28-06-2017, 01:01 PM
Yes, it took them a while to sort out plastic encapsulations. I'm looking at a HP334A at the moment (thanks, Andy 
) that uses a mix of metal and plastic, and most of the plastic types have hairy legs! I'm not sure what exactly I'm seeing - I'll get the USB microscope out when I have more time - but so far, they all seem to be working OK, so it's hopefully something benign that hasn't made its way into the plastic yet.
Also, I'm looking at a HP1740A with numerous faults - all caused by 'jellybean' 2N3904/6 types. No visible signs of distress, and no obvious electrical reasons for their demise. This 'scope is mid/late '70s, so you'd think we'd be past the teething troubles by now. Similarly, the MPS6518 - as used by Telequipment in the '70s - seems to fail for no reason too.
The Lockfit types did seem to get more reliable as time went by. Ignoring the high-powered (relatively) ones used for audio outputs, I don't recall failures in them post the mid-'70s. But it seems that as mass-production geared up to deal with TO92s on a bandoleer, there was no need for the Lockfit package any more.
Overall, "assume nothing" has to be the mantra... Luckily, it's pretty easy to test most transistors in-situ by observing what is going on around them - or at least it is with experience and understanding. There's no better transistor tester than the circuit it's installed in
) that uses a mix of metal and plastic, and most of the plastic types have hairy legs! I'm not sure what exactly I'm seeing - I'll get the USB microscope out when I have more time - but so far, they all seem to be working OK, so it's hopefully something benign that hasn't made its way into the plastic yet.Also, I'm looking at a HP1740A with numerous faults - all caused by 'jellybean' 2N3904/6 types. No visible signs of distress, and no obvious electrical reasons for their demise. This 'scope is mid/late '70s, so you'd think we'd be past the teething troubles by now. Similarly, the MPS6518 - as used by Telequipment in the '70s - seems to fail for no reason too.
The Lockfit types did seem to get more reliable as time went by. Ignoring the high-powered (relatively) ones used for audio outputs, I don't recall failures in them post the mid-'70s. But it seems that as mass-production geared up to deal with TO92s on a bandoleer, there was no need for the Lockfit package any more.
Overall, "assume nothing" has to be the mantra... Luckily, it's pretty easy to test most transistors in-situ by observing what is going on around them - or at least it is with experience and understanding. There's no better transistor tester than the circuit it's installed in
