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Am I the only one who gets upset about misleading tube testing claims on ebay? I have occasionally sent messages to some ebay sellers but I'm generally ignored so I thought I'd post here and bring an example of one of these misleading auctions to everyone's attention. I've seen quite a few auctions where the seller uses an Eico 666 or 667 tester and quotes mutual conductance figures for the tubes. These testers are called "dynamic conductance" by Eico, which is nothing more than a slightly advanced version of an emissions tester. I have a 666 and it is fine for what it is, but these testers are NOT mutual conductance testers and they are incapable of determining if tubes ar truly "matched". It may be that some of these sellers are initially misled by the "dynamic conductance" label, but even after I point this out to them they continue with these claims. Also, a testing number (emissions or true mutual conductance) is useless unless you know what the value for a new tube should be or at least what the "good" range is for that tester. In the auction linked below the seller not only claims that the numbers are mutual conductance and that the tubes are matched (82, 80, 80, 80), but he also fails to mention that on the Eico tester that 80 is the lowest reading in the "good" range! That's not to say that the tubes don't have some useful life in them. I've had tubes that test in the ?? range that sound fine. But if you see claims like this using these Eico testers, beware . . .
Follow Ups:
Yes, I think that description is not too accurate.
I sell tubes on E-bay and A-Gon every so often, because I have too many, not because any dealers don't want them - quite the contrary.
I assume that the potential bidder knows what he is looking for and therefore provide as much relevant, accurate test info as possible - first through a 539C then through an amp at anywhere from 250-500+ plate volts for current draw at a constant -grid voltage. Now, is this an end-all and last word on how those tubes are going to test out in various other testers and amps? Of course not! Every amp and tester is different. Yes, power tubes through the more common suitcase testers will only give a relative comparison to each other at reduced voltage levels - so that shouldn't be used to state "matched" (that term IMNSHO has been abused to the point of being almost meaningless).
Not every E-bay/A-Gon tube seller is a schmoe looking to rip people off.
Statements claiming matched pair and test good. The last one almost assures a weak tube. The first claim may ultimately mean two poorly triode section matches or just not matched in a high percentage of cases. It seems that about 50% of these sellers count on you not being able to tell. I am listening to "test strong" tubes which are in fact marginal VT231s (?) mark tubes, but they do in fact play fairly well.
I have been sold all sorts of garbage as it turns out. Tubes that are supposedly NOS on ebay never seem to test anywhere near that, whereas reliable dealers test NOS strength, or better.
One experienced tube-o-phile and former dealer told me ebay is a dumping ground for tubes that can't be sold to retail dealers because they no dealer would accept them. He did say, however that as many as 50% are actually not bad tubes at all. so it's a crap shoot.
It wasn't until I couldn't rely upon using my friends gain only tester, that I finally gave in and bought a recently "just callibrated" tester of my own which I am in the process of verifying.
I got an inexpensive, Hickcok Mutual Conductance tester model 800 essentially the 600 without the socket island.
Since I collect mainly double triodes with low voltage operating conditions this is OK, but for power tubes I understand that these tests are not under real world conditions but it is still good at telling you if a you have a good or weak tube.
The question is why is there so much greed and dishonesty. I am a native New Yorker where our motto is "trust no one." Furthermore you are always asking yourself what is the angle this person is using. It really makes me wonder about my fellow man inmates excluded of course (yeah right oops.)
Still retail dealers of good tubes who simply will not be fooled still charge unreal markups. Some will buy large quantities and select out the few really good ones which is costly. The rest may be tossed while others sell the semi functional tubes you know where.
From what I understand they just don't pay much for the tubes they sell. Except typical mark ups on new production which is 50 points. i.e. twice as much as they paid but that is still better than 10Xs. Dealers go ahead and correct me, flame whatever, but I think I know the truth because a couple of people in the business told me similar stories.
It can be at times, but that dealer statement is a bit 'off the wall'. Use Paypal & get a full refund if the eBay listed tubes are not as described.As for dealers, they usually buy wholesale lots for good reason. Tube dealers do have overhead costs including advertising, carefull testing & matching services plus the time involved seeking those vintage tubes. eBay tubes are usually not wholesale priced or available in larger lots.
One will pay more most of the time with a tube dealer, but quality is usually assured & always assured regarding tube dealers like Jim McShane.
I have a 667, and it's a nice little tester, but geez. You can find at least two settings for just about any given tube, between the roll chart and the various printed charts and supplements. For the 12AX7, for instance you can take your choice of readings, many of which are probably erroneous. But look hard enough, and I'm sure you can find one setting to make your poor old tired tubes test just fine!
I agree. They probably are good, testing that way on his Eico, but those are not mutual conductance readings as implied.Even more misleading is the claim of being "matched". I have taken the time and effort to construct a six-socket matcher that actually measures current at various plate and grid voltages. This is the only way to determine if a set is matched.
Most tube testers (with the exception of a 539 and a few others) cannot do this.
Ideally, both current and mutual conductance should be measured before calling a set of tubes "matched".
Keep on tubin! Al
You are correct in that you should measure trans and current draw, but a 539C is not capable of doing this accurately at real world operating levels. I beleive that the 539C maximum plate current is about 130 volts, which is roughly 200 less than real world for 6BQ5s. If you really want to match power tubes correctly then you need a tester that goes up to about 500 plate volts which will cover just about every power tube with a few exceptions. No suitcase tester that I know of does an adequate job on power tubes.
It's worse than you point out - some sellers will simply say "tests good". Well, if they've gone to the trouble of testing tubes and are not prepared to list the actual results, what does that tell you?I got stung the other day for a bench supply described as "untested". Of course it had been tested and didn't work. The seller was rude and didn't give a damn. His other auctions showed quite clearly that when stuff worked it was listed as "tested and working perfectly". Sellers defense was that it was described as "untested". This could, in fact, be challenged in the UK under the sale of goods act, but I couldn't be bothered.
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