Tube Testers

[martin manning]

Anybody making good use of a tube tester?

I know a few folks here have them; selloutrr's Amplitrex comes to mind. That's a really cool machine, but not a justifiable expense for a hobbyist. Seems like vintage testers are almost a hobby in themselves, and I don't believe they are all that precise even if well maintained. They often don't test under actual operating conditions, and sometimes far from it.

I've gotten along perfectly well without one, just substituting a known good device if there is a question, and it's often said that the best tester is the amp you're going to use the tube in anyway. However, I'm kind of intrigued by S Bench's DIY gm/mu tester, which does test under actual operating conditions, and could match output tubes and dual triode sections.

Any thoughts?

[Cygnus X1]

True to the actual listening test.

I was gifted a Hickok 6000A and now wonder how I got by without it.
Great tool IMO.

They can be found cheap, but be aware of servicing costs and calibration.

Mine was calibrated shortly before I acquired it and I have a set of tubes I use exclusively for checking the tester itself.
I don't advertise the tester is up to date for calibration since I don't have the certification on hand though.

[martin manning]

Nice gift! What is your typical use for it? Troubleshooting, routine testing to determine condition, or both?

Noise and microphonics aren't measured by most of the traditional-type testers, maybe substitution is still the easiest way to check that. There is a DIY noise tester that produces quantitative measurements (another S Bench design), it might be useful for sorting purposes.

[Cliff Schecht]

I have a Hickok 539B that was calibrated by the navy before I picked it up. I haven't cal'ed it since but I do use it often for relative readings (meaning comparing known good to questionable). I doubt it's that far off anyways and the built in wall-voltage adjustment/meter makes consistent readings easy to achieve. Not a super high voltage tester but fine for preamp tubes and most power tubes really.

[selloutrr]

For relatively low money maximatcher makes the industry standard power tube tester and recently after I hounded them for years released a preamp tester, I've head good things about though I'm lost as to why you would need to test 4 9 pin preamp tubes at one time unless it also doubles as an EL84 tester? I haven't had hands on with it.
I'm really happy with the amplitrex after hooking up the CVT scope headphones speaker power amp computer label maker and printer it makes testing quick and easy.

I agree with your view on older testers they are an art and a science all thier own. Plus most don't test at operating voltages amps use so even a tube that tests good is questionable.

You can build your own tester you just need volt meters and power supplies A bridge would also be helpful

[Ian444]

I agree with that, I have an old Taylor 45 tester, it works well but I can only compare tubes to known good ones. It is good for measuring the sections of preamp tubes too, and to select good balance between the two triode sections for LTP phase splitters for example. A friend had an amp that blew the fuse intermittently, surprisingly the tester identified a bad output tube within a minute, maybe that was just lucky... It is good for matching output tubes too, and I've found that the results from the tester closely correlate with what happens in the amp.

Despite all that, it is cumbersome to use, having to look up a chart for all the correct switch positions etc, turn the knobs in the right order and then read off the transconductance on the meter. Plus run it up with a known good tube first so I can compare results with the tubes to be tested. Its all sort of esoteric, I don't really know what's going on inside it.

I often think a very simple homebuilt tester with panel meters, a variable plate and screen grid supply, a variable bias supply, a filament transformer and 2 or 3 tube sockets would make a lot more sense. If you wanted to test an EL34 - dial up say 40V bias, 360V for plate and screen, and read the mA cathode (or plate) current. That would be very simple and efficient. Also the results could be directly compared to a datasheet curve if you dialled up the same voltages as on the datasheet curve. You can get Chinese panel meters from ebay for $9 shipped that work fine. Calibration would be easy, just check the panel meters with a good DMM. There would be no need to use a known good tube first to check the tester either. I think that 2 x VVR ccts would make good variable plate and screen supplies, or use a variac if you have one to do the plate voltage and a VVR for screens. The negative variable bias supply could be done similar to a fixed bias amp. I don't actually use the Taylor tester very often, but when I do, it is invaluable. Just my 2c.

If you want to buy a commercial tube tester though, or find one for sale cheap, I think the key is to get one that measures transconductance.

[martin manning]

Ian, the S bench gm/mu tester (see http://greygum.net/sbench/sbench101/) is similar to what you are describing, but it has an adjustable DC supply for the filament voltage, a constant current supply for the cathode, and it lets the grid float. Dynamic parameter gm is measured at constant plate voltage, mu at constant current, and you calculate ra as the ratio of those two. Any operating point (up to 300V and 50 mA) can be dialed in as you suggest, and the static grid voltage compared to the data sheet. I'm guessing with all new parts ~$200 to construct a nice one.

Sellout, the Maximatcher looks nice, and as a specialized device it's probably best for matching large numbers of tubes, but I think for the combined price of it and the preamp tube tester, I'd just go for the Amplitrex like you did.

[billyz]

I don't use a tube tester all the time but sometimes it is handy and very useful. I have found a few bad tubes, shorts etc. Which saved me much grief. Handy for finding balanced preamp tubes for Phase inverter applications. Also good for estimating tube life etc.
But it is no substitute for how the tube behaves in the circuit.
That being said I have a number of testers and always go back to the TV7/du.

It is also a good selling feature to add value to your service work. Clients are always happy to know I have one and use it. I do get asked to test tubes , it brings in other work for me.

[David Root]

I have used the MaxiMatcher power tube tester and the VTV Dual Triode Characterizer, as they called it, for years. Sadly the VTV is no longer made. Neither are exactly cheap, but both are reliable.

I started with an old tube tester but could never make it work reliably so I gave up on it. I think it was just too far gone. The modern digital stuff is more reliable and tests at real life voltages, which is essential.

I have bought power tubes "matched precisely on my "Old School X4200" recently calibrated tester" that were more than 5mA apart at 400V on my Maximatcher (good match) to all over the place (more typical). Just because two tubes match Gm at 150V or so doesn't tell you squat about what cathode current each will draw at 400V.

When I want NOS quads I buy them from a guy who will match them at the plate voltage at which I intend to use them. Expensive, yes, but that is the only way I know to get that matching.

[selloutrr]

300 volts is not true opterating voltage.

The amplitrex is amazing but said and done when hooked up to the fullest extent over $4500.

I also run the maximatcher power tube matcher great for fault testing and quick basic matching or pair and quad.

I own a VTV and a geo Kaye both are great for matching sides and microphonics in preamp tubes. I picked up the amplitrex because of the print out results for clients and keeping files as well as the curve trace function.

[martin manning]

300 volts is not true opterating voltage

It is for preamp tubes, but true, not for power tubes. Still much closer than all but the very best of the older testers though, I think.

[Andy Le Blanc]

What can you rig up in place of a tube tester? DIY

[selloutrr]

300 volts is pretty standard in most tube testers

what u can rig up other a tube tester - an amplifier as a basic good bad test and matching via bias drift. Or read above posts and build your own test rig.

[gearhead]

I have used the MaxiMatcher power tube tester and the VTV Dual Triode Characterizer, as they called it, for years. Sadly the VTV is no longer made. Neither are exactly cheap, but both are reliable.

The VTV is no longer made? Ouch. I have one and it is quite indespensible.

[FYL]

Sadly the VTV is no longer made.

The Tube IMP mini TT from the UK can be a suitable replacement.