Post office test meter 12C
 

Hi there

I've been looking on the forum trying to find out something on this meter.

If anyone could shed a little light, I'd be REALLY grateful. Just bought it after reading what others had said on here about P.O / AVO meters.

This will be my first analogue meter :)

Re: Post office test meter 12C
 

There's a bit here on 12/B but not much data on most GPO test meters anywhere.

http://www.dustygizmos.com/arcpages/arctest.htm#GPO

12B/1 Multirange

Re: Post office test meter 12C
 

What did you want to know? General rules, start at the highest range and work down if needed, and avoid get the polarity wrong when testing DC!

Check and see if the battery/batteries have leaked. These designs are a little prone to damage as there isn't much stopping the leak spreading onto the circuit board.

Dave

Re: Post office test meter 12C
 

This version was based on the GEC Minitest, some others were AVO or Taylor based.

Re: Post office test meter 12C
 

Thanks for the replies
I did wonder if manuals were available. Realise most analogue meters are pretty similar.

One thing I would love to know is when this was manufactured, 60s/70s?

Re: Post office test meter 12C
 

I've got one of these - I think mine was manufactured in 1973. The instruction plate on the back has the legend "12B R.P.B 73/5". I've no idea what R.P.B stands for, I'm afraid.
Mine is identical to yours, except for the panel lettering which shows "P.O. M.M-R No.12B". I can only assume yours is a later revision, since yours shows "No. 12C". I think the manufacturer was SEI (Salford Electrical Instruments - later taken over by GEC).

Should you need to get inside the meter, there are two screws concealed under the instruction plate. This is glued in place, so you will have to carefully peel this up with a thin blade. Double sided tape will stick it on again.

Nicely made inside - all I had to do was apply a wee bit of contact cleaner/lubricant to the AC/DC toggle switch and the track of the ohms adjust pot. It gets used most days, and is my first go-to for quick non-critical measurements. Accuracy is OK, but AC measurements are a bit out - it reads about 10% high on the 250 VAC scale.

Re: Post office test meter 12C
 

Raptornet, did your purchase come with a leather carry-case? If not, once you've established the meter is working let me know the dimensions-

It's feasibleIi have a PO case that will fit it- you can have it for the price of postage.

(It's intended for a 12D/1 but the 12C may be the same size.)

Dave

Re: Post office test meter 12C
 

It did come with a case, but it's seen better days and the clasp is bust

Re: Post office test meter 12C
 

BTW it works. Would it be wishful thinking that there might be a manual for this or a similar model?

Re: Post office test meter 12C
 

Finally cracked open the meter to look at the battery compartment. Oh boy, an Ever Ready B154 and Vidor HP7 sit in situ. The HP7 was just aweful.

Luckily the contacts were not eaten away. Have cleaned them down with alcohol.

Question, what is a 15v B154 and can I get a replacement?

Re: Post office test meter 12C
 

You can get B154 replacements (at a price) several vendors on Ebay for starters.

Rolling your own with a stack of button cells is another way to go.

Re: Post office test meter 12C
 

Fantastic! Don't know why I didn't think of using eBay. Managed to source one. Can't say I've seen a 15v battery before.

Re: Post office test meter 12C
 

Here's the case i mentioned

The thin strap is 'abbreviated' but the remains of it latch together.
The clasp works.
The thick strap must be so you can use the meter without taking it out of it's case.
It weighs 500grams (!) but it's so tough it won't need too much packaging.

interior- H a shade over 5"
W 3 and 3/4 inch
D 2 and 3/4 inch (plus the leads compartment)

Dave

Re: Post office test meter 12C
 

Also 8 or 9 stitches have pulled at the top of the back, where they are under strain when the flap opens all the way. So serviceable but scruffy.
dave

Re: Post office test meter 12C
 

Dave that's great, can I have it please? Looks almost identical to the one that came with mine, just a lot better nick. The metal parts on mine are rusted to hell.

Re: Post office test meter 12C
 

Yep! Will work out postage and do a private message to you.

Re: Post office test meter 12C
 

Great stuff, can anyone tell me if there is a manual for these any place?

Re: Post office test meter 12C
 

Well I now have what appears to be a fully working multimeter, I’m having to learn how to read this beast as it’s totally different to the LCD meters I’m accustomed to.

Re: Post office test meter 12C
 

...Principally: Avoid reverse polarity on DC (if polarity is not known use the highest range possible) Generally speaking starting on a high range then working down as needed is the way to avoid damage...whatever current or voltage is being measured. Portable Meters are generally calibrated with the scale facing upwards.

There was a slightly better case for sale cheaply on ebay i noticed just after i sent this one to you- Murphy's law!

Dave

Re: Post office test meter 12C
 

Are there any good guides on analogue meters? I feel I kind of have the basics, but wouldn’t mind watching a video or reading something that educate the grey matter.

Isn’t that always the way! Nah this case is fine, I’m actually considering reviving the one that came with the meter. The strap and buckle is the only part that’s really jiggered on the thing, wondering if a cobbler might be able to help craft something.