Valve tester/ matcher really nessecary?

[diydidi]

I do mainly amp repairs, and not much building of guitar amps.
Is it necessary to have a tube tester or matcher?
I had a look at some of the newer types around. They go for around $500. I dont know if I can justify this amount of money. Will it be bringing me more work?
Any input views appreciated.

[Mick Bailey]

For me a tube tester is not something I'd bother with. Tube faults are pretty easy to diagnose 'in-circuit' and that's often a more reliable method than a tube tester that tests at (or below) spec-sheet ratings that are usually way too 'soft' compared to the voltages in tube amps. A tube tester may say an EL34 is good, but put that tube in a Traynor running 595v plate and nearly as much on the screens and it could be a different picture. One guy I really respect has a collection of tube testers including a really nice Mullard that uses punched cards to set the parameters. He doesn't use any of them because they don't exactly replicate the particular operating conditions of a tube in-circuit.

One thing I do want to build is a static burn-in/tube-matcher, just to match power tubes off current draw. There's a good schematic knocking about somewhere but it's just a PT, a few switches and 4 sockets. That's on my project list - just need to come across a decent PT.

[Justin Thomas]

When I bought my Eico (666 or 667, don't recall which, which shows how much I use it...) the previous owner had assembled a binder of his own settings for the common guitar amp types. Figuring out as best I can, it was to closer simulate the conditions in an actual amp, instead of the wimpy ones set forth in the actual manual. I have also read that the book that came with mine was fraught with errors - mainly pin designations. But I haven't blown up any tubes yet with it due to error.

I bought it because it was only $50, was in phenomenal condition, is a marvel of construction (to me, anyway), has just about every socket type, and it makes a fun toy. I do run untested used tubes through it, just as a short check. Everything else is for fun, and it WON'T test for hiss, hum, or microphonics. Which are the main problems we see in amps.

$500 for a new one? Pass. Unless you collect tube testers with a passion.

Justin

[DRH1958]

I use one(Hickok 800) sparingly. I like the life test so you can reasonably know how long to expect a tube to last and to find shorts in power tubes. I also use it when I buy used tubes so I can know if what I have bought matched what the seller said. I have found two EL84s that had a short to grid which I sent a pic to the seller and was sent repalcement or refund. This one will also find a gassy tube. Got it for a great price as it needed some calibration work which I did. Yes, gotta consider money spent. Not worth a huge investment for the average hobbyist.

[Mick Bailey]

Here's the circuit I mentioned. The heater supply is separate so the B+ can be varied using a variac.

Tube matcher schematic.pdf

[mhuss]

I wonder if a cathode bias setup might not be better for basic burn-in. No fiddling about with bias settings, just slam the tubes in there.

[nickb]

I do mainly amp repairs, and not much building of guitar amps.
Is it necessary to have a tube tester or matcher?
I had a look at some of the newer types around. They go for around $500. I dont know if I can justify this amount of money. Will it be bringing me more work?
Any input views appreciated.

For general repair work it's hard to justify the expense. The only merit of a good tester is the lifetime test to give an early warning indication of likely failures. For customers that need to know their amp is in the best possible shape this is something I like to do.

I have a couple of testers that I have built or acquired so I'm fortunate that I'm able to do this. I got them for other reasons. One, I can control from my PC and I routinely use it to test customers' tubes under real conditions - it goes up to 400V and 400mA. It gives me a nice printout report that I can hand to the customer as a demonstration of the tests done. I also use the data to compare with if the amp comes back for service.

If you are buying tubes in bulk for incoming repairs or sales, then some means of testing on arrival is important to allow claims to be made promptly. To be effective you have to check for noise and microphonics too. Then there is the issue of burn in and matching. Burn-in is done by running the tube at 7V for at 24 hours (some say more, some less), preferably with a small plate current to prevent the build-up of cathode interface resistance, although having spoken with a manufacturer of one of the burn-in rigs they don't generally use any plate current.

If you're dealing with lots of tubes then you need to get serious with incoming testing. I'm currently building a test and burn-in rig that will handle 18 octal tubes, test up to 1A at 500V and is PC controlled. I have the schematics done, the firmware written and a simple console type interface to the PC. I have also written a Python script that will take all the data and search it to build a table of optimal matches. I had realized a while back that there is a big weakness in the way tubes are currently being matched and I plan to capitalize on that. I'll be happy to share the design once I have completed it. Here's a crummy pic of it so far.

[hylaphone]

nickb, that is so cool.

In defense of tube testers, they are just another tool in the arsenal. Not necessary, but very useful IMO. And some more so than others...
I routinely use two testers (a TV-7, and B&K 747), each have their merits - as well as a plate current matching rig similar to the one mentioned above.
Also a home built noise/microphonics tester which hooks up to the scope to test each section of a dual triode equally.
I do sell tubes from time to time, so these are mostly QC tools...
For repair work, I find them convenient mostly as a go/no go test for shorts, grid emission, life, etc....

[Enzo]

As a repair tech, if I suspect a tube, I can plug a new one into the socket in seconds and find out if it makes the difference I need. Far faster than taking out the tube tester, setting it up, and trying to measure the old tube. Plus all the things a tester cannot promise you, so I never use the thing.

[Leo_Gnardo]

What Enzo said ^^^. Mostly I use the tube tester to confirm a tube is really bad - internal short, open screen grid connexion, like that. Also to do a brief check for baddies when a customer brings their own, especially used tubes, before they cause havoc in an otherwise working amp.

I converted an old Heathkit W4 amp to do real life tube testing once tubes have passed an initial "tube tester test." Some washouts there too, tubes noisy or causing oscillations. Admittedly, not everyone has space or budget for 2 levels of testing. Most informative tester is the amp.

[martin manning]

Here's the circuit I mentioned. The heater supply is separate so the B+ can be varied using a variac.

[ATTACH]37034[/ATTACH]

If all you need is matching and burn-in, this will do it. It would be more convenient than using an amp and wouldn't be expensive to build using a salvaged PT. I would add small plate loads and grid stoppers to prevent oscillations. You could also add a 9-pin socket and a rotary switch (or two) to set bias points (using 1% resistors) for selecting !2A_7 twin triodes with matched sections.

[ThermionicScott]

My Seco 107 and Hickok 533 are fun toys. I don't mind finding an excuse to get them out.

Shorts are really my main concern with sticking an unknown tube into an amp first.

[Justin Thomas]

I was just reading the RC30 tonight about tube testers; from what I gathered in that book, they're useful for checking for shorts, and not essential for much else. As in, they really have their limitations, there were no set standards for how and what they did, and the best way to test a tube was to plug it into the actual circuit... obviously, I doubt many of us have the lab-grade tube testers that the tube manufacturers used to have and use, so I am not talking about those.

Justin

[Enzo]

Yes, like any tool, it has limitations. And if you understand those limitations, it has its uses. The problem arises when someone thinks "tube tester" means it will be the definitive statement on whether a tube is "good" or "bad". What the tube tester says is only a small part of characterizing a tube.

[mikeydee77]

I have a home made Sussex tester from the vintage wireless forum. Cost about £250 to build and is essentially an AVO with digital meters. I learnt a lot from building it especially about oscillations.

I use it about twice a year to match valves or test unknown valves found in the shed.

Precision matching of tubes or PI could be a commercial angle to exploit. Valve retailers don't seem to publish their matching system or I haven't noticed it if they have.