Hello everyone.
What tube testing equipment can I buy that will allow me to reliably test 6550s, 12ax7s and 12at7s? I need to buy some vintage tubes and people selling matched pairs are charging a boatload. I’d rather buy less expensive ones on eBay and test them. I feel if I were to get a bad tube or two it would overall be less expensive if I can test myself.
Happy Sunday to all,
Stu
What tube testing equipment can I buy that will allow me to reliably test 6550s, 12ax7s and 12at7s? I need to buy some vintage tubes and people selling matched pairs are charging a boatload. I’d rather buy less expensive ones on eBay and test them. I feel if I were to get a bad tube or two it would overall be less expensive if I can test myself.
Happy Sunday to all,
Stu
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I use an AVO CT160 to check the characteristics of the valves I use. Like you plan to do, I purchase boxes of 100 valves at a time and pair or quad balance them.
There are many valve testers on eBay. Here's one that won't be far away from exactly what you require;
https://www.ebay.co.uk/itm/27662350...8xKR6K4T2tI0lUWEIU+ax59Q==|tkp:Bk9SR5Svl7iUZQ
There are many valve testers on eBay. Here's one that won't be far away from exactly what you require;
https://www.ebay.co.uk/itm/27662350...8xKR6K4T2tI0lUWEIU+ax59Q==|tkp:Bk9SR5Svl7iUZQ
If you will only use a few tubes and tube types, the actual circuit configured as a test bed will work fine.
For large numbers, a true transconductance tester is needed, with socket savers in the test sockets to be used.
A burn-in rack would be very helpful as well, since the characteristics will change after burn-in.
For large numbers, a true transconductance tester is needed, with socket savers in the test sockets to be used.
A burn-in rack would be very helpful as well, since the characteristics will change after burn-in.
You could borrow or rent a tester from a member of a local audio club, if you'd be testing them during a short amount of time.
But do all the testing within the warranty period on the tubes, and burn-in is still a good idea, since some could fail.
Of course, you could just buy a tester and sell it when you're finished.
But do all the testing within the warranty period on the tubes, and burn-in is still a good idea, since some could fail.
Of course, you could just buy a tester and sell it when you're finished.
Noone "needs to buy some vintage tubes". Better but new tubes with warranty and properly matched.
But if you want to do this for some reason, get an AVO or amplitrex. The total cost however is way above what
new tubes would have cost.
Though your initial question is about buying a tube tester, it appears that you're only testing a handful of types. As suggested by Rayma, using an amplifier set up as a test bed with a few useful test points is a good idea.
Or, if you have the interest to, how about making up a jig that will duplicate the intended use of the tubes?
Secondhand tube testers are something of a minefield for the unwary, some commentary here that might be of use: https://www.jacmusic.com/Tube-testers/index.html
Or, if you have the interest to, how about making up a jig that will duplicate the intended use of the tubes?
Secondhand tube testers are something of a minefield for the unwary, some commentary here that might be of use: https://www.jacmusic.com/Tube-testers/index.html
If you are contemplating a tube tester just for use to match them then be aware not all tube testers can do that, the vast majority of tube testers are basic emission testers and this type will not give you the info you want - 2 tubes with the same emission may or may not draw the same current, there is no way of determining the anode current with an emission tester, you will need a tube tester that can measure anode current at a specific bias setting. All of the Avo tube testers can do this, as can many of the Hickok models, to name just 2 - before buying do your homework.
An alternative is to use an amp that you may already have SE or PP both will do the job, most SE amps are cathode biased so you just need to fire up the amp and once the voltages have stabilised, remove any inputs and measure the cathode current, this can be done with a meter in series with the cathode or by measuring the voltage across the cathode resistor and using ohms law to calc. the current, power down - plug in the next tube and repeat, those tubes with matching (within reason) anode currents should be closely matched - it's up to you to decide how close a match you want ie within 2% or 5% or 10%.
If you have a PP amp then you'll need the output tubes to be separately biased ie if cathode biased then they can't use a shared cathode resistor they must use individual cathode resistors and fixed bias amps must have separate cathode current sense resistor (usually 1 or 10 ohms) in each tube's cathode circuit. The procedure is the same as with SE amps - no input signal - wait for voltages to stabilise - measure the voltage across each cathode resistor and use ohms law to calc the anode current. Some amps may have some sort of balancing adjustment, in this case use this to set each grid to the same voltage/bias setting and then measure the voltage across the cathode resistor. If 2 tubes have the same anode current at the same bias voltage then you can assume they are a reasonably close match.
Using an amp is no where near as convenient but is a workable alternative to spending $1500 or more for a tube tester.
An alternative is to use an amp that you may already have SE or PP both will do the job, most SE amps are cathode biased so you just need to fire up the amp and once the voltages have stabilised, remove any inputs and measure the cathode current, this can be done with a meter in series with the cathode or by measuring the voltage across the cathode resistor and using ohms law to calc. the current, power down - plug in the next tube and repeat, those tubes with matching (within reason) anode currents should be closely matched - it's up to you to decide how close a match you want ie within 2% or 5% or 10%.
If you have a PP amp then you'll need the output tubes to be separately biased ie if cathode biased then they can't use a shared cathode resistor they must use individual cathode resistors and fixed bias amps must have separate cathode current sense resistor (usually 1 or 10 ohms) in each tube's cathode circuit. The procedure is the same as with SE amps - no input signal - wait for voltages to stabilise - measure the voltage across each cathode resistor and use ohms law to calc the anode current. Some amps may have some sort of balancing adjustment, in this case use this to set each grid to the same voltage/bias setting and then measure the voltage across the cathode resistor. If 2 tubes have the same anode current at the same bias voltage then you can assume they are a reasonably close match.
Using an amp is no where near as convenient but is a workable alternative to spending $1500 or more for a tube tester.
No it isn’t. It is an emission tester as described above. It cannot establish matching. They have their uses, and I use one, but that isn’t one of them.
I built myself the Utracer kit. Etracer is another option.
https://www.dos4ever.com/uTracer3/uTracer3_pag11.html
https://www.dos4ever.com/uTracer3/uTracer3_pag11.html
+1 for the uTracer. Very happy with mine, and the instructions for building are excellent. It really surpasses older style testers when you need to match dual triodes. Since screen and anode supply and sensing circuits are the same you can test both halves of the triode at the same time, and plot on top of each other. I do have an AVO mk3 that is very useful with easy setup for any type of tube, but that is a bit more of an enthusiast's machine since it needs a bit of care and is quite bulky.
This is more complicated than most people think. What @ Retailer said is true.
Many tube testers can test or pair small signal tubes like 12AX7s. Not so with power tubes like 6L6s.
I wrote a long blog post about this a while ago. Anyone inexperienced with tube matching might benefit - and save your output transformers:
https://www.russoldradios.com/blog/testingmatching-audio-output-tubes
Many tube testers can test or pair small signal tubes like 12AX7s. Not so with power tubes like 6L6s.
I wrote a long blog post about this a while ago. Anyone inexperienced with tube matching might benefit - and save your output transformers:
https://www.russoldradios.com/blog/testingmatching-audio-output-tubes
Thanks for the link that was a great post. Very informative. That's mostly what I wanted the tester for. I wanted to check if the vintage tubes I were buying would test well enough to put in the amplifier, where ultimately my ears would be the test. Does that make sense? Trying to get ones with similar voltages or data to check.
If you are on a limited budget then you may want have a look at this :-
https://valveheaven.com/category/test-equipment/
A lot of these have been built, not real fancy but reading the comments they do the job - it may be all you need.
https://valveheaven.com/category/test-equipment/
A lot of these have been built, not real fancy but reading the comments they do the job - it may be all you need.
lol!
Hi GobbleStoo,
Your ears will never be a good test. You are not a test instrument, but you can compare things quickly.
If something sounds bad, it will test terribly. Been down this road with real people so often now ...
Hi GobbleStoo,
Your ears will never be a good test. You are not a test instrument, but you can compare things quickly.
If something sounds bad, it will test terribly. Been down this road with real people so often now ...
Emission testing is of extremely limited use.
You need to measure transconductance.
You need to measure transconductance.