How to tell if tubes are matched?

Well we have an old Heathkit that is capable of putting a load on the tubes and the manual will teach you how to grade tubes for transconductance in about a half hour - but then I suppose if I were doing it for a living I wouldn't want anyone to think it is too easy. As far as calibration, hmmmmm, well if two tubes have a reading within five per cent and have gain that is relatively high (after comparing perhaps 10 to 12 of their same kind AND THEN you listen to the ones you THINK are matched - you might just surprise yourself (and anyone else with ears ;-) After all the real test is how they sound or isn't that scientific enough, HA! Only thing this requires is a dozen valves and an old tube checker - anyone that describes it otherwise probably has some scientifically 'matched' tubes that they will sell you. I am still trying to figure out if the quality of the silk screening on the tube will improve the sound. I have seen some real beauties - good luck in any case. I have to get back to thinking about presence edge smear as it relates to original recording quality and what to make for dinner. I'm just a girl - what do I know ;-) ???

I don't wish to be difficult, but getting a tube checker is not a good short range idea. The old (and I do mean old) tube checkers that are most often for sale, are only useful to separate the living from the dead (and many fail this criterion). Suggestions to the contrary are misinformed.

1. tube checkers must be calibrated to be of much use in matching
2. tube matching is not an easy or quick art to learn
3. power tube matching requires more than simple transconductance matching, it requires proper loading as well, a facility few, if any, commercial units have. A match of 5% under a realistic load is the usual standard.

If your serious get a tube tester from Ebay. We matched gain on 12AX7's for our Jolida hybrid and found it to be WELL worth while. If you have 6L6's or KT88's in the final - you will find a good used tube checker a valuable tool. We matched tubes for our older Conrad Johnson PremierII - also could hear the difference.

If the output tubes are way off, you might have problem adjusting their bias. But in general, there is no way to tell if the two tubes are matched without running them through test equipment.

Just a follow up. Some Amp manufactures will hand write the matched pair #s and socket# on the tubes with a marker.In any case they are marked in some fashion. This is because they have also set the bias voltage for the power tubes.

Jim

Relax. This is not a new problem. Normally only output (large) tubes are matched. If input (small) tubes are not marked "left" and "right" etc., it won't matter. The output tubes will be marked as pairs in some fashion. Before you rip the boxes open, look for rubber bands holding pairs (or quads) together. Alternatively, the boxes themselves will be marked. I store my tube boxes in the exact same order that the tubes are installed in my amps, so if I try another set ,the tubes always go back in the original boxes. Stay cool, and if when your amp arrives you are not certain, post again with specifics, and somebody will walk you through it.
Do make certain that you plug the small input tubes in the correct sockets, if you get them backwards (i.e. put the 12ax7 in the socket intended for the 12at7, the darn thing might not work. Read the instructions concerning output tube bias carefully before you proceed. Tubes are tough and will withstand abuse, but improper bias will kill them off in a hurry.
Finally, tubes have been around for almost a century. If they were difficult and delicate flowers, they would have been abandoned long ago.

First the tubes are packed in their own boxes. Each box will have the respective tube socket number written on each of them. Or at least each tested match pair. The owner’s manual will have a block diagram showing the tube layout. Your amp may even have the socket number stamped be side each of the sockets. This is for a new amp. If you are buying a used amp, hopefully the seller kept the original tube boxes, and as he pulled the tubes out put them back into their respective box. Or at the very least identified them in someway. If they are not identified...contact the seller.

Is this amp new or used? If used there is more you need to know.
Jim