Category Archives: ~Tube FAQ & Must Read ~

A: Answers to this question is related to your budget, as well your desire for the level of sound improvement.

The general rule of thumb is:

1) Upgrade the pre-amp tubes first. These are typically the smaller tubes at the front of an amplifier (power tubes are typically at back closer to power output transformers). A sound signal from your source component (such as CD player) is sent into the amp for amplification – preamp stage is first amplification stage so money spent on upgrading preamp stage tubes will give you great improvement. Garbage in, garbage out. If you don’t get great preamp signal, you won’t get great final output signal to speakers.

2) Once the signal being amplified at preamp stage, it is further amplified at the power tube stage. If your budget allows, get the power tubes upgrade to the extent that your wallet is happy and your ears are happy too. Most common power tubes are EL34, KT88, 300B and 845. The price for these tubes are in the same sequence from low to high.  Read more...

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).

Tube is a live creature – when heated, it emits electrons and work in a circuit; when not heated enough, it will generate electrons but the quantity may fluctuate overtime then stabilize. A short testing in a tube tester will not definitely tell you if a tube is drifting (i.e. current keep changing) or not. Drifting is term used over extended period of usage time – not over a minute or two of testing in a tube tester, especially an old tube tester that hasn’t be calibrated for years with aged parts inside which could cause significant error in testing results generated.  Read more...

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.

Below is the sample testing results for Shuguang Treasure tubes that Grant Fidelity receive from factory in 6 months of time (Jan 2009-July 2009). They are self explanatory as you can read all the testing results obtained by Grant Fidelity’s 5-spec test. 1) Listing results are listed in the order of factory matched pair or quad (shaded or unshaded in the spreadsheets). If a tube is listed as single or a quad is not complete, it means the other one(s) have failed in our first test and graded as ‘Rejects”. 2) “Rejects” are not included in the list as those tubes are reported with ‘Short’ in the tester, hence no further results can be reported. 3) KT66-Z and 2A3-Z tubes are not as popular as other models, so they are not included as we don’t have sufficient data to deem the testing results as representative.

Shuguang Treasure 300B-Z:  Read more...

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.

Noise / micro phonics issue on a preamplifier tube can be heard. Micro phonic is common on large power tubes but it is not important for sound quality.

Heater-to-Cathode leakage cannot be heard, but it will kill the tube faster before you know it.

Excessive gas will certainly shorten the tube life – but you cannot hear it.

A set of tubes with bad matching may cause distortion in some cases and become audible.

Do you need perfectly tested and matched tubes? Not always. You have to find the balance point yourself. Not everyone is perfectionist, but a seller should make all information known to let the buyer to make informative decision.

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.

We cannot make recommendations on tube substitution on a particular amplifier model due to liability reasons. Your amp manufacturer or distributor is your best source of information on such a topic.

Please also check the physical measurement of the tube you are about to purchase, especially if your amp has limited space for installing tubes. Some amps have recessed chassis which could limit space available to install different tubes.

Returns due to compatibility issue listed above will be subject to 20% re-stocking fee at all circumstances.

Thank you for your understanding.

Some tubes at start up will have a metal like sound from inside the tube. This is the plate materials being heated up and expand – this sound will disappear once the tube is turned on for a few minutes.

Such a sound will happen at each time you turn on the tube – i.e. at each heat up process. This is perfectly normal and it doesn’t indicate bad tube quality or whatsoever. It’s a natural process of metal expanding under extreme heat.

Some tubes have this sound, others don’t because each type / make of tube might be using different plate materials.