What is this?

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Fintek

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I recently have been given a bunch of components from an old tv repair shop. These were included, any idea what they are?
I thought they were some optical sensor, but there is no openings, and also no continuity between the leads.
 
those look like "bias stacks" used in older stereo amplifiers.... there's 3 or 4 diodes in series in them, and the device mounts on the heat sink between the output transistors to thermally compensate the bias voltage on the output devices and keep the idle current within safe limits.
 
Must admit I've NEVER seen any such device, despite spending 46 years repairing domestic electronics.

As unclejed suggests, they 'could' be for bias compensation, but I've never seen anything like them used in that way.

Easy to tell though - if they are multiple diodes you can easily check them with a power source (9V battery) and a series resistor.

Personally, I've never liked the idea of diodes or thermistors as bias compensation, and would always use the nicely adjustable Vbe multiplier design, which also tracks better, being a transistor.
 
Rather common used on many of the legacy Pro Amplifiers such as Pioneer SPEC2 and others....
STV4H & STV3H were the common part numbers in the U package. Basically a 3 or 4 diode array used for thermal biasing fastened to the heatsink.
The biggest drawback of the device was the eventual corrosion of the connecting wires mainly at the base of the package and were finally discontinued.
 
I checked it with a multimeter on diode check and it showed open, but with my component tester it identified as a diode. Weird. I've never seen any of these before. Learn something new every day!
Thanks for the solution!
 
Fintek said:
I checked it with a multimeter on diode check and it showed open, but with my component tester it identified as a diode. Weird. I've never seen any of these before. Learn something new every day!
Thanks for the solution!
Click to expand...
Two questions:
Have you considered the polarity when in diode test mode?
What Vf you got?
 
Yes, I flipped it and checked both directions. I think unclejed613 had the right answer since Vf is 1.90 v.
If it's multiple diodes in series the multimeter I used may not have figured out out, it is a cheapo one I had at work.
 
Fintek said:
Yes, I flipped it and checked both directions. I think unclejed613 had the right answer since Vf is 1.90 v.
If it's multiple diodes in series the multimeter I used may not have figured out out, it is a cheapo one I had at work.
Click to expand...

Probably doesn't matter if it's a cheap meter or not, they aren't generally designed to test multiple diodes in series, so are unlikely to check these - as I explained in post #3 they are trivial to check though. If you have an old Avo8 meter you could check them on the high ohms range though, as that used a 15V battery - also assuming you have a battery in it?.

Best thing is to sell them - they are long obsolete, and in demand by people repairing the few old amplifiers that used them - so you could probably get good money for them.
 
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