I wouldn’t have believed…

from William W.

I received a pair of your new copper foil caps (.22uF) yesterday and immediately installed them in my Yamamoto 45 amp as a coupling cap between the driver and power tubes. They are already remarkable after a few hours burn-in. I wouldn’t have believed how much they improve this wonderful amp. –William W

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:

  • 125 Premium factory tested tubes
  • 79 Premium Grade A  – 63%
  • 46 B stock  – 37%

Test results: https://docs.google.com/fileview?id=0B06Slh1HJxoKZDI5ZTMzNjktMWRmYS00NDQ2LTkxMDMtNWI0YTFjODg3Zjhm&hl=en

Shuguang Treasure CV181-Z (6SN7):

  • 107 Premium factory tested tubes
  • 58 Premium Grade A – 54%
  • 49 B stock – 46%

Test Results: https://docs.google.com/fileview?id=0B06Slh1HJxoKM2JkMWYwOWYtYTA5ZS00NzY1LTk2YzAtZGY5YjFjZGIxMjQz&hl=en

Shuguang Treasure KT88-Z:

  • 164 Premium factory tested tubes
  • 119 Premium Grade A – 73%
  • 45 B stock – 27%

Test results: https://docs.google.com/fileview?id=0B06Slh1HJxoKYTVmYTZiN2QtMDJhNS00ZmU4LTk1NzEtMGQzZTA2ZTlkMjky&hl=en

Shuguang Treasure 6CA7-Z:

  • 99 Premium factory tested tubes
  • 61 Premium Grade A – 62%
  • 38 B stock – 38%

Test results: https://docs.google.com/fileview?id=0B06Slh1HJxoKMDYwNzU4ZmMtYTcyMS00Y2EyLTk3NmUtZTRjMTAxOTVmYjJj&hl=en

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.

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.

How is 845 like when dead?

Some forum members had a shorted tube – here is a picture of how it looks like (credit to AudiogoN member ‘amfibius’) when the event happens:

Here are some explanation from Psvane tube engineer about the event:

1. The short (lighting show you have seen) on 845 tubes is caused by residual air in the vacuum tubes act with active materials on the cathode. When active materials (electron emission coating on the cathode) become detached from the cathode under extreme heat (1000V), it will act with the residual air in the tube causing a short (lightening arc). The residual air may not be present at factory final testing when the tube leaves factory, but during shipping/handling/or usage with time, very tiny amount of air could leak into the tube, especially these large sized vacuum tubes.

2. Very few tube factory still make 845 tubes nowadays – as far as I know, only Shuguang in China and KR Audio in Europe. KR 845 tubes have quality problems too such as red plate caused by over current, so Shuguang 845 tubes have been used on most modern 845 tube amps. Shuguang made a few different design 845 tubes in the past – including a metal plate 845C. The metal plate 845C tubes were considered best sounding among all past models but the metal plate soldering cannot handle extreme heat well, so historically there have been very high percentage failure rate (nearly 50%) so the metal plate 845C tube has disappeared from the market now.

3. When a 845 tube has an internal short, it will produce crackling noise to the speakers, but such a noise (if the amp volume was not extremely high) usually is not of extreme frequency and will not damage the speakers, but it could cause panic to the users when seeing the lightening and sound at tube failure. In an event of tube short, the amp’s main fuse will be blown to protect the main transformers in less than a second, so usually the amplifier will continue operate fine and no other parts will be burnt. The tube short happens internally in the glass enclosure – the internal pressure will never be more than air pressure in the environment because tubes are vacuumed (less air pressure inside than outside even a leakage), there will never be a glass explosion happening at the event. When too much air has leaked into the tube, the silver coating inside the tube will turn grey or white indicating the tube is no longer vacuum sealed, ie not usable anymore.

4. This tube failure event is unpredictable – but it’s not to be scared. Other type of power output tubes such KT88 and 300B do not operate at as high voltage as 845 (450V vs. 900-1000V), so consumers rarely see tube failure as often with those tubes as with 845. Once a 845 has a short (light show and sound), do not use it again in other amps – such a tube should be disposed.

5. NOS RCA 845 tubes are considered the best quality on the market, but the technology then has been somehow lost with time. Shuguang is continuing research and improving on their 845 tubes, but that will take sometime to become reality.

I hope this helps 845 tube users who have been ‘shocked’ by the lighting show 🙂 Not to be scared when the lighting happens – you have just witnessed nature at work from a close distance inside a glass tube.

Happy listening.

Rachel @ Grant Fidelity