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Hello, Nice to meet you... and welcome to my blog page on buying vintage tubes on Ebay! Let's talk amplifier tubes for a few minutes... and make sure you are able to purchase a pair or quad of 6L6GC, 5881, or EL34/6ca7 tubes which work properly together and sound good in your amp.                                            

 I get tons of questions about buying vintage tubes all the time, from people who may not be experts and just want to purchase something that will work right for them. Here's what you need to know:

 1) First and foremost is the concept of MATCHED tubes. Sadly enough, many people buying AND selling tubes as matched do not really know what this means or requires. An Ebay purchaser can easily end up spending a whole lot of dough on tubes which will not even bias up correctly in his/her amp... or just sound plain horrible. I SEE PEOPLE BIDDING TUBES WHICH ARE CALLED "MATCHED" ALL THE WAY TO THE SKY AND JUST SHAKE MY HEAD, WISHING I COULD SOMEHOW DO SOMETHING. Ditto people bidding "NOS" or New Old Stock tubes very high thinking that if they are new they will work well together. Buyers beleive they are buying what they need, and even worse most sellers think they are giving you what you need... a so-called "matched" set of tubes. Sad to say, nine times out of ten it just isnt true... and those are not good odds folks. Nine out of ten sellers out there obviously do not understand the simple concept AT ALL... erroneously beleiving that if two tubes read the same on their little testers that they are therefore matched. Here's some simple guidelines to help you in making a purchase of matched pairs and quads of vintage tubes for your amp.

a) Tubes must first be tested and matched for mutual transconductance (or gm)... a reading which represents the actual STRENGTH of the tube. For your tubes to bias up and sound good, they should all be doing close to the very same amount of work! Most testers out there CANNOT test for actual gm at all... they merely give a RELATIVE and misleading figure such as you see on auctions which say "with a minimum of 54, tests very strong at 98!". This my friends is your first RED FLAG of warning... a reading given in only two digits. This means those tubes have been tested on a small "suitcase" home tester like grandpa used to have out in the garage. This tells you the tube is not dead... but that's hardly enough information to match a pair of tubes! Testers which can measure actual gm will give you a reading in THOUSANDS. Example: "RCA blackplkate 6L6GC tube, tested very good at 5450 with a minimum of 3300". This tells you that your tube has been tested on a proper tester which can measure that mutual conductance. That other tube which "Tests very strong at 98" might well measure very diversely and WEAK on a proper tester! Sellers in general DO NOT have these testers because they are very expensive, costing from $750 and as high as $2500. Those little "grandpa's garage" testers go for about $50... you can do the math here. This is why properly matched tubes always get bid a bit higher on Ebay... because those people who know better need tubes which will work right in their amps. Those who don't have that knowledge get stuck time and again with muttly pairs and quads of mis-matched tubes. It's not even especially a scam, as most tube sellers dont know any better either. BUT NOW YOU DO!  Don't ever buy "matched" pairs which read out in two digits, or you are shooting in the dark... and the odds of those tubes actually matching is alarmingly LOW.

b) Even more importantly is the fact that tubes must ALSO be matched for current draw! This is something you see even more seldom on tube auctions, but is absolutely neccessary to match tubes!  This too requires knowledge and the proper equipment, such as my Maxi-Matcher. What you need to know/ask is this: what is the ma current draw readings of these "matched" tubes? If they cannot answer, move on to another auction fast! Also, even those expensive testers mentioned cannot test tubes at a load similar to what a tube will experience in your amplifier... they only apply about 150 volts. This is why they have to be tested with a probe in an actual amp, or tested on an additional device which applies enough voltage... again, like my Maxi-Matcher which applies 400 volts.

C) The more expensive testers like my Hickok 539C can detect shorts and leaks which the other small testers will miss. It also performs the "life test" which basically measures how a tube reacts to a reduction of current... and tells you if the tube has lots of life left in it or is on it's last legs (just because a tube measures strong doesnt mean it will LAST for long... so this test is very handy and re-assuring as per the LIFE-SPAN of your tube). Tubes which do not pass the life test get thrown in the TRASH around here. But sellers who have testers without this vital feature end up selling them to unsuspecting buyers like YOU.

To sum up:

Look for tubes which have been tested for actual mutual conductance, in measurements of FOUR digits, such as my Hickok 539C (widely regarded by many as THE very best tube tester out there).

Make sure those tubes have been tested for current draw (ma) at a proper test voltage (400+), on an expensive device like my Maxi-Matcher. 

Without these tests, you are likely going to be dissapointed in your purchase... with your tech telling you he cannot even bias these "matched" tubes in your amp!

ALL MY TUBES ARE TESTED ON A HICKOK 539C FOR ACTUAL MUTUAL CONDUCTANCE, AND ON A MAXI-MATCHER FOR CURRENT DRAW. All tubes must be without shorts or gas, and must also easily pass the Hickok life test. MY TUBES WILL BIAS UP EASILY AND WORK PROPERLY IN YOUR AMPLIFIER, NO GUESSING!

Thanks for visiting my page! Come see me at altarofamps dott Commy! Nothing for sale there, just lots of fun with old amps!

Best regards

Michael