted.

The co-ax test currently emerges from one of two holes on the front panel, so I'm wondering what was in the 2nd hole: maybe a press switch for applying the test voltage.

Has anyone seen a similar instrument?

[Silicon]

I wonder if PT stands for Pot Test (as in Hi-Pot Test).

Maybe the F stands for Farnell.

[Radio Wrangler]

Meter, knob and mains neon all look Marconi Instruments. It might not have been a sold product but some production line/ quality control in-house test equipment

David

[turretslug]

Production Test Fixture?

[Dickie]

Originally Posted by turretslug

Production Test Fixture?

Exactly. It's a one-off test jig built for production test and uses whatever ready made parts the designer/builder could find. You are unlikely to find any information on it.


There's a lot of stuff like this around online at the moment as all the Marconi/IFR/Aeroflex factory test gear got auctioned off to dealers a while back. Beware of cases that look like complete instruments but are only incomplete factory test hulks!

[Julesomega]

[QUOTE=Dickie;1554115]

Originally Posted by turretslug

There's a lot of stuff like this around online at the moment as all the Marconi/IFR/Aeroflex factory test gear got auctioned off to dealers a while back. Beware of cases that look like complete instruments but are only incomplete factory test hulks!

Funny you should say that - this has some very IFR-ish stickers.

Thanks for all the replies, I'll just have to work out the circuit and try to get it back to original. Pity they left the heater connected, hope that U37 has some life left, though there are plenty of later equivalents available.