We only carry Chinese vacuum tubes and we only carry the best. There are two testing methods used on all tubes we sell.
1. GF (Grant Fidelity) Test Method
2. Factory Test Method
About GF (Grant Fidelity) Test Method:
Grant Fidelity (GF) Test Method is a unique after-production test method we use on high end tubes we sell, which includes 5 steps on 5-specs:
1) Starting before factory shipping, we stipulate our acceptable plate current tolerance to factory, which is no more than 20% from the nominal published specification from the factory ).
All tubes from the production run are divided to either Premium Grade or Standard Grade by the factory, who will pick out our orders from their Premium Grade inventory according to our specification tolerance to fulfill Grant Fidelity orders. From each production run of high end tubes, typically only a small percentage of tubes are in our stipulated specification range. Rest could vary from nominal specification up to 40% or even more.
2) Once the factory rated Premium Grade tubes, a further testing is conducted on every tube to ensure no visible defects. Please note that the shape of glass enclosure is NOT considered a defect as this is a manual process – no two tubes will be 100% identical.
3) All tubes are then further tested on the industry’s most advanced computerized electron tube testing system – Amplitrex AT1000 tube tester, for all 5 specs: Plate current, Transconductance, Heater-to-Cathode Leakage, Internal Gas and Microphonic. Amplitrex test tubes at real working voltage except for high voltage tubes such as 845/211/805 (the maximum voltage a tester can get to is 500V). Remember factory method only tests plate current in their factory QC process; Grant Fidelity testing method tests all 5.
4) All tubes that went through the Amplitrex test are then further graded according to the 5-spec test results to either A, B or Clearance grade. Top quality grade A matching will be well within 10% – in many cases less than 5%. This is usually a much closer matching than the factory matching method and all tubes with inferior specs on other parameters will be screened off.
5) Any tubes that have failed any of Grant Fidelity 5-spec test will be rejected back to factory. We no longer offer B grade or clearance grade since 2011 as we now conduct Grant Fidelity testing method right at the factory before tubes leave for shipping.
Depending on factory’s QC control at production, from each tube production run the proportion of GF Grade A quality varies from time to time. However, our grading standard stays the same all the time.
Grade A tubes are the best quality Grade we carry and they will last longer than an inferior grade tube. They will also perform better in a live circuit due to its superior electronic parameters. Grade A tubes are sold at premium price, for its quality, rarity and longevity.
The above Grant Fidelity tube testing method are now used on all GF tube orders before tubes leave factory warehouse to reduce the percentage of low grade tubes we receive. Grade A tubes can be shipped at a given time from either our Canadian warehouse or Hong Kong warehouse with same quality commitment from us.
About Factory Test Method
This refers to the standard production quality control method used at tube factory. If a tube is sold as factory tested only, it has not been tested under GF Test Method.
From our testing experience, quality of factory tested and matched tubes varies. These tubes are sold for lower price than GF Grade A tubes, because only a small percentage of them meet our GF Grade A standard.