When restoring audio amplifiers, the rule of thumb is that whenever you come across transistors that look like outhouses, replace them with new ones. Is this something that is followed with CB radios as well?
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Do you guys change outhouse transistors?
- Thread starter PoDuck
- Start date
Only if they have a crescent above their door . . .
But seriously; I would be far more concerned about all of those very old caps.
But seriously; I would be far more concerned about all of those very old caps.
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poduck,
I remember this being a big deal with the 2SC458 transistors used often back in the day.
What i can't remember is whether or not that 'rule' was just applied to other transistors that looked similar, or if other transistors degraded in the same way the 458's did.
I don't ever remember a CB tech talking about doing this, so i'm going to say no it's not something that is being done regularly.
LC
I remember this being a big deal with the 2SC458 transistors used often back in the day.
What i can't remember is whether or not that 'rule' was just applied to other transistors that looked similar, or if other transistors degraded in the same way the 458's did.
I don't ever remember a CB tech talking about doing this, so i'm going to say no it's not something that is being done regularly.
LC
I would do a signal trace with an oscilloscope and as long as the signal looks good I would leave it alone. When I worked at Motorola there was a thing called lead dress. You would have to route the wires in a particular fashion and certain components were shoved together, separated, wire set between other components. This was done to bring sometimes marginal radios into compliance.
That transistor pushed forward could be a part of that process.
That transistor pushed forward could be a part of that process.
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Most of these are 2sc458 transistors. It's not a big deal, as I have tons of KSC1845 transistors to replace them. These others I'm not sure about though, and although I'm not finding any 2sc458s handling anything that gives a frequency, I am finding others that look like them, and what I was told years ago was, "Whenever you see a transistor shaped like a shit house, replace it, because all you get from a shit house is shit." He didn't care what part number it was.
I just don't remember anyone speaking of them in CB circles, but it's everywhere when it comes to audio. I was initially having audio problems, but now the caps have been replaced, the audio is fine. I am having frequency drift problems though, and I am looking suspiciously at these outhouse caps.
Believe it or not, all those old caps are Nichicon and Nippon Chemicon, and I only found one that tested out of spec, and all the rest had decent ESR, but I replaced them all anyway. Usually, in a radio this age, I will find at least 5 that are dead or out of spec.
Replacing them because someone thinks they look like a shithouse and all you get is shit from them sounds like a make work project based on ignorance to me. Just saying.
What's that old saying ..... " If it ain't broke don't fix it " ?? 
I've see seen what these do when they fail, and they often fail strangely. For instance, I recently had a problem with a Marantz amplifier, where it presented multiple different symptoms. It would start out playing fine, then it would start clipping more and more, until I was only getting the negative side of the waveform. If I turned the volume up, it would sound scratchy, as though there were a dirty potentiometer, even though the potentiometers are absolutely clean. The gradual nature of the clipping usually suggests a capacitor, since it would build up over time, and go away after allowed to rest, and it was even impervious to freeze spray on the transistors. I had replaced all the aluminium electrolytic capacitors though, so I then replaced the tantalum capacitors, with no effect. I removed the transistors and tested them with a transistor tester before I replaced capacitors, and all tested fine, but I decided to remove them once more, after replacing all the tantalum caps, and test them on a curve tracer, and two of them were bad.
They will appear good, and even test good with your average tester, and will present symptoms not normally associated with transistors, but actually be bad, and the only way to test them properly is with expensive equipment most people don't have, and given how cheap their replacements are, are more cost effective to replace than to test.
They will appear good, and even test good with your average tester, and will present symptoms not normally associated with transistors, but actually be bad, and the only way to test them properly is with expensive equipment most people don't have, and given how cheap their replacements are, are more cost effective to replace than to test.
Found the bad transistor, and it was a 2SC460 that was bad. Replaced it with a KSC1845, and all is well with the frequency stability. Now to do an alignment, and call this one done.
I'm going to bet that the squelch problem on the other radio is one of these transistors as well.
If this were a more valuable radio, I would be replacing all of them. They tend to go bad over time, and not based on use, like electrolytics, and these things are approaching 40 years old. Plus, there are only about 10 of them on this board.
I'm going to bet that the squelch problem on the other radio is one of these transistors as well.
If this were a more valuable radio, I would be replacing all of them. They tend to go bad over time, and not based on use, like electrolytics, and these things are approaching 40 years old. Plus, there are only about 10 of them on this board.
If it ain't broke, keep fixing it until it is.What's that old saying ..... " If it ain't broke don't fix it " ??
Are they Hitachi?
The bad ones are Hitachi, Fairchilds are ok
good reading here:
http://www.tapeheads.net/showthread.php?t=64534
if they are hitachi, they should be replaced
KSC1845 is the best choice
The bad ones are Hitachi, Fairchilds are ok
good reading here:
http://www.tapeheads.net/showthread.php?t=64534
if they are hitachi, they should be replaced
KSC1845 is the best choice
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If it aint broke yet,your not trying hard enough
