Philips PM2505 electronic meter

[djrm]

I received this meter quite unexpectedly in the post yesterday. It belonged to my late uncle Norman.
I shall treasure it. It just needed a couple of 9 volt batteries to get it working.
Seems to be in good overall condition. I'll be comparing it a HP3478A which I have on loan.
   

[PerdioPal]

Looks like the ohms are linear, good idea and why not as you have some electronics in there, it might take a bit of time to get used to.

[djrm]

Looks like the ohms are linear, good idea and why not as you have some electronics in there, it might take a bit of time to get used to.

Hardest feature to get used to will be remembering to switch it off after use.

Linear resistance measurement is nice to have, just like on a DVM.

Another unusual feature is that the voltage and current measurements are absolute with the polarity indicated on the small auxiliary meter beneath the main dial. .e.e you dont ned to swap leads over to get a reading of negative values. AC measurements don't deflect the aux. meter.

David.

[Mike Watterson]

Must have a constant current source for Ohms?

[djrm]

Must have a constant current source for Ohms?

The voltage amplifier and current source are each half of the only integrated circuit in the meter, a custom Philips part OQ0051. 
Extract from manual found here: https://bama.edebris.com/download/philip...IPS_EN.pdf
   

[Mike Watterson]

It's a lovely design of analogue meter.

I expect a OQ0051 is some regular part. Philips used "house" numbers on quite a few products.

EDIT:
A search suggests the part is only used in this meter and no-one knows what it might be.

[Mike Watterson]

It's got FETs too. So likely very high input impedance on volts?

[ppppenguin]

Nice analogue meter. Most unusually for analogue, and like DMMs, there's no need to worry about polarity.

My experience of OQ parts in Philips SPGs and test pattern generators suggests they were not normally commercially available.

[PerdioPal]

A detailed picture (or two showing both states of polarity) of the auxiliary meter would interest me.
My dead cheap Malpin analogue meter has +/- 5 and 25V ranges, very useful. Done by injecting a weeny current into the meter movement, zero adjusted by the ohms set pot. One of these https://www.ebay.co.uk/itm/186417109229?_ul=GB Maplin were selling them for £9.95 at the end, I bought three.

[djrm]

A detailed picture (or two showing both states of polarity) of the auxiliary meter would interest me.

I have just made a brief video for you showing a variable negative, then positive, voltage being fed into the meter.
See here: https://youtube.com/shorts/9L9c-ygj4cY

10 volt DC supply fed through reversing switch 100K potentiometer driving meter input.
I just happened to have a DPDT switch wired as a reversing switch from something I was testing recently.

The video shows the onset of polarity indication movement as the input voltage is increased, this seems to be independent of meter range, i.e. it always start to move significantly at around 10% of main needle movement.

The service manual I liked to previously has a description of the circuit used.

Test setup:
   

Best regards, David.

p.s.
I tried comparing resistance measurement with the HP3478A and I'm quite happy it is as accurate as the needle interpretation can give.
I must make a meter test box for checking calibrations, I've been given a box full of assorted high-stab resistors of various values.
The meter is averaging only on AC unfortunately but has a bandwidth up to around 30 kHz.