Thread: Sheesh
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legg legg is offline
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Default Sheesh

On Sat, 27 Feb 2021 12:27:16 -0800 (PST), "

On Saturday, February 27, 2021 at 12:42:20 PM UTC-5, wrote:
Lately I work on audio and have long thought that I get the **** that has already been gone through but I think I have ALMOST seen it all.

This amp in a receiver, not the greatest but is vintage, whatever it needed outputs though I don't know why.

So it is offset bigtime. The problem ? A 27K going to the emitters of the diff pair. So with that replaced it centers the voltage and all it supposeedly well but it has distortion. Wracked my brain or a bit and I decided to go inoto detail mode. What do I find ?

An 2.2K ohm resistor where an 18 ohm belongs. What's more it looked like it had never been changed or if so it was a very long time ago because the connections had the same dust on them as the rest of it.

**** like this is not normal, and I am dealing with more and more of it.

Then there is this quad unit, outputs good but it had more bad transistors than you could sweep off the floor. get the amp fixed and a channel is cutting out. Bad connection ? Nope, a transistor. Got that fixed and now off to another board that is no doubt full of bad transistors.

Life is trip, think of the destination.

The only time I really remember transistors being a red flag (other than early Germaniums) were some small Hitachi signal transistors from the 70s-80s - the TO-92 ones with the beveled top. Those things would go leaky or open or intermittent (their choice). It got to the point back then that I just automatically changed them whenever I saw one in anything I worked on. Pretty much eliminated any rechecks.

We had an issue with parts in TO98, which was a common package for
early GE plastic signal transistors. 2N339x 2n34xx. These were
encapsulated off-shore, possibly even a simple rebrand.

At the time, there was a suspicion that they weren't normal
supply chain product, as the bad parts were purchased through

Although conforming to TO98 outline, they were a filled-epoxy
package, vs a molded epoxy. Anything showing up with the
filled-epoxy construction was simply dumped at incoming
inspection. Rubbish.