Category Archives: ~Tube FAQ & Must Read ~

How to bias my new tubes in my amp to replace the stock tubes?

multimeter for biasA: Congratulations for getting new tubes for your precious tube amp. Chances are either your stock tubes are getting aged, or you are about to experiment some different tubes hopefully to improve the system sound to the better. Either way, it is a fun and exciting experience.

Please follow the steps below to change your tubes:

Step 1.: Confirm that your amp is working fine.

Sometimes you come to the point to buy new tubes because the amp somehow isn’t working properly. The issue could be the tubes currently in the amp are getting too aged; it could also be that the amp needs a re-conditioning in case resistor / capacitor are out of spec from aging. This is a very technical process – if you are not sure and cannot make an educated assessment from experience, talk with a tube amp service technician.

Step 2: Remove old tubes from the amplifier.

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My amp uses many tubes in total – which one should I upgrade?

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.

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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).

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.

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The confusion of Shuguang Treasure tube quality grade and price

The internet market place now has many vendors peddling the ‘black bottle’ Shuguang Treasure tubes at various prices for various grades. It has caused great confusion to consumers, if someone doesn’t want to take the time to read and understand about quality control and testing method to tubes.

Instead of answering the emails I have received one by one, here I will provide you the short answer when you see these descriptive words from a tube vendor:

Luxury, Gift Box, Premium = Export grade for western market = Expensive

For this quality grade, on the factory test card, you will see a small sticker like the picture below (if you don’t read Chinese, just think it as a picture -compare the first character to see if yours are the real Premium grade at least on paper):

Normal, paper box, Standard = so-so grade (these tubes light up and make sound, don’t expect too much more beyond that, but factory wouldn’t throw them in the garbage) = Cheap

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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.

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:

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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.

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.

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Why Grade A tubes only have one test card in the box?

We provide Grant Fidelity Grade A matched pair or quad of tubes – these tubes are usually packed in one box with one test card showing the ‘plate current’ reading in ‘mA’

Some customers inquire why we are not providing 2 or 4 cards showing same readings on all tubes – the reason is: we match tubes in pairs or quads to our specification. No two tubes will have 100% identical reading so we provide the average readings of all matched tubes in the package. It is misleading and untruthful to provide you 2 or 4 cards showing all same readings on all tubes because they simply DO NOT have 100% the same readings.

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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.

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.

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What’s the sound when I turn on the tubes?

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.

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Why my tube box isn’t in perfect shape?

Well, we audiophiles live on perfection but sometimes it’s hard to achieve. We make every efforts to make our tubes as high quality as we can, but sometimes the tube package boxes get damaged in wholesale shipping due to rough handling.

We do not stock extra boxes in warehouses as all tubes are air shipped from factory. Shipping an empty box will cost the same as we ship a box with products in it. To maintain cost effective on all products, we try to eliminate the unnecessary expenses and use the funds to source great products for audiophiles.

If you get a tube box with latch missing or slight wear and tear, we ask your kind understanding of the international shipping challenges and we hope to service you better next time.

We never cut corners on tube quality, but sometimes the box corners might be cut unintentionally 🙂 Thank you for your kind understanding.

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