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Old 29th Dec 2019, 11:02 pm   #1
donutty
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Default Anko T72 'tube' tester - loadsasockets!

Here's something there isn't much information about - the Anko 'Teletest' T72.

I picked this up a few months ago while on business near Chicago.

I've wanted an American 'tube' tester for a while as every time I go over to the 'states I bring back an old radio. This time a nice little Detrola accompanied the Anko tester. A Zenith the time before that. An RCA before that etc. etc.

Out antiquing in western Illinois I visited a few antiques shops and kept my eye open for valve testers. 3 shops under my belt; no luck. On my previous trips when I hadn't been looking for one, I saw them quite regularly. Of course now that I want one they start hiding!

I went into a little old antiques shop that I nearly didn't bother with because it looked not quite my type (architectural, clothes, 'old lady stuff'). Upon entering the old-ish lady asked "can I help you with anything?" but as I doubted the place would have anything interesting I said No and had a browse. Only an old siezed up Olympus 35mm and some pin badges. Get a badge, get going. On my way out the same lady asked "so what sort of things are you going around looking for?". I replied "Old cameras (yes I've seen that one), radios, technology stuff, signage..and I've been on the look out for a tube tester.."

"A tuuube tester??... you'll never believe your luck.. just wait right there; I have one in the back room!!"

She fetches out what looks to be a tatty old yellow suitcase. "This is normally out on the shop floor but nobody seems to be interested in it so I put it away for a while".

On to the counter it goes and I open it up and have a look. 6V6. Yep. 12AX7. Got it. 12AU7. Indeed. That checks out for me. Yeah I know they all have European equivalents so why did I need an American tester? - They were the only ones I could think of on the spot. The price? $40. Write it up! It was $60 before she put it away she said, but gave me a discount because she loved the way the sale happened.

So I learned that if somebody asks you what you are looking for... tell them! I could have easily walked out of there with a shrug of the shoulders thinking it was all vintage coats and butter churns. Instead I walked out with the 1950s beast you see here. And no, I didn't see another tester all trip (another dozen antique stores visited).

Anyway... I digress but thought the story behind it was quite spooky. On to the meat:



As I said at the start of this topic, there really is very little information about these. There seem to be 2 or 3 smaller siblings (52 sockets etc.) all in the same yellow lacquered tweed case that are either in people's possession or have been sold on eBay or reverb.com but no schematics, manual scans or, bar the photos on Radiomuseum, details of what is inside.

Cracking it open is a 12-screw affair. A hefty transformer sits inside along with a 502A thyratron, a multi-tap WW resistor, a silicon rectifier, a dry electrolytic cap (dry by design, not as in dried-out), various resistors and support components, some non-user-accessible potentiometers and trimmer caps probably for factory calibration.....and.... the back ends of 72 valve sockets!

Oh, and also the remains of the crispy crunchy mains lead that I removed in my hotel room without the aid of a cutting implement. Just my bare hands!

Swapping the perished input lead for a more modern example I hooked it up to my 120V USA step-down transformer, via a lamp limiter, gave it one final eyeball and flicked the swith. Nothing. The 10W being pulled by the transformer did not raise at all. No lights. No magic smoke. A let-down.

There was a panel mounted fuse. Whip this out. It's open! Maybe somebody plugged it in back in the states with that crispy mains wire and blew it. Right, a new one in; it's going to work now.

Nope. So I started to trace the wiring and cobbled up a little schematic of the input side of the circuit. Buzzed out the fuse holder, power switch, resistor. All OK. Next port of call is the transformer. I sure hope its OK as I'll more than likely never get another one. All my tests confirmed that the primary winding was open. Drat.

During my exploration I had noticed three unused wires going to the primary side of the transformer bundled up and tucked in little sleeve nests. I dug these out and wiped off the 50+ years of grimy waxy copper oxide-y goo that lurked in the sleeves and which had coated the wires. I took two and ohm'd them. Yes, continuity. Maybe there is a spare winding or a different tap / ratio that I could use if I needed to. I tried getting continuity from all of them to the pair that feed in the primary. Nothing.

I really did not want to figure out re-wiring the transformer from these spare taps (there are in total around 12 wires going in and out of it) nor did I really want to remove it from its mounting in search of part numbers (I reasoned that Anko had used an off-the-shelf transformer hence the spare wires) out of fear of tugging on and snapping some of the other fine (sometimes single stranded) enameled copper wires.

Instead I chose to check everything one last time, trace the wires from the mains lead to the input again, check connections, test individual wires from the tagboard to transformer by scraping back a bit of varnish and buzzing out.

Everything as I had first found. So let me just check that I was checking resistance on the correct pair. Back to the same terminals again. Oh...we have 18 ohms.

What had I done to 'fix' the transformer??!!

I double checked. Yes, now the primary had continuity. I applied power (120V, lamp limited), and was rewarded with a glowing diamond-shaped light and a meter steadily rising!

Whilst it was powered I gave it a few hefty blows to see if the temperamental 'whatever' would cause loss of continuity again but it took them with aplomb.

Everything looked (and sounded, and smelled) under control after 10 minutes so I un-limited the juice and let it soak for another 10 minutes under a watchful eye (and[listenful?] ear and [smellful?] nose!).


And now to cut a long story short before you all fall asleep... I:

1. Tested a 6V6. No result (well, the meter went backwards as it does when you are testing a valve element that does not exist - there are 4 'section test' levers you see). Wondered if there was another setting. The 'cap' (anode / 'plate') selector switch has four positions - P, X, G and C. The settings chart that came stapled inside the lid only mentions three of these. G gets no mention. Maybe that is the default for anode on the base pins rather than the top. Turns out it is as the 6V6 now shows life on the meter.

I tested a few 6V6s to get to grips with it and check for how it reports back on tubes of different origin, age and abuse. I also checked the heater pin voltages (OK) and learned that when the line calibration is set at the marker on the meter, putting a valve in causes that to dip a bit. I guess this is the load taken on by the filaments. By the way, unloaded a setting for a 6.3V heater was around 7V, so I suppose it makes sense for the dip on the meter. I haven't checked the voltage to the heater pins under load though. I suppose a manual would tell me all these tell-tale signs but as there isn't on available I'll have to surmise.

2. Screwed a 50VA 240->110 isolation transformer into the (now empty) suitcase. Plenty of room round the sides as the bulk of the workings are in the middle and the left and right sides are just low-profile sockets.

3. Made a note of which are the 'spare' sockets for wiring yourself to add extra support; as mentioned in the one advertisement for an Anko TeleTest that I have found. They are: 1, 23, 30, 52, 61, 65 and 72. Again, the manual would tell you that!

4. Had to repair two of the 'TEST' lever switches as during cleaning I discovered the bakelite posts inside had broken in the past and the previous owner shored them up with bits from broken valves! My solution was Sky Plast (a two component cross-linking non-toxic rubber compound) and Gorilla foaming glue.

5. Learned that the rotary selector switch shafts do not have flats so without making sure there is a witness mark from the grubscrew, you can't see which way round to put the chickenhead knob.

6. Tested a few multi section valves to confirm that the other 'TEST' levers work

7. Treated ALL the sockets with contact cleaner. There must be a special place in hell for massive tasks like this!! - but in all it only took 10 minutes.

8. Am going to keep this topic updated with more photos and details to help others out there who have acquired one of these units but are stumped on how to use or repair it.
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Old 30th Dec 2019, 2:24 am   #2
usradcoll1
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Default Re: Anko T72 'tube' tester - loadsasockets!

It's a small world, isn't it!
A friend had one. The unit was built in Milwaukee, Wisconsin USA by a concern that built tube testers for self service, called U-Test-Um. They were placed in drug stores, hardware stores, ETC. The tester you have was made for the servicing trade and is a little more accurate than a simple emission tester.
A little dated but I think you'll get a lot of use from it!
Regards, Dave USradcoll1
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Old 30th Dec 2019, 7:25 am   #3
Diabolical Artificer
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Default Re: Anko T72 'tube' tester - loadsasockets!

Nice work. You must have big suitcases, what's next a Tektronix 500 series curve tracer? Try sneaking that on the plane and through customs : )

Andy.
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Old 30th Dec 2019, 10:08 am   #4
donutty
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Default Re: Anko T72 'tube' tester - loadsasockets!

Yes Dave, they seemed to have passed through quite a number of people's hands but it seems nobody ever thought to photocopy or scan the manual. I don't suppose it is that complicated that it really needs more than a slip of paper but there are certain nuances as described above which would benefit from being formally explained by the manufacturer.

Andy - I fly Premium Economy or Business so you get more than one piece of luggage so I normally take an extra empty case. Sometimes it comes back full of records, sometimes radios, sometimes cameras or telephones! Funnily I have never been stopped by customs as I always declare what is in there before putting my bags through. I try and take the fragile stuff as hand luggage; and my items get a free internal inspection... in the form of an x-ray!

The Anko tester actually went as a self-contained item of luggage. It survived remarkably well and the only damage was caused by myself strapping the lid closed with gaffer tape. When removed it peeled off the surface layer of yellow lacquer. I hope some solvent and a brush will be able to blend in the existing stuff to restore the surface.
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Old 31st Dec 2019, 2:38 pm   #5
donutty
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Default Re: Anko T72 'tube' tester - loadsasockets!

A few more pics
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Old 31st Dec 2019, 2:41 pm   #6
donutty
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Default Re: Anko T72 'tube' tester - loadsasockets!

And a few more.

After I am back home after new year I will measure the voltages on each setting and whatever other unpublished details that I can.
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Old 31st Dec 2019, 2:53 pm   #7
Uncle Bulgaria
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Default Re: Anko T72 'tube' tester - loadsasockets!

What a beast! Are the different sockets all for different models of valves? Do the more modern testers with fewer sockets have some way of self-regulating for different valves that this doesn't?
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Old 31st Dec 2019, 3:48 pm   #8
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Default Re: Anko T72 'tube' tester - loadsasockets!

Quote:
Originally Posted by Uncle Bulgaria View Post
What a beast! Are the different sockets all for different models of valves? Do the more modern testers with fewer sockets have some way of self-regulating for different valves that this doesn't?
All those valve sockets saves a load of switching circuitry, amongst others the original Avo two panel valve tester was similar.

Lawrence.
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Old 31st Dec 2019, 8:24 pm   #9
usradcoll1
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Default Re: Anko T72 'tube' tester - loadsasockets!

Quote:
Originally Posted by ms660 View Post
Quote:
Originally Posted by Uncle Bulgaria View Post
What a beast! Are the different sockets all for different models of valves? Do the more modern testers with fewer sockets have some way of self-regulating for different valves that this doesn't?
All those valve sockets saves a load of switching circuitry, amongst others the original Avo two panel valve tester was similar.

Lawrence.
That model my friend had was slightly different, it didn't have the lever selector switches. It just had a single lever switch for shorts-gas and emission.
The multi-socket checkers were popular with the service trade for speed of setup. My B&K Dynascan 707 has multiple sockets, each covering most popular valves of the day. It is a true mutual conductance checker.
Like most of the newer checkers it doesn't check UX base valves. For that I have a government surplus Hickok design checker.
Dave USradcoll1 best regards!
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