Tube Amps / Music Electronics
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|1/20/1999 2:59 PM|
Just this afternoon, I spotted an old, dusty, but in otherwise good shape tube tester in the local electronics store. The salesman says it still works fine and it is $65. It's about the size of a small typewriter, with a bunch of different tube sockets along the top, and various battery, diode, and other test jacks around the edges. There are two big meters in the middle, and 10 levers which resemble faders on a mixer except there are only 4 positions to put them in, labeled: Test, Open and two others which I can't remember. The most interesting feature is a scrolling reel of paper under a glass window near the bottom that contains the name of every tube known to man and which controls to use for each. This is controlled by a rotatable knob on the right hand side which sticks about half way out of the faceplate of the tester. Has anyone ever seen anything like this before? If so, would it be worth getting? I have a bunch of old tubes from various components which my dad had in our garage for some reason and I'd like to see if they're still good. Any info would be greatly appreciated.
|1/20/1999 6:44 PM|
The tube tester may or may not be worth getting - it depends on several things. First, the actual model and make, many tube testers were set up like you describe. Second, whether or not you have the expertise to calibrate the machine or are willing to pay someone to do so. The tester is at least 30 years old and possibly quite older. Carbon composition resistors drift with time as do paper capacitors - electrolytic caps dry out. The manchine will need an overhaul and calibration - if it is a common brand the schematic(s) may still be available.
Thirdly, why do you want a tester? If the old tubes you have are still in the box, then they are probably OK, if they are "pulls" the easiest way to "testing" them is to put then in circuit and see how they perform. Back in the days when the dinosaur carcasses were still rotting and I was a full time TV technician we "tested" a tube by pulling it out of circuit and replacing it with a known good tube. If the circuit improved the tube was bad if it didn't there was some other cause. The tube tester we had was primarily for customers who wanted to test their own pulls (someone woudl usuall pull all of the tubes out of their TV, test them in the shop and take them home and either not know which socket the individual tubes went back in or mess up the pins reinserting them.) Or so that we could demonstrate to the customer on a "scientific" instrument that the tube was actually bad and that we weren't trying to "ripoff" the customer by replacing the tube.
So, what's yer make and model and how much do they want?
|1/21/1999 12:37 AM|
The description reminds me of an old Hicock 539 series.
But, It could be anything odd like that from those vintage years.
If it is one of these old timers, like the Hicock, they are WAY cool and great instruments to test tubes with. A real hand full!
However, the tube chart will be old, and although youmight think there is every tube known to man, 2/3 of them will be tubes that no body has heard from in 30 years!.
And the device will need recalibration plus you'll desperatly need a service/owners manual to teach yourself how to use it if it's real tube tester and not a drug store buzz box.
The books are not that hard to find, they're out there, but you can expect to pay about $35.00 to $50.00 just for all that documentation.
There are still folks out there recalibrating and or rebuilding these great old pieces of test gear, but expect a $75 to $150 bill for that too.
Unless you are doing design work or matching lots and lots of your old tubes you've found, I'd pass and keep your eyes open for newer old Sencore or maybe even a decent old Heathkit.
The last workingHeathkit tube testor I saw at a ham radio swapmeet sold for $5.00 with a new updated chart roll!
|1/21/1999 9:10 AM|
Thanks for the advice guys. I probably won't buy it seeing as I have senior projects to spend money on this my final semester. If I had more money I'd probably buy it just because it looks cool.
|1/21/1999 9:35 PM|
||Re: How about a tube tester for guitar amp apllications?|
To Bruce and all:
Don't those testers just tell you if the tube is up to spec on a few selected parameters? Even if a tube meets those specifications, it may or may not sound good in a guitar amp- right?
Well, why don't we all come up with a tube tester design that is relevant to guitar amps? Like for 12AX7's, something that would tell us if a tube would sound and respond like a Telefunken or a Mullard or whatever (i.e. "dark and distorted" or "bright and clear").
My question is this: what parameters would we want to measure in a preamp tube and a power tube to determine how it would work in a guitar amp?
We all seem to know what we like in a tube, but it is all so subjective. What would we have to measure to make the selection process a bit more scientific?
P.S. I figure that if we all first decide what we'd want the machine to test, it'd only be a matter of time before someone actually builds a prototype! For starters, I'd like it to compare both stages of a 12A_7 tube to determine how well they are matched in terms of gain and distortion.
As for the design of the tester, it would need a power supply to heat the filaments and supply the B+. And it would probably need jacks to hook up a signal generator, a scope and a DMM or two...
|1/22/1999 12:37 AM|
Yeah, one of the worst thing about a standard tube tester, is a weak tube or filament sensitive tube might still sound GREAT!
A good lab type tube tester, like I mentioned before, can really give a tube a serious workout and measures all sorts of interesting and usefull things about the tube that a drug store tester can't.
The basic tests of, open or shorted elements and maybe if it's gassey, etc., isn't good enough for real testing.
But it's good enough for the quick and dirty "yes or no" test.
Your last descriptions of the ideal test machine is just like one of the testers I was talking about but built 30 years ago and still worth a bunch of money.
|1/22/1999 3:42 AM|
I ordered a bunch of old Glass Audio issues. In one of them somebody sent in A simple tube Tester/Matcher. Volume 7 Number 5 1995
Suppose to check if the tube is usable, and also checks for symmetry in duotriodes. It got a little chart for the common audio tubes and simple instructions. Parts count is really low and quite simple.
I can scan this in and send it to ya if your interested. Post if up for others if you like
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