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Are Valve tester's really worth it?

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PYE625
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I thought I would pose this question just for interest and to see what people think.

Without doubt, a CRT tester/rejuvenator is certainly of merit, but I often wonder whether a valve characteristic tester warrants the same merit.

Even though I own a Taylor 45D tester, it of course gives results of tests eg. mutual conductance etc, but over the years I have found the ultimate test of a valve is actually in the equipment where voltages and correct operation can soon be found.

For example, a low gain EF86 will of course have an output lower than a good one and the results easily seen in the reduced output in an amplifier that will not meet the manufactures spec.

Further, in a Quad II amplifier, a KT66 may have excessive grid current and go into thermal runaway. But when tested, the same valve will measure perfectly ok on the valve tester.

So, I do wonder how on earth a tester can possibly replicate every possible circuit configuration and test a valve in the same way it will be used in real life.

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Posted : 18/09/2016 1:58 pm
Nuvistor
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I never used a valve tester when I was in the trade, however I had always a stock of new valves. I always decided from the symptoms and measurements if I thought the valve was faulty and if any doubt I had new ones to try.

Probably not the same now with NOS and S/H valves that have to be used, a valve tester would give some confidence.

Frank

Frank

 
Posted : 18/09/2016 2:06 pm
Norman-Raeburn
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I also have a Taylor valve tester and rarely use it. As you said it is difficult to replicate the working conditions. The only time I really use it is when I suspect a valve as being faulty and don't have a replacement to try. This may save me from making expensive mistakes when the valve may not be faulty. I believe the biggest use is when people are selling valves and want them tested. Norman

 
Posted : 18/09/2016 2:08 pm
Cathovisor
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The short answer is - it can't. It can only tell you how a valve compares to its published data.

I've got an AVO VCM Mk. IV and it's useful for doing things like checking a boxful of random ex-equipment valves for awkward things like heater/cathode leakage and inter-electrode shorts (a friend of mine's just had an odd one where the signal diodes in a UBL21 seemed to be at HT!) and for putting said valves into your personal stock, but other than giving the hi-fi fraternity something to bill and coo over when checking their valves, an operational check is the best way.

There is a gentleman on this forum with whom I discovered said inter-electrode shorts inside an EB91 simply by looking at the voltage readings in the set it was in.

 
Posted : 18/09/2016 2:09 pm
crustytv
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For me I had no need for valve matching or other sophistication offered by the likes of AVO. A straight forward go-no-go with simple tests such as insulation, grid current, emission and other electrode short tests. No complicated set up either. For me the Mullard filled that requirement.  Also coupled with a stabilised voltage supply, essential otherwise readings will be meaningless.

Now I'm mainly solid state, it never gets an airing. Though recently a mate wanted a large batch of valves tested so he could sell them. With this I was able to state the emission level and if there were any electrode issues all very quickly. Just a case of looking up the card and pushing the buttons.

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Posted : 18/09/2016 2:26 pm
ntscuser
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Many years ago the father of a friend of mine died and left his TV repair shop to his widow. The only piece of test equipment in the shop that I could see was a valve tester. She seemed to manage with that and (possibly) a hand-held multimeter. This was before colour of course.

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Posted : 18/09/2016 2:35 pm
sideband
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I used to have a Taylor 45B and it was useful for testing unknown valves acquired over many years. At least it could give a good indication of emission and general 'goodness' of a valve. After testing around 100 valves, I had no further use for it and sold it on eBay, the money I got for it funded several radio's and a TV purchase.

 
Posted : 18/09/2016 3:10 pm
Brian Cuff
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In the 1960s. I used to work in Telecine at the BBC. The machines were all Cintel valved examples each with at least 50 valves. One of the worst jobs to do was a routine valve check where during a maintenance day, every valve in the machine was tested using an AVO MKVI tester. If the valve was under 70% emission/gm, it was changed and dumped. The replacements weren't tested as they had the BBC Valve Section green labels saying it had already been tested. Fancy testing every valve which came into the BBC in the days when there wasn't any solid state stuff!

No, I don't like valve testers and I use my MKVI on a very intermittent basis - I seem to have a bit of a phobia about it!

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Posted : 18/09/2016 5:07 pm
TVJON74
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I have an AVO CT160, it has sat on the bench for quite a number of years (probably since I purchased it) and I have only used it a hand full of times. Even then I'm not too sure I'm using it correctly, I much preferred my MK4, but when times were hard I had to sell it.

I must fire it up at some point and practice using it, as I have quite a number of valves in an unknown condition. I guess like most things they have there uses.

Jon
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Posted : 19/09/2016 4:49 pm
Katie Bush
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A valve tester is something I aspire to, one day, but I doubt it will happen any time soon - I have acquired a heap or two of used valves in unknown condition, even so, there are more useful items that will most likely come first.

 
Posted : 19/09/2016 8:51 pm
frankmcvey
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Valve testers have their place.  As another poster has observed, the best test for a valve is by doing voltage and current checks in the circuit in which it is used.  However, you need some knowledge for that, and sometimes circumstances arise where it isn't practical or possible to do that.  

I have a Taylor 45C, a couple of American go/no-go emission testers and 11 Mullard High Speed Valve Testers.  3 of the last-named are serviceable -  the rest are in the process of restoration or are on the to-do pile.  I love HSVTs - a real elegant bit of kit for the work it does.

The Yanks see no use at all.  They're fine at what they do, but they're limited.  One of these days, I'll sell them on.

The Taylor is a very nice machine and comes in handy on the very few occasions that I have to match valves.  

The HSVTs, like their name implies, are great at working their way through a large bread-tray-full of valves quickly, giving a definite good or bad, plus an amber "OK at the minute, but you'll need to change me soon".  Plus they're pretty bullet-proof for a novice.  There's no very expensive meter to wrap around the stops if you screw up your switch settings - the spot simply flies off the screen, or the reset relay trips.

If you have a large stock of known serviceable valves, like the old-school engineers, then you can simply substitute a valve if you have a snag.  If you don't have access to a huge range of serviceable valves, then a valve tester is another useful tool in your toolbox. 

If you grade your test kit into the categories: Essential, Important , or Desirable, then I'd put the valve tester at the Desirable end of the scale.  Most of the time you don't need one.  But when you do, they're a great bit of kit to have.

Cheers,

Frank

 
Posted : 30/11/2016 1:23 am
Anonymous
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Hi

I was wondering if anyone is still messing around with the AVO 2 panel valve tester.

I've just got the naval version and looking at the circuit it looks as though the meter can't be backed off to zero 

in neutral like the "non naval tester" as the anode feed via the "rst" switch does not go

anywhere. It only connects when the switch is in Ma/v 

Anyone care to comment.

Regards harry

 
Posted : 31/07/2018 7:01 pm
Nuvistor
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I never had a valve tester, but has frankmcvey notes we always had a stock of new valves if there was any doubt about the quality of the valve. In circuit tests with a meter etc in many cases will show what state the valve is in.

Some valves are not easy or possible to test such as line output, boost diodes and EHT rectifiers, they may show good but break down with the high voltages in circuit and not available on the tester.

However, always a but, if you have a number of valves of unknown condition a valve tester at least will sort them out into bad, maybe and good.

So it all depends on what you need.

 

Frank

 
Posted : 31/07/2018 7:19 pm
crustytv
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Hi Harry,

first of all a warm welcome to the forum  ? 

Many years ago I had the AVO two panel valve tester (see below) not the naval version though, so cannot comment. I sold my AVO and moved to a Mullard MKIII which was more suited to my needs.

It would seem odd if you cannot back the meter off via "set zero". However not to worry I believe one of our members @freya (Stephen) does have the same naval version as you so maybe he will be able to offer you some advice.

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Posted : 31/07/2018 7:44 pm
Cathovisor
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Just out of curiosity, is @scommstech actually referring to the CT160 rather than the one above?

 
Posted : 31/07/2018 7:49 pm
Anonymous
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Hi Chris

I also have an ordinary 2 valve tester and in that one you set the meter zero with the Ma/v ins switch in the neutral then push the switch over to the Ma/v to take a measurement, either good or bad, or read off the currant for a Ma/v reading. the "PO" toggle switch seems designed for that sequence. First zero the meter then take a reading.

The naval tester is using a 2 coil solenoid over load cut out for the anode circuit and the screen circuits, either one will trip. Why they did not just "cut" into the existing wiring beats me. They have chosen to utilised a disused section of the "PO" (RST) but in the neutral position it does not connect to the meter circuit so according to the diagram there is no way to zero the meter.

Harry

 
Posted : 31/07/2018 9:30 pm
Anonymous
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Hi Cathovisor

I was referring to the 2 panel AVO (may be called the MK1). It is the naval version that looks identical to the basic model apart from a red lens in the top right section of the dial. The naval version includes cut out solenoids.

Regards

Harry

 
Posted : 31/07/2018 9:36 pm
raditechman
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We had a Mullard "Hugh Speed" valve tester in the workshop at one place I worked,  it was seldom used.

I think the main use of the testers was in small independant shops that could offer a valve testing service for say half a crown and then possibly  sell you a new valve for 15 shillings afterwards!

John

 
Posted : 01/08/2018 7:44 am
Nuvistor
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Valve testers used in small shops is a possibility but I never saw that.

 

Reading USA magazines the use of valve testers in the local Drug Store was common, customers would test their own valves and purchase what was required. Seems many would have all the valves out of the TV and test them, I wonder with some how many valves went back in the correct socket.

Lots of hand wringing by TV repair shops as to whether they should provide a tester for the public to use.

 

Frank

 
Posted : 01/08/2018 9:04 am
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