AP5526 voltmeter

[Andrew Sinclair]

Hello,
I am building a valve test panel for the HMS Collingwood museum to a 1920s design. The panel used an AP5526 voltmeter on it's 25V range, as a milliammeter to measure anode current! I think this was an instrument that was readily to hand throughout the fleet, hence the strange method of use. The anode currents for the various valves are quoted as voltage readings.
I do not have one of these instruments, so I don't know what the full scale deflection current was.
If anyone has an AP5526 voltmeter, could they measure the full scale deflection current on the 25V range and tell me what it is please? (Probably the same FSD on all ranges) I am sure I can knock something up using panel meters I have here for the museum to use. We are currently restoring a 1926 LF receiver for display/demonstration and I would like to make up the valve tester they would have used on board ship.
Andrew

[Ed_Dinning]

Hi Andrew, I'm not familiar with this instrument, but on the lower edge of most meter dials there is often the meter sensitivity figure in mA or uA.
Working backwards with ohms law and you should get the information you need.

Ed

[Andrew Sinclair]

Thanks for the reply Ed.
I don't have this meter either! I have seen pictures of it on the web but there is no meter FSD or coil resistance marked on the scale plate. I had hoped that a forum member might have an AP5526 meter and would kindly measure it for me.

[David Simpson]

Hello Andrew, It's good to learn that the HMS Collingwood Museum is still running & forging ahead with T/Eq. projects. That'll please a few ex Tiffies in the VR fraternity. There was a rumour going around that, like RAF Henlow's museum, Collingwood was under threat.
Would you be able to download a picture of a voltmeter that you 've seen on the web ? Moving Iron I assume ?
Incidentally, scan down this T/Eq. forum page & you'll see another chap is also searching for a MI meter for his 1930's set/valve tester.
Could you post a copy of your circuit diagram please ? I'm guessing a DC design.
In recent years I've been testing a number of immediate post WW1 triodes for an early 1920's Marconi collecting BVWS enthusiast chum. Bright Emitters, Dull Emitters, and Cruciform design. They're rocking horse manure in value, & fragile. But surprisingly, still work jolly well Ia & Gm- wise.
Have you had a shufti through the massive VMARS online archive for gen on the AP5526 Voltmeter ?

Regards, David

[Andrew Sinclair]

The Collingwood main museum closed, but the old HMS Mercury museum is still on-site. We have been adding to it recently... We have most of the equipment working and demonstrate it on open days and to navy classes coming through he establishment.
I am restoring an outfit CJ receiver, which consists of an A11 tuner, M11 amplifier and K5 heterodyne. It tunes 12kHz to 550kHz and dates from 1926. I don't know of a working example anywhere. I thought it would be nice to have the period valve testing equipment to check the valves are OK from time to time. The attached file is from the 1930 edition of BR222 with updates from the early thirties.

There are two testers shown. The simplest applies 50V HT and LT supplies and measures the anode current with grid strapped to 0V. I think this is a crude "emission" tester. The document gives typical readings for Naval valves. The AP5526 voltmeter is probably a milliammeter with series resistors to give 5V 25V and 250v ranges. I have attached a picture from the web. I would like to know the FSD current of the milliammeter. There is nothing on the VMARS website. Tests on slightly later 2V battery valves show currents of around 0.5-1.5mA for a small signal valve.

The more complicated test panel looks more useful as it measures gm and Ra, I would need to do some experiments to find the resistor values as they are not given. I have my work cut out restoring the rest of the receiver at the moment, so the simple tester appeals!

[David Simpson]

Ahoy again Andrew,
Many thanks for the attachments. In return, I've attached a copy of an old report from a former Collingwood Museum C/O from yesteryear. He'd be proud of your 21st century ambitions. Think I acquired it from the late Dennis Tabor who would've been the UK's most prolific valve tester collector & expert.
I've only ever spoken with him on the phone, but I think that Ed Dinning has actually met him(? Ed). I believe that Dennis's collection was sold off, but I wonder what has happened to all his old documentation. That should be in a Museum now. I hope it hasn't been skipped.
I was in touch with Collingwood several years ago, during my search for an old BBC VT-4 or VT-5 Valve tester from 1939, even just it bits. But no luck, sadly. I'm still on the hunt.

Regards, David