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Are all tubes created equal?

Disclaimer: The following comments are specifically related to Chinese tubes based on Grant Fidelity's hands-on experience through factory tours and reselling vacuum tubes made-in-China. 

1. How are tubes are made? 

Vacuum tube making is a highly labor intensive manual process. Like any handcrafts, it's next to impossible to have 2 vacuum tubes 100% identical. To see the tube making process, visit Shuguang with Steven Rochlin, editor of EnjoytheMusic.com on his Dec 2009 factory tour: http://www.enjoythemusic.com/china_2009/shuguang/

2. What type equipment is used in making vacuum tubes? 

Instead of diving into technicality and confuse everyone, I have a short answer here - vacuum tubes are typically made with the same equipment that tube manufacturers used in the 1950's. This is a boutique industry that has maintained the old time charm. Shuguang has modernized some manufacturing process such as enhanced vacuuming process by much larger scale self-designed new equipment. However, the overall manufacturing process of a vacuum tube doesn't changed much from decades ago. In 2008, Shuguang launched their new Treasure series which has 60 extra steps in production for making the 'black bottle' tubes. 

3. How is quality control done in vacuum tube production? 

Please note this question is about QC during production. All parts going into a vacuum tube are pre-selected through testing and visual inspection. The glass enclosure is also screened for proper shape and strength. After each installation step, the work-in-process vacuum tubes are further examined at various quality control stations in the factory. 

4. How is quality control done in vacuum tube distribution and retail? 

Step 1: QC at factory: 

A well-made vacuum tube needs to be burned in and further tested before it is ready for sale from the factory. Shuguang conduct burn-in on all tubes when they are off the production line. After burn-in, the tubes are tested at the factory and matched according to "plate current" with industrial equipment which will be calibrated every two months. Factory tube testing results have some inherent statistical error due to the time from equipment calibration. Test results obtained right after equipment calibration are tend to be more accurate then those obtained close to the next calibration. 

Chinese tube manufacturers typically only measure plate current at the factory QC process. At Shuguang, microphonics, transconductance, heater-to-cathode leakage and internal gas are not numerically tested in the production or QC process. These parameters are "controlled" by the manufacturing process but are not "measured" with a test equipment. Logically there will be some tubes with inferior or even failing results on these untested parameters will end up into distribution as if they are quality tubes. These are the 'lemons' covered by Shuguang manufacturer warranty which typically lasts 6 months from the factory shipping date. 

Shuguang historically select the tubes with better plate current test results for its export market. These tubes are sold as "Premium Grade" with higher price and tend to work closer to the tube's designed specification and has a longer lift span. Weaker tubes are sold mostly within Greater China (including Hong Kong and Taiwan) with lower price for domestic consumers to match local affordability. 

For the Shuguang Treasure series: 

Premium Grade tubes such as the Treasure series are usually packed in nicer packaging as shown in the left picture below for international shipping and handling. Standard Grade tubes are packed in paper box (right side picture) which costs less to ship around but tubes are less protected. Premium tubes with nicer packaging also tend to have better resale value. 

            

 

Shuguang DOES NOT make any special mark on their Premium tubes so it's not possible for consumers to tell which tubes are Premium Grade and which ones are Standard Grade, once the tubes are out of the original packaging. This is something Shuguang has to work on to ensure that Standard Grade tubes are not sold as Premium Grade by unethical resellers. Before any marks are applied to the Treasure tubes, consumers must be cautious about their purchase sources. 

Step 2: QC at Distribution

Once vacuum tubes are sold to a distributor or reseller, the tubes have to be shipped from factory warehouse to the reseller's location. Tubes are extremely fragile - excessive shock, drop or mis-handling during this shipping process could result in internal damages to the tubes which are invisible to human eyes but can be detected by sophisticated vacuum tube testing equipment. This detecting process is called 'QC at distribution'. 

This 2nd step QC is only carried out by some resellers but not all. Individual tube re-sellers on eBay are very unlikely to have a sophisticated tube testing equipment to confirm the tubes are still in factory condition after the shipping process, so the so-called 'factory tested and matched' claim in the listings is really irrelevant to consumers at this point of time since you have no idea if any internal damages have happened up to this point of time to the tubes you are buying. There is a high risk of receiving a tube DOA ("Dead on arrival") from this type of straightforward resellers. They add no value to the tube distribution except listing the product and collecting money before shipping. 

Some commercial tube resellers do apply some QC once they receive factory shipment. However, some commercial sellers only have outdated tube testing equipment that is made in the 1940s-1950s which can only tell a tube is functional or not, but not for exact matching, leakage or excessive internal gas testing. When a consumer purchase high end tubes from these type of resellers, the buyer has to rely on the factory test result - which as mentioned above, is subject to inherent errors from the industrial equipment used. 

 

Read on: Grant Fidelity 5-Step 5-Spec QC at distribution on Shuguang Treasure tubes 

"What sets Grant Fidelity apart from other tube resellers"