Push pull amplifier – tube troubleshooting

Below are procedures that customer needs to complete to identify faulty tube, before submitting a warranty request:

  1. For Push Pull tube amps – 2 power tubes (either EL34 or KT88 – these are the most commonly used power tubes in push pull amps are used per channel. You may also see 2*300B or 2*845 type power tubes in recent years’ design)  Total 4 tubes are used for two channels together.

A floating piece of glass inside the tube – What is it?

If you have been playing with vacuum tubes long enough, you might have run into a situation that a new tube, shipped from a vendor, arrived with a piece of floating glass inside (see reference picture below). What is it? Where does it come from? Is the tube damaged beyond useful?

I tested my new tube in my tester, it’s drifting. Is the tube bad?

A: No, not necessarily.

A tube tester uses a pre-built circuit to test a vacuum tube’s technical specs DURING THE TESTING PERIOD. Many factors come into play when the tester gives you a tube plate current result (in mA). This testing period typically last only a minute or two – some tester has pre-heat phase (such as Amplitrex has 60 seconds pre-heat on auto testing mode), others may not or the pre-heat period is too short to have the tubes emitting stable stream of electrons (current).

Tubes may look the same – but test results are NOT.

In the past, most Chinese tubes (including high end tubes) are sold over internet without adequate distribution quality control. Some consumers are confused about the quality grade on the Shuguang Treasure tubes and wonder if all Premium tubes out of factory are the same, and if the factory test readings are accurate.

Can I hear the difference if tubes are tested different?

The answer is – it depends on the test results.

A weak (low) emission tube will last shorter time than a strong one. But you may not hear the difference when both tubes are within operating range. When a tube emission gets too low, the tube as part of the circuit is no longer operating at the optimal condition and will cause distortion in sound. It may also stress other parts of your amp causing equipment failure.

Tube compatibility issue

Please note that due the huge variation in tube amp designs, we as a tube vendor cannot guarantee our tubes are 100% compatible to your amplifier. Each tube model description on this website includes a spec sheet link – please feel free to forward it to your amp manufacturer to confirm compatibility before you make purchase.