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Texas star dx 350 staying hot when off?

I'd feel better if I knew where the transistors' base current is coming from. The relay is in charge of that current source. If the relay is failing to shut it down in receive mode, that's one kind of problem. And it the relay is not at fault, some other unwanted connection is feeding juice into the bias resistors when it shouldn't.

73
 
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I think you guys might be going a bit over OP's head.

How about an experiment rflegacy?

do you have a second radio to listen on?

if so, turn it on and set it to the same channel your main radio with the amp is set to.

put the second radio close enough to your vehicle and with enough of an antenna (piece of wire?) that it will pick up the signal from your other radio/amp.

now key the mic of your main radio with the amp on, and note the signal it produces in the other radio.

now unkey the mic.

is that signal still there in the second radio?

if so, remove the power from the back of the amp completely.

now did the signal go away?

report back with your findings.
LC
 
Figured it out finally after wasting time with all the original bad suggestions. A simple diode test on collector and emitter on pills showed both were shorted witch was causing my drain. New HG pills and we got fire in da wire now.
 
Couldn't have been "shorted"
One spec for bipolar transistors frequently overlooked is the reverse-bias "leakage" current from collector to base. If you look at just those two terminals of the transistor, you have a reverse-biased diode. All diodes have some amount of reverse-bias leakage current. This spec for a 2SC2879 is really small. Primitive transistors from 60 years ago would have enough of this leakage current to keep you from shutting them off properly. When the industry changed from germanium transistors to silicon this problem became a lot more rare. A 2SC2879 is actually a dozen separate transistors all in parallel. If one of them breaks down between collector and base, the current coming out of that base terminal will 'turn on' the other eleven transistors in parallel with it.

Pretty sure I have seen this at least once in the last 47 years.

But not often.

73
 
On the 14th post, someone suggested reverse leakage. Not bad for a one in 47 year problem in my opinion. Especially for a group of people that are trying to find the problem without even looking at the amplifier. The op didn't find the reverse leakage until post 33, but at least he found it. And I am sure that other people learned something along the way, I know that I did. That's why I keep coming back, but to each their own.
 
Figured it out finally after wasting time with all the original bad suggestions. A simple diode test on collector and emitter on pills showed both were shorted witch was causing my drain. New HG pills and we got fire in da wire now.
And that also gets back to my suggestion of checking the bias resistance and bias voltage as the first step. The issue would have shown up then at the beginning, and then followup with testing the transistors.
Would have saved the OP a bunch of time.
Bias checks is always my first step in checking these types of amplifiers.
 
Couldn't have been "shorted" or it would have blown breakers/fuses. Looks like my suggestion of massive reverse leakage was correct. I guess "all" of the suggestions weren't bad.
When an Emitter and collector are shorted, the transistor cease to work as a switch. Basically, the electrons from Emitter to reach Collector by bias and hence it becomes switch. Now you have shorted, both ends of the switch its basic function as switch is defeated. Am I wrong?
 

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