Hi again Mike

?I agree with your comments, and was not suggesting that you said anything wrong, but I was hoping for some response to my previous comment/question on why did the “switch” trip due to a simple bulb failure?? Was it intentionally designed to do that, or an oversight, or accepted as an unlikely event that had a tolerable probability of not happening. I know we can’t generate any solid answer to the question, but we can think about it.?? However, if we do not know all the design criteria of something, it is tough to predict all the failure mechanisms, and so might be very tough to find a problem.

??

When I said “fusing”, I felt awkward, I really meant over-current? protection.

?

It would seem that most military equipment needs to be tough, and fuses can easily fail and can’t be reset, so are likely not allowed in this equipment, and many [mechanical] circuit breakers can be jarred open by a sudden impact, so can be difficult to produce.?? as an aside the tripping mechanism is/was highly sensitive in older 600 volt power? switchgear, which is certainly not what? we have been speaking of in here.? But one wonders, if we use a spring loaded mechanical contact with some mechanical “trigger PIN?” to release the spring,? just how many G’s can it take before it trips itself.? They must have made some special designs.?

?

But, all this is off the point of the real question that you first raised about a few guys not finding the simple problem.? I can sympathize with their dilemma.

?

I say: things need to be designed to allow reasonably easy repair, or, as now, throw out, and buy new.

We should be talking about the original question of what happens when bulbs fail?? I suggest there is more than one answer, all depending on the surrounding circuitry, and, in addition, when the “bulb”? becomes? a LED the question has to be re-evaluated.

?

Sorry for wandering around all this.

Don ?VA3DRL

?

?

?

Hey Don,

?

Please do not get me wrong, I agree with your assessment, curiosity and what you have experienced in other similar situations.? I was just pointing out that most everyone was taught that there is no such thing as a shorted lightbulb as the filament leads will end up burning themselves out thus eliminating any dead short that may have been initially incurred.? But when deployed in the right circuit design, or maybe an improper circuit design, it is possible that the filament leads will not experience enough amperage draw to burn themselves out before some other component or subsystem decides enough is enough.

?

The issue with fusing any specific circuit in that radio is that an RT-524 is a Military FM Transceiver. Its design was such that it was sealed from the weather as well as designed with minimal external user controls on the faceplate to operate the radio.? It had to be simple to operate for the user and be reliable in all kinds of weather and operating conditions.? It also definitely had to be rugged enough to withstand being slammed around by the user in varying combat vehicles. So there were no external facing fuse holders, and the user was not allowed inside of the transceiver, hence just the heavy duty external power switch that was user resettable.

?

Thank you,

?

Mike

W5CUL

?

?

Hi Mike

I guess you are commenting on my first? stuff .

I suggest that our ?typical room lights blow to oblivion, ?partly because they are protected only by a 15 amp breaker or fuse in the main panel of a house, and this allows a very high, short time current to ?burn up any shorting material in the bulb.

?

In the case of the RT-524 ?I can only guess that it also has a power transformer that will limit the short circuit current to the bulb giving the

more sensitive ?power switch/ breaker ?time to ?completely open ?the circuit, before the bulb blows.

?

This leaves the age old question to fuse or not and where… has a very long answer.

Don ?VA3DRL

????==== ??I trimmed a bunch, so the original situation??? is ?only in some previous posting? --- don

?

?

?

?