Admirable AVO

marconi · May 10, 2021

When a relative’s husband died and she cleared out her loft she found an old AVO in a leather box. I don’t know how old it is but know it has not been used since her husband left the RAF In the 1950’s. ( I think it may actually belong to them!) It needed a good home so I was given it. I have not got round to cleaning it up and sorting out the missing batteries and it has just sat on the corner of my bench. Yesterday I needed an old fashioned moving coil meter to observe a voltage variation. I compared its output against my trusty skytronics DVM and to my pleasant surprise observed what I recorded in the attachment. Please excuse some of the camerawork. I guess it must be 60 to 70 years old.

ps: My first meter bought as a Christmas present in 1971 which my father was told was the Japanese equivalent of an AVO. It certainly gave sterling service until the rotary switch wore out.

Analog Multimeter TMK-500 Equipment TMK, Tachikawa Radio - https://www.radiomuseum.org/r/tmk_analog_multimeter_tmk_500.html

Wilko · May 10, 2021

Awsome.
Very nice way to start the day !

Lucien Nunes · May 10, 2021

Over on the vintage radio forum are AVO experts who are usually keen to acquire serial numbers and data for the register.

I still have the Model 8 Mk.II that dad gave me, worn and damaged in places but still fully functional. I don't use it any more, I have a couple of later ones that were maintained in calibration until the 1990s that don't have any sentimental value. It's useful to have a couple of moving-coil meters on hand when working on machines, and I keep a set of shunts in the drawer although they don't come out often.

Doors are closing behind us for maintaining moving-coil instrument because the skills and tooling to service the movements are in very short supply now. The AVO Valve Characteristic Meter is a case in point, as it uses a very sensitive (30μA FSD) movement, even more sensitive than the multimeter. The last company that would repair and calibrate them have stopped offering the service and the chap who had the experience and knowledge is no longer alive, so now we're on our own. It can be worked around by using a more modern movement and a buffer circuit that matches the original sensitivity and resistance, but the machines themselves are valuable and more so with the original meter in place. There is a pair of protection diodes to hopefully save the coil from destruction if the controls are set wrongly but they can't protect against 100% of all possible mishaps.

It focuses the mind when dialling in the settings.

Lucien Nunes · May 10, 2021

Testing audio valves on the dining room table, a while back:

marconi · May 10, 2021

Lucien: you must have a very understanding wife or you live alone.

Lucien Nunes · May 10, 2021

This is specifically the dining table at the family home which is a bit more flexible re. comings and going of electrical apparatus. The room at that time contained a working resistance dimmerboard for the lighting, a mercury arc rectifier, an Aeolian roll-playing Orchestrelle, six models of Goblin Teasmade, various cameras and projectors, even an AVO meter or two.

marconi · May 10, 2021

You do live alone or your wife has simply given up - wise woman.

marconi · May 10, 2021

Messages overlapped.

Marvo · May 10, 2021

I have a couple of old Evershed and Vignioles constant pressure/insulation testers. Iwas also toying with reconditioning them but was struggling to find suitably skilled people and suitable components so I ended up leaving them as they are.

marconi · May 10, 2021

Marvo- If ever you are stuck for a place to store them..........

Lucien Nunes · May 10, 2021

I have one from about 1908, not that long after they coined the 'Megger' name, that is still usably within calibration. I think the voltage is a slighly low on account of the generator losing magnetism but really not very much, and it's within cal for the actual resistance reading. The magnet could be re-charged to bring it fully back in-spec but as it is still sealed with a proper lead seal, I don't want to open it.

Lucien Nunes · May 11, 2021

You do live alone or your wife has simply given up - wise woman.

We're not married, but in any case this pic is an old one, taken before we met.

marconi · May 11, 2021

I admire your dedication to preserving old electrical artefacts and equally the technological knowledge associated with them.

Thought: could you do the same with telectrix and Pete999? ?

telectrix · May 11, 2021

marconi said:
I admire your dedication to preserving old electrical artefacts and equally the technological knowledge associated with them.

Thought: could you do the same with telectrix and Pete999? ?

no bloody chance. he'd have us pickled in brine and put on display in his museum.

littlespark · May 11, 2021

He can’t be living alone, or those curtains would be his choice.

Lucien Nunes · May 11, 2021

pickled in brine

Formaldehyde, probably. Or stuffed. One hunched over a hole in the skirting stripping VIR singles, another with a wooden-handled screwdriver wiring a pendant with maroon twisted twin. Display titled 'Fitting the Electric Light c.1930'

telectrix · May 11, 2021

Lucien Nunes said:
Formaldehyde, probably. Or stuffed. One hunched over a hole in the skirting stripping VIR singles, another with a wooden-handled screwdriver wiring a pendant with maroon twisted twin. Display titled 'Fitting the Electric Light c.1930'

can tell who's who from that. I can't get on my bad knees and pete can't climb. means we need to pay 2 apprentices out of pensions (that's if there's a bit left over from the beer kitty).

pc1966 · May 11, 2021

Lucien Nunes said:
Testing audio valves on the dining room table, a while back:

KT66 or KT88?

Lucien Nunes · May 12, 2021

Mostly KT66, although it looks like there are a few KT88s at the back (with the metal bases). I can see also a bunch of 5U4s, 6SN7s and various odds. The VCM is now in the museum workshop area and I am supposed to be testing some 1930s US audio triodes for someone, but it's proving an uphill struggle to get me, the valves and the tester together for long enough.

For the younger readers, valves are what we used before transistors as the main active component of all electronics. They were generally quite reliable and rarely needed replacing in ordinary applications; many valve radios for example are still working with all their original valves despite having needed most of their capacitors changed. But valves can and do fail especially if there are faulty capacitors in their surrounding circuitry that drive the valves into overload, and eventually wear out if used heavily. Valve behaviour is quite complex and there are many different kinds with vastly different specs, hence the rather elaborate machine needed to test them properly.

pc1966 · May 12, 2021

Lucien Nunes said:
They were generally quite reliable and rarely needed replacing in ordinary applications; many valve radios for example are still working with all their original valves despite having needed most of their capacitors changed.

The two Voyager craft use valves for the transmitters (X-band TWTs) and they are both still working after 43 years of continuous use under "interesting" conditions!

telectrix · May 12, 2021

pc1966 said:
The two Voyager craft use valves for the transmitters (X-band TWTs) and they are both still working after 43 years of continuous use under "interesting" conditions!

so you watched Star Trek The Movie as well?

DPG · May 12, 2021

Believe it or not, even into the 2000s many of the police radio transmitter sites were still using an RF transmitter with a valve as the final amplifier. Didn't look very 'valvey' though as it was sleeved with a metal heatsink. Can't remember the type.

This was prior to the Airwave digital system being installed.

Lucien Nunes · May 12, 2021

Nothing wrong with valves, still a popular technology; you've got one in your kitchen.

I have a couple of big'uns that you might have had some use out of without knowing it. Prior to the digital switchover in 2012, if you watched BBC1 on analogue in London / South East the signal was coming from a pair of 40kW Harris Sigma transmitters. It was the control unit for those that we saw Mark Thompson switch off ceremonially to mark the end of 75 years of analogue TV in London.

You might be able to guess where one of the transmitters ended up. They didn't let me take the mast, apparently that's still in use.

London analogue TV signal switched off

Analogue television is switched off in London, 75 years after it was first invented.

www.bbc.co.uk

Zerax · May 12, 2021

Lucien Nunes said:
We're not married, but in any case this pic is an old one, taken before we met.

Managed to find a pic of the same dining room shortly after they met...

telectrix · May 12, 2021

Zerax said:
Managed to find a pic of the same dining room shortly after they met...

that's nothing. my missus insists on placing a vase of flowers or some other tat directly in front of the TV's remote sensor, so you need to be a contortionist with the hand unit. then says it's my fault she can't switch from Emmeroids to Eastidiots, to Constipation Street.

Lister1987 · May 12, 2021

telectrix said:
no bloody chance. he'd have us pickled in brine and put on display in his museum.

Surely your brain already pickled Tel?

telectrix · May 12, 2021

Lister1987 said:
Surely your brain already pickled Tel?

brain was pickled in 1975 ( i got wedded to the Poison Dwarf). OK now she's long since gone. brain back to normal state of useless.

Lister1987 · May 12, 2021

telectrix said:
brain was pickled in 1975 ( i got wedded to the Poison Dwarf). OK now she's long since gone. brain back to normal state of useless.

I wouldn't say that Tel, "I'm not completely useless, I serve as a shining beacon in how NOT to do things"
?

Mike Johnson · May 12, 2021

Lucien Nunes said:
We're not married, but in any case this pic is an old one, taken before we met.

I don't think any self respecting woman would have put those curtain up. ?

telectrix · May 12, 2021

maybe it was a condition of sale thea the buyer took them off of the vendor's hands.

marconi · May 12, 2021

I’d like to move this thread away from the world of Laurence Llewelyn Bowen by asking who do we think the apprentices telectrix and pete999 employed in the 1930s might be now in the EF and why?

pc1966 · May 12, 2021

DPG said:
Believe it or not, even into the 2000s many of the police radio transmitter sites were still using an RF transmitter with a valve as the final amplifier. Didn't look very 'valvey' though as it was sleeved with a metal heatsink. Can't remember the type.

It is still very much the case that for very high RF power levels, and/or very high frequencies (in the 10s of GHz and above, not "VHF") that valves are still the best choice in many cases.

Of course when ever you ask for the "best" choice it is very dependent on the criteria you are using for it, and the trade-off changes as technology advances, but they still have a very special place in some areas.

littlespark · May 12, 2021

I once worked at Leuchars when it was an RAF base. Doing some not very interesting mundane work in their communications centre.
3ft thick bomb proof concrete walls.

A lot of their equipment still used valves as it wasn’t able to be hacked as well as modern digital electronics could

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