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Taylor 45a valve tester

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Taylor 45a valve tester

Post by Sparks » Sun Feb 21, 2016 7:49 pm

Having just missed out on geting one on Ebay, I found a plan of one online, just out of curiosity. The heart of the thing seems to be the two transformers that are both very specialised. Apart from them, there is very little in it beyond the switches and valveholders. Outside the rectifier circuits there are only 3 capacitors, 11 resistors, one pot, and one rheostat! I had always imagined that they were complicated pieces of kit that could tell one everything one wanted to know about the valve on test! Exactly what sort of a tale do they tell of the valve on test? The one I missed went for just over £300, which would have been about my limit even if I had had sufficent time to get another bid in before it closed. After seeing the circuit, I am less keen to look for another!
Any reviews of this, or other types?
Bob

 
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Re: Taylor 45a valve tester

Post by Ed Dinning » Sun Feb 21, 2016 9:20 pm

Hi Sparks, yes the transformers are very complex, not only do they provide a multitude of heater voltages they also provide bias and electrode supplies. I have rewound a couple of these and it is no picnic!
Have a look at the handbook and it should be possible to make a simplified version if you only want to test a limited range of valves, alternatively go for the Sussex tester.

Ed

 
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Re: Taylor 45a valve tester

Post by Sparks » Sun Feb 21, 2016 10:28 pm

Hi Ed,
Thanks. My home-made one shown here on VRAT: http://www.forum.radios-tv.co.uk/viewtopic.php?f=15&t=12212&p=127585&hilit=valve+tester#p127585 works very well. I can get any heater Volts I require from a Variac feeding through an isolation transformer. HT from either a battery or another Variac with a DC isolated PSU on the end of it. I can even estimate the emmission by comparing a known good valve with an unknown. Just fancied a real tester, but it seems they always go for hundreds. I am going to build the Dynamic Mutual Conductance tester that we talked about yesterday. Sent for the capacitors & resistors today. I will have to use preferred value capacitors, but the resistors, I can make up from series/parallel connection. I suppose .47uF will be OK instead of 0.5uF.
Bob

 
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Re: Taylor 45a valve tester

Post by hamid_1 » Mon Feb 22, 2016 12:26 am

Valve testers do seem to be highly prized and can be very expensive as you've found out. I never considered getting one myself but last year I finally became the owner of a valve tester when I visited my cousin in Canada who has an electronics shop over there. In the back of the shop there was a valve tester which had been left behind by a retired engineer, and my cousin said "If it's any good to you, take it!" The offer was too good to refuse!

The valve tester was an EMC model 213 made by Electronic Measurements Corporation, New York, USA. Pictures of it here: http://www.radiomuseum.org/r/electroni2_tube_tester_emc_213.html The unit is very small, lunch-box size, just like those battery valve portable radios from the 1950s. It has a number of different valve sockets, a row of switches with neon lamps and a meter which reads emission (indicated by GOOD or REPLACE on a scale). The neon lamps indicate inter-electrode short circuits. To use the tester you must first look up the valve to be tested in the user manual, then set the switches on the tester accordingly. Testing is a two-stage process. The user manual says to carry out the short-circuit test first, and reject a shorted valve without further testing, otherwise the tester could be damaged during the next step, which is the emission test. Some valves have multiple sections, e.g. ECC83 is a double triode. In that case the emission test has to be repeated for each section.

It turns out that these basic testers were quite common in the USA and are not so expensive to buy, either. I used my EMC 213 to test a couple of new old stock valves as well as a couple of faulty valves which I had already replaced. In both cases, the tester gave a valid result, "GOOD" for the new valves and "REPLACE" for the faulty ones. I think the tester would be useful to confirm your suspicion about a valve during fault-finding. It would also be useful if you have a pile of old valves pulled from scrapped radios and televisions, and you wanted to know if the valves were likely to be serviceable or not.

The main snag with the American valve tester is that the handbook lists the valves by their American type number. For British valves I first have to find the American equivalent elsewhere, then follow the instructions for testing. Unfortunately some British valves seem to have no equivalents in the USA. If a valve is not listed in the tester's handbook, there is no way to test it. Without first applying the settings given in the manual which are unique to each valve, the meter reading is meaningless. Likewise, if you find one of those valve testers going cheap but without the manual, it will be practically useless unless you can get a copy of the operator's manual from somewhere. Luckily my tester came with an original manual, plus I found an updated copy on the Internet which allows the tester to check even more valve types.

The manual to my tester is here : http://bama.edebris.com/manuals/emc/213-215 - link at bottom of page. The manual includes a schematic diagram. It doesn't look very complex so it should be possible to build your own copy of the tester ... but you'll need a meter with the same characteristics as the original one, or the GOOD/REPLACE result will be invalid.

I'm happy with my basic valve tester (after all, it was a free gift!) though if you want something more than just a GOOD / REPLACE indicator, expect to pay more money. But before handing over hundreds of pounds for a vintage Taylor 45 or something similar, bear in mind that it's going to be at least 50 years old and may be inaccurate or faulty. There's a buyer's guide on ebay itself http://www.ebay.co.uk/gds/Choosing-a-Valve-or-Tube-tester-from-AVO-to-B-K-etc-/10000000007494378/g.html

If you have the time and patience, I reckon you will be better off building your own tester instead of buying an expensive vintage one.

 
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Re: Taylor 45a valve tester

Post by Sparks » Mon Feb 22, 2016 9:05 am

Hamid,
Thanks very much for the comprehensive reply that I have found to be very clear, and most useful. I have downloaded the circuit of your tester, and it is, indeed, even simpler than the Taylor 45a. I feel sure I can now work something out for a home-made version. My variac can be used in the place of a tapped transformer, so really, you have answered my question 100%, thanks again.
Bob

 
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Re: Taylor 45a valve tester

Post by Ed Dinning » Mon Feb 22, 2016 8:25 pm

Hi Bob, nearest value caps should be fine (.47 for .5; .22 for .25 etc). It may only matter if they are using different values in series as in AC bridge arms, but I doubt if your valve tester goes in to that sort of circuitry.

Ed

 
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Re: Taylor 45a valve tester

Post by Sparks » Mon Feb 22, 2016 10:15 pm

Thanks Ed, I though as much. The capacitors and pot are on their way. I may even find some of the correct value capacitors lying around, as I have so many of them. Resistors not much problem. I will make the 975 ohm resistor by having a 500 Ohm resistor in series with a 500 Ohm pot, and adjust it to 975! Very strange value though! I will use my sig. gen. for the 4 Khz input
Bob

 
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Re: Taylor 45a valve tester

Post by Terrykc » Mon Feb 22, 2016 10:32 pm

It is important to remember that capacitor tolerances have improved considerably over the years.

At one time, only values following a 1, 2, 5 sequence were available but these days the E6 series: 1.0, 1.5, 2.2, 3.3, 4.7, 6.8 are common.*

A modern 0.47µF capacitor will be well within the tolerance range of an old 0.5µF one and may well be closer to 0.5µF than a capacitor marked with that value!

* This is not a new process but simply follows the development path of resistors, where it was much easier to control production tolerances or, possibly, just the post manufacture selection process.

As a result the E6 series appeared very early on, being successively followed by the E12 and E24 series as tolerances continued to improve.

That is by no means the end of it - it is unlikely that anybody carrying out vintage restoration and repair will ever need anything other than E12 values - but, where very high tolerance values are required, additional value sequences up to E96 (and beyond) can be found.

See http://www.forum.radios-tv.co.uk/viewtopic.php?f=15&t=2344 for more detail including graphical details of how the values in each series mesh together to give a continuous sequence of values within each tolerance band.


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