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Old 28th Aug 2020, 1:18 pm   #1
aviv_zl
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Default New (to me) old Taylor 45D - where to start?

Hi everyone,

Yesterday I managed to acquire a Taylor 45D valve tester. I bought it from the owner, who bought it somewhere in the 70's. He says he purchased it directly from the importer, but he never used it and just kept it all the years. Generally it's in good cosmetic shape, but I can recognize some scoring marks near the side screws, so obviously someone opened it at some point of time.

Internally, it also looks quite clean. However I have found two potential issues:
1. On the wires of both transformers, there is a white-gray salt-like (bit sparkling) residue, not sure what it is. It is found only on the transformer wires. The rest of the wiring harnesses are clean.

2. Four of the rotating pin selector wheels will not rotate beyond a certain number. Few rotates up to 2, others up to 3. None of the wheels rotate beyond 6 (which is normal I guess). It feels like they hit some hard stop.

I didn't power it up yet, as I would not try to crank a ~50 years old machine w/o some basic checks.

I obtained the user manual, and with the valve data which was sent to me by a kind forum member.

Where to start?
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Old 28th Aug 2020, 3:55 pm   #2
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Default Re: New (to me) old Taylor 45D - where to start?

The stuff on the transformer wire insulation sleeves may be a fungus growing on the rubber in a hot climate. It shouldn't be a problem, but try removing it with a small dry brush if you're worried. With any such growth, you do not want to risk inhaling spores.

The Taylor 45D dates from after AVO bought Taylor and the roller switch is essentially based on the parts used to make the AVO one. DO NOT FORCE IT. You'll have to dismantle it, clean it and reassemble. Look for details in threads on the AVO VCM163 and you'll also see the instruction to only ever turn it in one direction.

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Old 28th Aug 2020, 7:31 pm   #3
David G4EBT
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Default Re: New (to me) old Taylor 45D - where to start?

That looks in very nice shape internally and externally and unmolested too.

I think as David says, that looks like just a bit of mildew which could be dusted off.

Early days yet, but if it transpires that any of the first nine roller switches are beyond repair, the last three to the right are rarely if ever used, so could maybe be swapped over.

You were quite lucky to obtain the valve data. I bought my 45D back in the early 1980s when valve-testers were largely considered unsaleable junk (yes, there was such a time!). It had been on the B&B stall at a radio rally all day unsold. It was an impulse buy and thought it was expensive at £25 and my offer of £20 was accepted. (Equal to about £70 today). I had to buy the valve data book from AVO which cost me £18.00.

A couple of points worth mentioning:

Firstly, I put a label on top of mine to remind me not to carry out a cathode leakage test on directly-heated cathode valves, especially delicate battery valves.

Secondly, depending on your interests, you may find it useful in due course to make some adaptors to extend the range of valves that you are able to test.

Originally adaptors were available as accessories but rarely turn up. I made six myself which I can plug into the I.O socket. (The original adaptors plugged into the B14E socket). All of the pins on valve holders of the 45D are 'commoned' so all pins 1,2,3, etc are connected from one holder to another. Hence, as long as the additional range of valves that you need to test have 8 pins or fewer, you can make adaptors to suit using I.O bases from donor valves (though new bases can be bought on eBay).

I posted a thread about that on the forum some time ago, but the pics below show the adaptors I made and how I wired them. I turned the plastic couplers on a metalworking lathe (I used the resistor colour code for wiring the pins).

Hope that's of interest and help.
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Old 29th Aug 2020, 5:24 am   #4
aviv_zl
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Default Re: New (to me) old Taylor 45D - where to start?

Thank you both for the information.

Yesterday I started the disassembly process. I have to say that this chassis design is not very friendly for servicing. There is no easy way to open it up completely w/o unsoldering completely both transformers, which is a pity. I took out all the selector cassette and disassembled it completely. Luckily nothing broken, they are all in a good shape and were stuck due to dry lubrication. Attached are some pictures-

Should I polish the slip surfaces of the selectors with a fine emery paper or they are coated and it’s better to leave them as is?

BTW, the selectors do have hard-stop pins which prevent going beyond #6. Therefore, they cannot revolve completely and must be turned back and forth in both directions.
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Old 29th Aug 2020, 1:14 pm   #5
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Default Re: New (to me) old Taylor 45D - where to start?

I wouldn't advise the use of emery paper. In most cases application of Servisol 10 will do the job. DeOxit is said to be better, but it's expensive. If the tarnishing is really bad try some Brasso applied with a cotton bud. Clean it off afterwards as it leaves a white deposit. I don't know whether these products are available in Israel.
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Old 29th Aug 2020, 5:18 pm   #6
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Default Re: New (to me) old Taylor 45D - where to start?

The tarnish is a dead give-away that there is some sort of silver alloy plating. It's self-lubricating as metal on metal contacts go and cleans up by wiping. Rotating the switches should show them to be self-cleaning.

I wouldn't use any abrasive.

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Old 30th Aug 2020, 10:08 am   #7
Craig Sawyers
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Default Re: New (to me) old Taylor 45D - where to start?

The black deposit on the switch parts is silver sulphide. And the silver plating will be thin.

But you can see clean contact area where the wiper has rotated. As David says, don't clean them. Any attempt to do so will reduce the thickness of the plating or remove it altogether - which will spoil your day big time.

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Old 5th Sep 2020, 8:52 am   #8
aviv_zl
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Default Re: New (to me) old Taylor 45D - where to start?

So finally all the selector wheels are cleaned and lubricates. I will upload some photos later on.

Next challenge- how to clean the tube socket pins? Is there some “magical tool” for that?

Cheers,
Aviv.
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Old 7th Sep 2020, 9:04 pm   #9
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Default Re: New (to me) old Taylor 45D - where to start?

Here is an image of the assembled selector unit. I added small bends between the wheels, before soldering, to relieve mechanical stress, which exist when then bus wires are straight.
What is interesting to see is that most of the wheels have hairline crack near #2 and #5. The reason for that is an internal stopper aluminium pins, which are riveted to the plastic wheel. However, it seems to have no significant effect on the selector.
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Old 7th Sep 2020, 9:19 pm   #10
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Default Re: New (to me) old Taylor 45D - where to start?

After cleaning and puting everything together, I turned on the tester for the first time and tried to test some valves. Filament and gm tests seems to work fine, with cathode leakage and anode current it seems to have some issues. I'm not fully sure. This is what I observed:

Cathode leakage-
The manual says "the meter pointer will kick to the right, then fall back to some steady reading". What I actualy see that the meter stays at zero (left) and slowly goes up to indicate the leakage. With two tubes I tested, the leakage indication shows 0.5M Ohm. When I hook DMM between the cathode and the heater of these tubes, the DMM could not measure any resistance. Is this a mistake in the manual or some issue with the tester?
I checked C3 which is a film capacitor of 0.1uF, I found it to be about 300nF. This capacitor seems to be used only for the cathode leakage test.

Anode current- when I set the tester to measure anode current, the meter will imediately goes up to about 1/8 of full scale (before depressing the test button). Is this a normal behaviour?
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Old 11th Sep 2020, 8:27 pm   #11
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Default Re: New (to me) old Taylor 45D - where to start?

When switched to cathode leakage, the meter will only start to move away from zero when the cathode heats up, so this takes several seconds. I would expect it to deflect to the right and then settle back to the leakage value shown on the scale. Most valves I have tested show leakage resistance of about 3 to 4 megohms, occasionally less - the worst I have ever found was 250 kohm.

On anode current, there will always be some reading on the meter, but the correct reading is with the test button depressed - read the anode current on the 10mA or 100mA scale as appropriate.

Hope that helps.

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Old 12th Sep 2020, 6:27 am   #12
aviv_zl
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Default Re: New (to me) old Taylor 45D - where to start?

Tahnks Roger. This really helps.

I copied relevant parts from the manual, where the cathode leakage test is explained with a simplified circuit. Could someone explain what is the purpose of C3 and how the tests works in more details?
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Old 19th Sep 2020, 12:12 pm   #13
aviv_zl
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Default Re: New (to me) old Taylor 45D - where to start?

for the sake of the future reader, I was finally able to track down the source for the false cathode leakage reading. With the help of kind members like Roger and David, I was able to determine the correct behavior of the cathode leakage tester.

There is a mistake in the manual- the meter does not kick to the right and then fall back to a steady reading. Instead, if there is a leakage, it slowly moves to the right to indicate the leakage resistance.

As I suspected, the problem was a leaky capacitor which is used in this test (C3). After replacing the capacitor, when testing a leakage-free tube, the meter does not move at all (indicating high resistance). When I added 0.5M or 0.1M resistors between the H+ and the cathode, after few seconds, the meter slowly moves to the right, indicating the simulated leakage current.
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Old 19th Sep 2020, 12:46 pm   #14
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Default Re: New (to me) old Taylor 45D - where to start?

The leakage test is powered by an AC voltage from the anode section of the power transformer, but the meter movement reads DC so all the electrodes of the valve are strapped to act as a rectifier with respect to the cathode.

The capacitors are used to route the AC voltage while keeping the leakage current separate, and to act as a pre-meter filter.

Part of the DC loop is through the transformer winding.

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