Vintage Tube and Transistor Tester

[Joe Hart]

I also picked this up today. I thought it was cool but, like the oscilloscope, I know very little about it. Nice find or not?
-Joe Hart

[iccaros]

Does it work? If so nice tester

[Joe Hart]

I wouldn't even know where to begin! And I don't want to electrocute myself or burn my house down. Or blow some perfectly good tubes.
-Joe Hart

[PRR]

Short answer: eBay it, and don't let it go cheap. It's a modestly valuable machine.

Long answer:

All tubes have some combination of the usual pieces: heater, cathode, grid(s), plate. However 50,000+ different tube-types exist and the same pieces are not wired to the same pins. So you must patch the piece-test circuits to the correct tube pins.

The wheel next to "Leakage": turn it (gently!). That scrolls-through a long-long list of tubes in the little window-lens. Find your tube. It tells which socket and which patch-switch settings to set. Yes, it is coded cryptically and you really should have the manual.

BTW: if you go back, look for the pile of manuals. "Always" look for this when clearing cast-off electronics. The docs are as valuable as the gear. Some geeks actively toss that fluff, but others pitch them to a back shelf to sit untouched for 40 years.

Tube heaters can be 1V, 6V, 117V, etc etc. The scroll tells you where to set that switch.

Now you plug in the tube. (There *could* be more steps on that machine. Generally do what the scroll tells you; most of those cryptics are for a reason.)

A glass tube should be seen to "light up".

Now you press some buttons, one for each tube element. These connect 100V through a neon lamp (in this case, the meter?). The lamp should stay dark (meter stay left). Any glow/rise means the tube leaks. If it glows-bright/slams, the tube is shorted. Since there are at least 12 ways 4 elements can short, there are several buttons. This is IMHO the main reason to possess a tester: to find dead-shorts before you smoke an amp. (Saved my butt once: a 7027 tube was OK cold but shorted when heated.)

No short? Now comes the money-shot. This is where you sell the sucker/customer a new tube. Press a button, the meter needle swings into the GOOD zone (or not).

Digression: there's two types of testers.

An emissions tester simply wires most of the pieces together and sucks the MAXimum current possible. This is like testing a car by jacking it and flooring the gas. It will find totally-dead tubes. However it is also tube-abuse. Some sellers will not accept returns if an emissions-test is done. And in audio we "never" work a tube to the MAX. I know my car can do "110MPH" on jacks, but it's all 55MPH roads here. If the car willingly goes over 55MPH, I don't care what the MAX is, and it isn't good to try it. And BTW a dumb no-gain resistor can "pass" this test (though fail the shorts test).

A Mutual Conductance tester is better. It biases the tube to some high but reasonable (and safe) current. Then it wiggles the input grid, and meters the plate output current. This measures actual signal gain, and the scroll tells what is "normal" for that tube type (a the conditions in that tester). It's still not 100%. It tests power tubes like a radio played medium, not like a Marshall played LOUD!! And it will not tell you how much hiss or hum or microphonics. It usually won't tell you if a tube is OK cold for the first 20 minutes and then opens/shorts/sizzles when FULLy-hot.

It is a useful tool for sorting boxloads of tubes for re-sale.

IMHO a more useful "tube tester" for *guitar amp* tubes is a wide-open Fender Champ. Wire both octal and mini sockets at both positions. Note pin-voltages and "sound" with healthy 12AX7 and 6V6. Stick in your tube to test. If voltages go way wrong, or sound is way off, that tube seems sick. You must make allowances for 12AU7 taking more current and giving less gain than 12AX7, but a Champ is playable with 12AU7, just makes you work harder.

[amptramp]

As Paul said, there are emission and transconductance testers and since yours has a scale in micromhos, it appears to be the more desireable transconductance tester and it says "dynamic mutual conductance" on it, so it is one of the best.  It looks like it will take anything from old 4-pin up through compactron and nuvistor devices that were at the end of the tube era, so it is quite valuable.

The roll chart on the bottom has the switch and pot settings for each tube to be tested, so you scroll to the tube type, set the switches and plug in the tube.  When it warms up, you get a reading.  Some testers have separate instructions for testing shorts and leakage since a shorted tube may damage the tester, so there may be two steps: test for shorts/leakage followed by test for gain.

[tubelectron]

Well, I have some advice on the tube tester question as I use them very often :



I had many others (Eico, Hickok, Triplett, AVO) but I only kept these ones as these are... simply useful...

On that picture, you can see :
- far back :  late 60's METRIX 310 CTR
- far left : SECO VT grid current tester
- center : Ge/Si transistor tester based on a tube tester principle
- front left : HICKOK 600 from the early 50's
- front right : KNIGHT 600A from early 60's

The METRIX 310 CTR measures the plate current under tube manufacturer's datasheet conditions, so you can derive many other tests like transconductance, grid leak, etc...
The SECO VT is intended to test grid leak of the tubes (think Iceo on Ge transistor, to have an idea), but only preamp tubes, on a Good/bad schedule. This reduces its use.
Let's forget the Ge/Si transistor tester...
The HICKOK 600 (older but close to the 800) tests shorts and transconductance, according to HIS proper datasheet and under HIS conditions, which have usually little to do with the tube datasheet.
The KNIGHT 600A tests shorts and emission, according to HIS Good/Bad statement, that is to say nothing serious.

The nicest is the HICKOK. The funniest is the KNIGHT. I barely use the SECO VT. The reliable one is the METRIX, because of its measurement principle referred to the tube datasheet.

My verdict : unless you want to troubleshoot and service tube amps, you don't need more than an emission tester in excellent shape, like my KNIGHT 600A, a Heathkit, an EICO, etc... You won't measure anything, but if it finds a BAD tube (red scale = BAD), chances are that that tube is really out of duty. Forget the other types, as they need correct calibration to operate (Gm/transconductance models like the HICKOK) and a good knowledge about tubes to interpret the measurements (plate current models like the METRIX).

If you are interested by the tube tester subject, see Alan Douglas excellent book "Tube Testers and Classic Electronic Test Gear".

A+!