It has been mentioned previously that Germanium transistors are failing due to low current gain (HFE), now I see the same thing is happening to first and second generation Texas Instruments NPN silicon devices.  Some J213, 2N264 and 2N1150 have gains well below published levels and also have high leakage currents.

I am using the handy, dandy Multi-function Tester, TC-1 to check transistor current and HFE.  Some have have emitter currents 10 times higher then that of other devices tested.  I am not sure if 6mA is the current limit of the CT-1 or not but that is about the highest current seen so far.  The transistor leads were unsoldered form the circuit board before measurements were made so I am pretty sure that the problem is internal to the DUT.  

It is getting hard to find modern devices with a HFE around 30 or so to better match the devices being replaced.   Been using TI house numbered devices as replacements after sorting out devices with a HFE above 40.  To keep circuit changes to a minimum, I have resorted to removing emitter resistor bypass caps to keep the circuit gain in check. 

Perhaps the boards I am repairing are the worst of the worst since I have also found a shorted mica capacitor which took quite a while to find.  Interesting that perhaps a dozen transistors have been replaced so far but only one subminiature tube needed replacement.  It was still functional but had heater-cathode leakage which put 60 cycle modulation on the plate signal.

Happy Holidays, 

Jim