Old tube testers - worth getting?

[waspclothes]

Hey guys,
A few friends have started to ask me to look at their tube amps, and one question people ask a lot is "do my tubes need replacing?". Some guys look like they're running the original tubes in their amps, but the amps are still outputting sound, so I generally say "no". Since I can't test tubes, I can only really give a Go/No-Go type response. But I'm wondering if there's a better way to answer them.

I see that Orange makes the VT1000 which is a modern tube tester for a crackton of money. There's a lot of old tube testers on ebay, but I don't know if those do any useful testing that would help me. So my question is:

- Are old tube testers easy to refurbish and get working correctly?
- Do old tube testers give me important info on a tube that my ear (or multimeter, oscilloscope) can't?

[Enzo]

The best tube tester there is, is an amplifier. I ran a commercial pro audio shop for 30 years. I have a tube tester, I am using it as a footrest as I write. It works. I never use it. In my view, tube testers can verify a tube is BAD, but cannot tell you a tube is GOOD. The conditions a tester puts on the tube are not real world conditions. It will give a good/bad meter reading, but that is almost worthless. The tester can find shorts and gross issues, but won;t tell you the tube is noisy or microphonic or just lost its tone.

Power tubes wear out, it is normal. The small tubes rally don't. They can last decades. They fail, meaning the get noisy or microphonic or just stop working, and then we replace them. But power tubes are like strings, they keep working long after they lost their tone. So keep a set of power tubes you know work. You can plug them into an amp to see if the original tubes are a problem.

AMp working is one thing, amp sounding fresh and alive is another thing, and that is why we replace power tubes. On the other hand, if those 25 year old 6L6s in some amp sound good to the guy, hell, keep using them.

[waspclothes]

AMp working is one thing, amp sounding fresh and alive is another thing, and that is why we replace power tubes. On the other hand, if those 25 year old 6L6s in some amp sound good to the guy, hell, keep using them.

Thanks for the reply Enzo. Is there any way to measure this "sounding fresh" thing to actually quantify it? Any indicators that can be measured?

[drewl]

He's right.
I had a tube tester in for repair and decided to check tubes I had lying around- good and bad.

Tubes that failed on an amp tested good, and as mentioned it doesn't tell if a tube is noisy or microphonic.
Neat gadget to have around? Sure!
Needed? Probably not.
But hey, if you can get one cheap, why not. And impress your friends!

[Leo_Gnardo]

Orange makes the VT1000 which is a modern tube tester for a crackton of money.

And that's exactly what you're going to need to find out what you need to know about tubes you may want (or not want, depending on the result you get) to use in guitar/bass amps.

There are some rare old testers, AVO brand mostly, that are more useful than the typical "pin ball machine" testers commonly found. But they are rare, require some serious maintenance, and working ones aren't generally given away or sold cheap.

I have my Knight which is more or less a Hickock, and all it does, is confirm tubes I think are shorted are in fact shorted. Other than that its usefulness is very limited, and sometimes goes unused for months at a time. If that's not enough, I was just given another, stored in a basement or barn until the box around it fell apart from mold. Oh boy! One more boat anchor to add to the collection....

Some of my customers have asked me to test bags & boxes of old tubes for them, to "confirm" they're all right so they can flog them on ebay & elsewhere. Of course nobody wants to pay for my time doing this. Just as well, the answers they get from the old Knight/Hickock wouldn't be much good anyway.

[Justin Thomas]

Tube testers are FUN, but not particularly useful. Maybe for rough-checking oddball tubes for experimental designs that fit no commercial amp?

I've got a really nice Eico 667 in great shape, with the book and also the previous owner's homemade manual with corrected and more realistic operating conditions for all the guitar amp tubes - mostly increased plate and screen voltages. I haven't had the courage to try those settings out yet, though. I've heard the Eico manual was riddled with errors, but I haven't blown a tube yet that wasn't MY mistake. Note - I have an early model, without the thumbwheels for the specs.

That thing has so many knobs and buttons and switches that if anyone asked me to test a random box of tubes I'd pop them! But it is pretty universal, takes Compactrons & Nuvistors, and even some first-gen transistors. I <DON'T> want to ever have to fix it, though!

Justin

[tedmich]

People like the old USSR KALIBR L3-3 tube testers, but they are more $ than the Orange usually. I'd listen to Enzo, but that said I too have a foot rest

[52 Bill]

I own a couple of old B&K Dynas that I inherited from my father and a TV-7 that I got maybe 20 years ago. I use them maybe 2 or 3 times a year, when I get something in with oddball tubes that I can't plug in a substitute for.

When friends ask me to test a bag of tubes, I will offer to set up the BK and let them test themselves. That way they can have all the fun.

[DrGonz78]

The one reason I got a tube tester is to test tubes for gross shorts and major failures. I only use it if I testing a box full of old used tubes to pick out the spoiled apples. I might use it one day for a foot rest but I tend to stand up at my bench and when I sit my rotating salon type chair has a foot rest already.

[nsubulysses]

Tube testers are FUN, but not particularly useful.Justin

Agree. Sometimes fun stuff happens.

Makes it easy to know which one to NOT put back in the SVT Classic when the customer says "I don't know if this works but I need to sell it and I haven't used it in at least 7 years," or something like that, and the fuse is blown.

[Mick Bailey]

Is there any way to measure this "sounding fresh" thing to actually quantify it? Any indicators that can be measured?

As you already appreciate, just because a tube is old doesn't mean it's no good. Age doesn't count. Hours of use are what matters.

The first thing is to look at the physical condition of the tubes - any cracks to the bases, loose base/envelope bond, burning or discolouration. Is the screen printing bleached out through use? Reds go pink, whites go yellow-brown, gold goes silver-grey. Is there any sign of the gettering turning white around the edges. Tap the tube on its side and rotate it - any dandruff flakes? these indicate a breakdown of cathode material. Any brown staining on the inside of the envelope? Any shadowing around the apertures, especially with EL84s? Any of these indicates a tube that's had a life. A tube tester won't tell you any of this. It seems a long list, but with experience you can appraise a tube in a few seconds.

If the tubes look OK and are worth keeping because of the brand or type, do an output test. Does the amp make a decent amount of power? You wouldn't want to dump a perfectly good set of GE KT66, RCA black-plate 6L6 or Mullard EL34s. While the amp is powered, tap each tube - any excessive rattles or microphonics?

The final test is 'does the amp sound good' If it makes enough power, the tubes look good and it sounds good, then there's probably no reason to replace the tubes. But also look at the type of player. A hard-gigging pro who's just bought an old amp he/she wants pressing into service will want reliability. You may recommend the old (but still good) tubes are saved for another day and you install a new set. On the other hand, a bedroom player may not get any value out of changing the tubes. Equally, a studio may want to maintain the existing sound of the amp and be nervous about anything that changes it. Especially if an artist keeps coming back to use the same amp.

I keep a bench set of tubes that I know and rely on. They give me a baseline. If I have any doubts I'll sub in those and do a back-to-back test just to make sure.

[John_H]

The one reason I got a tube tester is to test tubes for gross shorts and major failures. I only use it if I testing a box full of old used tubes to pick out the spoiled apples. I might use it one day for a foot rest but I tend to stand up at my bench and when I sit my rotating salon type chair has a foot rest already.

I'm with Dr G on this. I have an old Triplett tester that I paid a whopping $15 for. It usually lives under the bench, but I like to test everything that I'm unsure of. It's great for detecting shorted tubes.

[Drewline]

I have a Century FC-2 tube tester which I inherited from my Father years ago. It is an emission tester. All I use it for is checking for shorts. I test preamp tubes for microphonics in a reissue Champion 600 which has been modded by removing the tone stack in the manner of an old Tweed Champ.
Power tubes get tested in the amp with a light bulb limiter on.

[Enzo]

I do keep mine hidden under the bench, not just as a foot rest. If customers ask "Do you have a tube tester?" I just say "You're talking to him." If they know you have a tube tester, they expect you to use it, and yes, they bring in bags of tubes. And even if I took an hour or two to test them, all I can tell them is they are not shorted.

I ask this: do you need a tester to know your strings are dead? I know what fresh tubes sound like. Take an amp that works just fine but has old power tubes. Play it for a half hour to get the sound in your head. Now swap in a new fresh set. I bet you hear a brighter more lively sound. if not, stick with the old tubes.

And there is no test anywhere that will tell you if a tube is going to fail tomorrow or next week or next month. Any tube can fail at any time.

[mozz]

They are good to have. Test showing leakage may work fine in a amp, for a while, but its going to get worse.