How to select a good set of vacuum tubes?

• First, the appearance of screening
  

1. The glass bulb is clean, transparent and crack-free.
   
2. The core column is vertical, no shaking when shaking, no abnormal sound.
   
3. The glass bulb is well integrated with the tube base, no looseness.
   
4. the pins are smooth and not loose.
   
5. The tube’s diameter and height of the paired tubes are basically the same.
   

• Second, vacuum tube stability screening
  

Use Amplitrex AT1000 system, which can can quickly detect unstable products. For the unstable products,it will carry out the second burn-in, if it is still unstable after the second burn-in,these products will be identified as non-conforming products.

• Third, vacuum tube plate current screening
  

After the vacuum tube is completed, it cannot be repaired. In order to improve the product’s pass rate and economic benefits, the manufacturer’s plate current range is relatively loose. Take the ordinary KT88 as an example，under the manufacturer’s test standard, the allowable plate current range of the manufacturer is 20-70mA. In order to obtain a vacuum tube with a strong launching capability and a longer service life, we will place orders above the standard price for select a product with a plate current ranging from 35 to 60mA.

• Fourth, pairing screening
  

The tubes that entered the pairing process have passed the screening of the previous three steps. Our tube matching is divided into two levels:

FQ level: plate current pairing, the pairing standard is consistent with the factory. (We use this kind of matching method by default)

PQ level: plate current + transconductance pairing, paired product plate current error Ia < 5%, transconductance GM < 5%. This level of matching products needs to be booked in advance and an additional handling fee will be charged usd 5.0 / pc.