there's a ton on the bay that are affordable but might need new caps, diodes, resistors. got an eico 667 for a c-note or less and it just needed 2 caps, 2 diodes and 2 resistors. gives a general idea to strength and checks for leakage. have returned many tubes back from sellers claiming: new, good, matched, no leakage...
There are certainly plenty of testers on eBay but unless you're working on tube gear regularly and buying a significant number of tubes there's not much point in buying a tester and using it for a one-time restoration project.
As for the Eico . . . I have an Eico 666, which is essentially the same tester except that it has sockets to test older 4, 5 and 6 pin tubes.
These were sold as "Dynamic Conductance" testers, not "mutual conductance". While they're a step above a common emissions tester, neither the 666 nor the 667 will give you a reading for mutual conductance, so they can't be used to match tubes for mutual conductance. Like most testers, they also won't give you a reading for current draw which can be important when matching output tubes. The importance of this varies, depending on the circuit.
Like a basic emissions tester the Eicos give you a Bad / ? / Good reading. But they're not much use when it comes to matching.
So if you've returned tubes that were sold as "matched" because their readings on the Eico didn't match each other, it's very possible that you returned some tubes that
did have matching mutual conductance readings on a true mutual conductance tester.
The best thing about them is their ability to test for heater to cathode leakage. Most testers will give you a "short / no short" reading but the Eicos will actually measure lower levels of leakage. The instructions also tell you what level of leakage is considered "acceptable" for different types of tubes. So some tubes that show no short on another tester may be perfectly usable even though a small amount of leakage can be detected by the Eicos. And a seller who claims a tube has no shorts is not necessarily being dishonest.
Their downside is that the charts that show the settings for each tube type are full of errors. There are different versions of the settings and sometimes the settings are wildly different and they return different results. Even the ones that were published as "corrected" settings are not totally reliable.
If a seller claims a tube is tested they should tell you what tester was used and what the results were. If a seller that uses one of these Eicos, or a basic emissions tester, claims to be selling "matched" tubes then they clearly don't understand the limitations of their testers. The tubes may be fine but don't count on them being matched in any meaningful way.
I consider the test results posted by sellers (such as on eBay) to be ballpark figures. I still use my Eico but I was lucky enough to find a Hickok, which is now my main tester. The mutual conductance readings it gives are always very close to what sellers advertise, even when the seller is using a different Hickok model or even a different brand of mutual conductance tester. Even two testers that are exactly the same can give slightly different readings.
Bottom line is that, while testers are useful, they all have their limitations and the performance of the tube in the equipment (amp, preamp, tuner, etc) under actual operating conditions is what really counts.
