The (not complete) list of amplifiers that need special attention

Note, this page is also linked from the Emission Labs factory page, and in that case we only refer to such amplifiers that can use the Emission Labs tubes, like 2A3 and 300B, etc. For other cases, this page also gives information about other tubes than Emission Labs, like KT88, 6550, etc.

We sometimes see that amplifiers can only work on particular tubes, but not on all tubes. In extreme cases it can even lead to the situation that an amplifier works reasonable still on the very old, worn out tubes, and makes problems when replacing those with new ones.

In case you see the problem with one tube of a pair or quad, the normal reaction is, you will try this tube in other sockets. If you do so, in can happen the problems shows with this one tube only. The next step is the conclusion, the "problem follows the tube", and from there you conclude "it must be the tube". This can be a mistake. So it is a wrong expectation, that if one tube of a pair or a quad will forgive an amplifier problem, that because of this any other tubes must also forgive it. Another situation can be, a quad or an octett works fine for some weeks, then the first tube develops some problem reaction, then another, and so on. Also here, the wrong conclusion "it must be the tubes" is a easily made. So all in all, this diagnosis requires some experience.

Here is a logical example, just to make this very clear. But be aware, with tubes many owners think and act the same way! Suppose somebody has a car, and he puts much too heavy load in it, very often, and he was never aware. He allways used brand "A" tires, to his full satisfaction. Then one day he changes to brand "B", which is an expensive, long-life tire. After three weeks, from the left side of his car comes a heavy shake noise while driving fast. Of course the owner is angry with the new tires. Not with himself. So he changes the tires from the left to the right, and now the shake noise comes from the right side. So "the problem follows the tire", and so "it must be the tires". Well we know that he should not overload his car. Even when he changes back to brand "A" tires, he can also get the problem, or he was having already some other kind of problems, that he never linked to the mistreatment of the tires. Now you wouldn't want to be the company who sold him the "B" tires, and this man comes in your shop with a set of broken tires, and he wants his money back, and nothing else.

My honest judgement is, that with amplifier tubes 50% of the tube problems we see are above nature, and with rectifier tubes that number is above 90%. As an practical example with tubes, suppose the filament voltage is too low. Some tubes still work perhaps, others may give a spark inside the tube. In cases like this, the "bad" tube is quickly blamed. However..... there is nothing wrong with this tube, and if this amplifier would have had the correct filament voltage, all tubes will work normally for a long time, as they should.

Generally you will best way understand an observation when looking at all these possibilities:

1. A tube can be not so good
2. An amplifier can be not so good
3. Your sales person made a mistake
4. Your service technician made a mistake
5. You made a mistake
6. Environmental problem, like Mains voltage is too high or too low

The following table, is some personal experience, how to best replace the tubes in this model amplifier, and it prevents frustration, back shipments and guarantee problems. We say these are good amplifiers, only when replacing tubes, you should care for the specifics as listed here.

Amplifier list in alphabetical order