NTE Electronics NTE181 NPN Silicon Power Transistor, High Power Audio Amplifier, 100V, 30 Amp

Works well under load

Well, let's see .... I needed some replacements for a couple of RCA BA-74 Monitor Amplifiers (you want what??? those haven't been made in must be 40 years!), the original being RCA 40411. I ordered, they arrived. Price was .... well ..... let's call it reasonable. Since this is a review of the product, I'll describe what I received. Spec: Transistors. Yep, that's what they were. Spec: TO-3. Yep, TO-3. Spec: NPN. Yep, I'm pretty sure they are. Spec: Silicon. I have to assume they are. Not quite feeling like taking one apart to do a chemical analysis.In any case, I was having an issue with one of the amplifiers. It would periodically go into a low-frequency pulsing sort of along the lines of motorboating. It would get bad enough to pop the line fuse. Holy crap, man! Why are fuses so expensive? I had already replaced all the electrolytics so I assumed I had screwed up and/or had a bad one. But on another amplifier I had a bad transistor that was heat-sensitive. So I ordered the NTE-181's since for some dumb reason the original 40411's are a bit difficult to find. The replacements arrived and I popped them in. As is my habit, I brought the line voltage up slowly and .... rats. The pulsing was still there.So, loyal readers, today's lesson is that one does not use the same techniques to service transistorized equipment as is used for vacuum tube stuff. Bringing up the voltage slowly is just freakin' dandy in case of gross overloads or shorts. But it doesn't do squat as far as circuit operation is concerned. The manual called for 50 volts coming out of the power supply. Mine was running about 42 volts. Close enough for lots of stuff, but not in this case. I decided to up the input voltage to get the 50 volts and make some serious, yet quick DC measurements, before fuses started popping again. Lo and behold, at 50 volts all problems went away. The amplifier amplified, and quite nicely. Hindsight (always 20-20) tells me the internal feedback paths really depend on the power supply voltage being dead on. That's when I found the power transformer was connected for 125 VAC line voltage. Re-connecting it for 115 VAC brought the power supply voltage up to where it should be (my line voltage is typically 118 or so, measured true rms).So, back to the product review- I decided to put the original 40411's back in to see if they were functional and they were. The NTE-181's now reside in my spares collection. Let me add this: each transistor is packed with a mica insulating washer and insulating washers for the base and emitter leads. Nice touch. You have to understand back in the alleged good ol' days these things had to be ordered separately. So I'm a happy camper.

Works