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

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, gasiness and give you a quality or strength reading that allow you to balance out your valves. By watching the speed of response of the tester you can get a feel for the life left in a valve.

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.

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.

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 BUT there are some of these 115v testers than can suffer swamping of their small internal transformers when matched with some stepdown transformers that push out voltages in the 120+ range.

Sencore made solidly built emmision testers called  "mighty mite"  starting with TC109 or Mk1 this was supersceeded by the  Mk2 then  3 4 5 6 up to the TC162 or MK7. The MK 1 or 109 is a little different to the following units and uses a different circuit and set up book. From TC114 or Mk2 up to the Mk5 the main difference was the addition of extra sockets to check 12 pin valves and then transistors as they all had similar circuits and used a common settings book (with the exception of the  Mk1). All these mighty mites had a good leakage test. 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 as you have to wait for the valve under test to warm up i think this is a pretty useless advantage and it came with some disadvantages - namely the FET circuit was more prone to being zapped by user error and is more difficult to trouble shoot and repair as you have to source the solid state parts whereas the old valve circuit you unplugged the 12AU7 and fitted a new one.

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 usefull are the supplementary charts that update and correct the built in roll of valve data as the very early 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 minature and compactron sockets of the very last valves..

Heath made large testers sold as Heathkit with good sized quality components mainly in the TC then the IT range. Some were supplied as kits for you to build yourself and some models were supplied fully assembled from the factory. If you buy a kit that was built by a dab hand with the soldering iron it will be every bit as good as a factory made job but you might buy one that was built by someone with limited skills. This might have dry joints or be wired up incorrectly and never worked properly from the day it was built so make sure you know it is working properly when you buy it.

PACO also made kit type testers and similar remarks apply as with Heath above.

Knight had a similar range to Heaths TC range called the 600 range that were similar in size and range of valve checked, Towards the end of the golden age of valves they added the 400 series of machines. Although the 400 and 400A look similar the 400A added extra sockets. The detailed set up data is also different so do not try to use 400 set up data with a 400A or vice versa. The meter seems to be a delicate item on these testers with burnt out meters common.

B&K made a good quality emmision 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 built in. The danger with this is you do some meter readings on the ohms scale then forget to switch to amps and do a current measurment and zap your meter which then means that as well as losing your VOM ranges you no longer have a working valve tester as well - me - i'll carry two meters.

B&K also made a range of mutual conductance testers. The 500 was flawed as it tested both parts of an 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 and the 650 has a limited range of valve settings. The 700 is a very good tester indeed with a wide range of settings and the ability to test individual parts of a valve and it is very quick to use. Note however that only the upper half of the machine is mutual conductance with the lower part still doing emmisions only. The 700 was replaced by the 707 which was the same as 700 but 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 competant 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 and in common with the Precision testers of that vintage had a wire wound control to set the line voltage. 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 quantites of heat at some settings and burnt out voltage controls on these early models is not unkown. 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 instead of the troublesome potentiometer. The model 82 is best avoided as it is inflexible so very limited in what you can test on it. They corrected this inflexibilty with the model 85 which is a  tester that produces excellent results and is very flexible.

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) so unless old TV's is your thing is of little practical benefit over the 151 and 157.

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  improved standard of construction over the previuos 45 models. All the model 45 range will do a good mutual conductance test with the 45B adding a gas test, the 45C adding extra selector switch positions and that increased the number of valves it was able to test considerably over the A and B variants. The 45D will do all the above and with the addition of a wheel type selector and have a stab at anode current as well means it will test a large range of valves. These 45Ds are considered in some ways a poor mans AVO. The 47A was a 45A with additional panel to read volts and ohms to make it into a sort of multimeter and the 46A was a 45A able to read plate and screen current.

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 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 as the range is limited and there is no flexibility. You will allways 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.

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 of course. The testers are relatively simple in construction,  reliable and will measure mutual conductance and indicate but not quantify plate or anode current. They are also limited to a maximum filament voltage of 40 volts.

Next from AVO comes the MK2 that has a one piece lift on cover then Mk3 and Mk4 that have removeable end covers and of course 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 applys 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 MK2 meter although looking the same externally is different from the MK3, 4 and CT160 one and not interchangeable.. If you buy any of these testers without seeing the meter move before handing over the money you are taking a big gamble as this is a common problem and the reason why a lot of these testers ended up in lofts 20 years ago. 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.

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 “itchinaka Mk2” 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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