Choosing a Valve or Tube tester from AVO to B&K etc

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So you are thinking of buying a valve (or tube) tester and perhaps wondering where to start.

What to avoid - things that look like valve testers

1)The  type of tester you want to avoid are "utility testers" that just check filament continuity – you can do that with a multi-meter. These are worthless but as they have valve bases on them and a meter that is used for checking voltage and continuity you can be mislead. 

2)Another possibility is there are also some testers that only test "CRT Cathode Ray Tubes "that look like valve testers and both Sencore and B&K made them. A CRT tester will not test valves but some valve testers did come with adaptors to test CRT's. The give away here is there are no sockets on a CRT tester just a lead with various adaptors that plug on to the end.

3) In the mid 1930's "set analysers" appeared on the scene. They look like valve testers and were used by removing a valve from a radio set, plugging the valve into the analyser then plugging a lead from the analyser into the radio. You could then measure voltages and currents in the radio. By the mid 1940's they had evolved to do limited testing on those early valves as well but then proper valve testers appeared on the scene in the 1950's and set analysers died out overnight. They can look good having several meters but are very limited in todays world.

What to buy:


First on the food chain are the emission testers and most of these testers produce very credible results yet remain light and portable and very easy to use and read. Most of these testers will indicate internal shorts, gassiness and give you a quality or strength reading that allow you to grade your valves. By watching the speed of response of the tester you can get a feel for the life left in a valve. Interestingly the only valve tester made by Mullard was an emissions tester.


If you are willing to spend more the best testers are mutual conductance testers but these are rarely truly portable and in the case of AVO machines definitely not portable and require some study of the manual before you can use them.

 

Setting Data is vital:


When buying a tester you must get the valve setting data with it or know where you can get the data from – you wouldn’t buy a computer without any software would you?  The question you need to ask  with valve data is if the copy you are supplied is up to date.  For instance B&K data tables have the date in code on the bottom left so 1273 would be telling you this was Dec 1973 issue of the data. Manufacturers issued 6 monthly or yearly updates and corrections in the 60’s and 70’s and if your booklet is dated 0665 you can be sure there are a lot of settings missing and some might be incorrect.

 

UK v USA approach


Most of the reasonably priced easy to use testers were made in the USA. The USA took the view that anyone should be able to plug a valve into a cheap tester and see easily if it was good or bad. The UK took the view that valve testing was something to be done in the laboratory by men in white coats and produced laboratory standard testers that will give you chapter and verse but you do need to concentrate when using them.  The USA ones are 110 to 120v testers. This is no problem as a step down transformer bridges the gap.

The Makers:

Sencore made solidly built emission testers called  "mighty mite"  starting with TC109 or Mk1 this was superseded by the  Mk2 then  3 4 5 6 up to the TC162 or MK7. Up to Mk5 they were all valve based testers and the main difference was the addition of extra sockets to check 10 and 12 pin valves. All mighty mites had a very good grid  leakage test that reads on the meter. The later testers namely TC154 Mk6 and TC162 Mk7 went for a solid state FET circuit instead of a valve powered circuit. Sencore claimed the advantage was "instant on" but I think the advantage was all theirs in reduced manufacturing costs. As you have to wait for the valve under test to warm up i think*instant on "  is a pretty useless advantage and it came with a disadvantage - namely the FET circuit seemed less forgiving of operator mistakes and then is more difficult to trouble shoot and repair as you have to try to source the solid state parts.  

EICO had the similar looking 625 and 628 that were both heavy construction large testers in steel cases with big meters. Both have a wide range of valve testing data available and particularly useful are the supplementary charts that update and correct the built in roll of valve data as the very early 625 rolls had errors. The 625 has sockets and data for the oldies from 4 pin up to 9 pin miniatures like ECC83 whereas the slightly newer 628 omitted the earlier 4 5 and 6 pin sockets but added the 10 pin miniature and compactron sockets of the very last valves. The 635 followed and was a simpler machine that no longer had the line voltage control or overload indication of the earlier machines, was of lighter construction and was mounted in a plastic case - none of which could be consider improvements over the earlier models.

Heath, Paco, Triplett, Knight

Heath made a range of test equipment including large testers with good sized quality components. The first range was named the TC then later the  IT range. Several manufacturers at this time gave you the option of self assembly to reduce costs and these could be supplied as kits for you to build yourself or fully assembled from the factory. There are collectors of the Heath range of equipment and I can understand why there is a following for these solidly specified testers

PACO also made the same type of tester as the above with almost identical circuit in their T60 and similar remarks apply as with Heath above and Knight below.

Triplett made the 3413 tester with a similar circuit but heavier better quality components as the Heath, Paco and Knight and there is some interchange of valve setting data between these products.  

Knight had a similar range to Heaths TC range called the 600 range that were similar in size and range of valve checked and are good sturdy jobs, Towards the end of the golden age of valves Knight produced the 400 series of machines. Although the 400 and 400A look similar the 400A added extra sockets and the detailed set up data is also very different so do not try to use 400 set up data with a 400A or vice versa.

Radio City Products (also known as RCP) made a brief appearance in the 1950's with the 300 series testers. The best feature was the solid wood boxes they were in, the worst feature is they were not around for too long and the valve data available for these testers is limited to older valve sand even then is not very comprehensive

B&K made a good quality emission tester in the 600 range with a strong gas test.. The 600 then the 606 are very similar and good sturdy machines. These were replaced by the 607 and the 667 and the later ones were solid state but unlike the solid state sencores seem to be zap resistant with adequate transformers. The 625 was a 600 with VOM and CRT test facilities built in. 

B&K also made a range of mutual conductance testers all of which were good but none great as they all have weak spots. 

The 500 was flawed as it tested both parts of valves like ECC83 at the same time and  added the results together to give one reading so you are unable to tell if the valve is balanced. 

The 650 has a limited range of valve settings. 

The 700 and the 707 both have quirks. They are effectively two testers in one. The upper half of the tester does a Dynamic Conductance test and the lower half just tests for emissions and you do not get to choose where the valve goes and lots of common valves like an ECC88 for instance are tested on the lower part so you can only do an emission test. The other oddity on 700 and 707 as against other Dynamic Conductance testers is the meter is scaled 0 to 120 which does not relate to anything else neither manufacturers data or other testers.  The 707 was the same as 700 but replaced the plated steel panel with an aluminum front panel. This panel corroded and gave earthing problems so you are better with the 700 model. Their last gasp was the 747 which was a very good mutual conductance tester in a rather nasty plastic case that the hinges snap off and horrible switch gear. If you can get past the case and switch gear it is a very competent tester indeed suited best to those who do not need to test the older valves.

A good general point is raised here that both B&K and Sencore switched from the robust rotary wafer switches with chicken head or similar type sturdy knobs to rather flimsy slide switches or push switches with push on plastic knobs and these have not stood the test of time well.

Superior were another maker with a large range of models. They were in the market early and there first offerings were in lovely oak dovetail jointed cases. The TV10 and TV11 were in the oak case and look stunning. The performance on the valve quality test of these two was mediocre though  Full marks to the makers for wanting to adjust the mains voltage but this was a weak point  as it was asked to dissipate large quantities of heat at some settings and burnt out voltage controls on these early models is not unknown. Later models dispensed with this control with some having a switch for high or low voltage settings and some having nothing.  A good later model was the TW11 which was still in the oak case but was much improved. They also produced lighter smaller models such as the TC55 and TD55 which were very compact and ideal for taking with you if you get out and about testing equipment and had a high low volts switch. The model 82 is best avoided as it is inflexible so very limited in what you can test on it. They corrected this inflexibility with the model 85 which is a  tester that produces excellent results and is very flexible.

Sylvania were prolific USA makers of valves and they also made a range of professional quality testers to check out all makes of valves. As would befit a manufacturer of valves the build quality of these machines is exceptional with large heavy transformers, precision wire would resistors, heavy steel cabinets and lovely quality switches. They were however a little more complicated to use but this reflected the detail of the tests they could carry out. Models 90 and 140 are limited in the range of valve setting data available but the 220 model has a much better range of valve data available. 

Precision made some very good older testers with their "electronamic" testing system which is  a dynamic test system. The large 910 (small meter) 912 (larger meter)  920 (volt and resistance measuring) and 954(more sensitive meter) Mainly in large nice quality solid wooden boxes - those with with built in amps volt ohms testers see previous comments about built in amps volts ohms as it is easy to zap a meter measuring volts on the resistance scale - result no valve tester either so be careful if using the ancillary functions.  Only the later ones from the factory had a B9a socket fitted as standard although an adaptor can be used.. The follow up to the 900 series was the 600 series and 10-series  machines.

Accurate had three models the 151, 157 and the 257. They were also sold under the Lafayette label in Japan. These were good compact testers and very easy to use with large meters. The 157 is able to test the newer 10 and 12 pin valves otherwise there is little difference to the 151. The addition of the extra sockets took away the cable storage area that is present on the 151 so you do need to be a little careful when closing a 157 to ensure the plug doesnt get trapped by the lid and crack the perspex meter cover. The 257 added the ability to test CRT's  (tv picture tubes), a, a larger meter that is easier to read and an easier shorts test that is carried out automatically during set up. 

Taylor were a British maker of testers with similar thinking to the AVO range in they used a back off system to check valves so they are not the easiest to use. In later years they were bought by the same company that owned AVO and this showed in the 45D which had an AVO influenced and improved standard of construction over the previous 45 models. All the model 45 range will do a good mutual conductance test. The 45A is the oldest and would not have left the factory with a B9a socket (think ECC81 etc) and sometimes suffers from burnt out resistors. The 45B replaced the A and added a gas test as well as the B9A socket. Next to come out and replace the 45B was the 45C that went from 9 switch positions on the A B and C to 17 positions on each selector switch positions and that increased the flexibility and number of valves it was able to test over the A and B variants. The 47A was a 45A with an additional panel to read volts and ohms and the 46A was a 45A able to read plate currents.

The 45D will do all the above and more. The abandoning of the 3 switch selector system of the A B and C models  and the addition of a 12 way AVO type wheel selector opened up testing of the newer valves with more than 9 pins. The 45D will also have a stab at anode current as well which the earlier ones do not. . These 45Ds can be considered as a more affordable alternative to the AVO range of testers and as they are modern by tester standards have very comprehensive valve data available and newer components used in the construction..

 

What to look out for when buying

If you see a tester for sale that has suffered by being stored in damp conditions and exhibiting a musty smell you are advised to steer clear as the dampness will have taken a toll of all the contacts and connections. If you see a tester with its mounting screws missing – steer clear as the previous owner didn’t even think it was worthwhile putting it back together after trying to fix the fault. If you see a tester with the plug missing – does this mean the previous owner thought the plug was the most valuable part of the tester or was it just so dangerous that he didn’t want anyone pluging it in. If you see a tester and cannot see the meter move this is a bad sign -  a dead or burnt out meter means the tester is probably worthless as your chances of finding a replacement are small.  A lot of testers are described as “untested but powers up” or “light comes on” but as many testers do not have a mains on lamp and the only light is the the shorts light and this should only light when a shorted valve is tested “light comes on “ when first plugged in can be a bad sign. As for “powers up” a valve tester does nothing until it is set up and a valve is fitted so all this is telling you is the fuse is good and it didnt burst into flames.  By and large testers are remarkable reliable and although most are 40 years old plus they are still in working order - wether they are accurate is another question of course. There is a saying "A man with one tester can tell you the performance figures for his valves - a man with two testers is unsure" and this is because it is rare to find two testers that will agree 100% with each other. This is not to devalue testers but there are so many variables and test conditions that when you see someone selling a budget tester and saying it "agrees 100% with my Hickok or Avo or Weston or Amplitrex " or other mega buck high end tester you should take it with a big pinch of salt and also question everything else he has said in the blurb..

You will see some testers that have a lot of sockets all the same size (say 15 off  B9A 10 off B7 and 8 octal etc)  and only two control knobs. Your first thought is that this type must test lots of valves as there are lots of sockets but this is incorrect (unless it a  B&k700 or 707) as the range is limited and there is no flexibility. You will be better with a tester that has only say two or three sockets of each type but with 

a) three or four set up knobs and no levers or 

b)two (or more) knobs and a series of 10 (or more) switches or levers -

there is great flexibilty with either of these arrangements.

Mullard made exceptional valves and also marketed a valve tester. This used cards to set the tester up. You need a specific card for each type of valve you wanted to test. The beauty of the system is you need absolutlely no knowledge at all and once the correct card had been put in the tester anyone could test 100's of that type of valve very quickly. The disadvantages however are several - if you do not have the card you cannot test that type of valve, the tester and its chests of cards are very large and heavy and probably worst of all the tester has no meter to give a reading only a magic eye. The quality of the valve is seen as a dot on the magic eye and the higher up the magic eye the dot is the better the valve - to my mind anything that is measuring should have a meter to quantify the result. What amazes me is that for its size, weight and complexity this tester only measures emmissions not mutual conductance. Food for thought though that a company like Mullard believed emmissions testing was good enough for them to accept and reject valves.  

The AVO valve testers are worth a few comments on the individual models. The first is the two panel tester and these are good for older valves but have no sockets for the 7 pin and 9 pin miniatures valves like ECC83 or EL91. You can make adaptors or fit sockets to the panel and wire them in to overcome this problem . The testers are relatively simple in construction,  reliable and will measure mutual conductance and indicate but not quantify plate or anode current. They are limited to a maximum filament voltage of 40 volts, and the anode and screen voltage is limited to 250v and as a result the set up data is very different to the more sophisticated machines that followed.

Next from AVO comes the VCM's (valve characteristic meters) . MK1 VCM and the MK2 (like a MK1 with the addition of two small cupboard type handles on the front and a storage tray underneath) these both had a one piece lift on cover . The Mk3 and Mk4 are also similar in appearance having removeable end covers and large curved handles from top back to bottom front. They also made the CT160 which is  in a clamshell case and was used by the military. All these are complicated pieces of equipment which require study before use and calibration if they are to give reliable results. They will all measure mutual conductance and plate or anode current and will check most valves you are likely to want to check. My previous comment on meters applies double fold with any of these. The meters were very sensitive and easy to burn out. This is partially due to the way you use them by using backing off controls each time you check a valve. The temptation is to forget to zero the backing of controls after checking the last valve or forget to reset the meter range after checking the last valve then when you put in the next valve - zap - you have a problem - a burnt out meter. There is some protection built in but it often cannot react quickly enough. Users who only use this type of tester rarely are most prone to this as you forget the sequence from the last time you used it. There are NO meters available from other meter makers that you can buy and substitute that will allow a direct swop - this meter was peculiar to AVO. The other mode of failure of the meter was corrosion of the metal parts of the meter which resulted in the moving coil of fine wire having insufficient room to swing round freely so the meter became sticky at points on the scale. The temptation is to carry on using the tester giving the meter a tap to free it off but eventually the coil becomes damaged and the meter dies. The MK1 and Mk2 meter although looking the same externally as the ones fitted to later machines are not interchageable electrically with that fitted to the MK3, 4 and CT160. . If you buy any of these testers without seeing the meter move freely throughout the entire scale before handing over the money you are taking a big gamble as this is a common problem and burnt out meters was the reason why a lot of these testers ended up in lofts 20 years ago or in the case of moving but corroded sticky meters are destined for a short life. You can almost guarantee if you see the words "untested" in the sale details for an AVO it will not work.  The other common fault with them is burnt out or partially damaged back off control potentiometers and this only comes to light when you start testing valves. Again some of these were specially made wire wound pots for AVO with special characterisitcs so good luck if you need to replace one of those.

 Lastly AVO produced the VCM163 which had two meters so you could read anode current and mutual conductance simultaneously. This tester also had more ways on the multicam set up switch thus making it even more versatile and sought after.

 

There are a lot of alternatives in the world of valve tester and it depends on your budget and what you want to do with a tester. I would suggest before you buy that  tester you talk to someone who has used a range of testers. Before you commit to buy something you are welcome to use ebays ask me a question and tell me what you want from a tester and I will be more than happy to make some suggestions as to  what you might best be looking at -  for free! I also offer free support by email to get you going if you have bought a tester from me .

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