Bob Scott wrote:Dean Huster wrote:Jack Cox, K5TQM, lastly of Gulfport MS, now a silent key for many years, was my inspiration.
You use facinating diction. You should continue to be an author. If you don't, it's a waste of talent.
Dean Huster wrote:He had a Heathkit 20m xcvr he carried around with him.
I knew a guy who carried a portable CB everywhere he went. His glass was only half full, if you know what I mean.
Dean Huster wrote:I have a feeling that if I turned the T150A on, the electrolytics would wipe out the entire inside of the cabinet.
That's the second time that I've seen you say that electrolytics blow up when they get old. In my experience, they don't leak current. They just lose capacitance so that excessive ripple voltage appears on the DC supply. Keeping them hot, mounted very close to hot power dissipating parts (eg: TV Vertical output Xistor), accelerates the drying of the electrolyte; ages them faster. There is no boom unless wired in reverse polarity or excessive DCV is applied.
When I was a kid my Dad told me this: "It is not good for electrolytic caps to be uncharged for a long time, or used at too low a voltage. If a 600 V electrolytic cap is constantly used at 400V, it becomes a 400V capacitor."
I didn't know they would violently destroy themselves when charged after a long period of discharge.
Bob
Hey, I got caught up in the CB craze too, during the mid 70's to early 80's.
A friend got a vehicle mountable radio, and set it up with a 12V Nicad battery pack.
And adapted a scanner antenna for it.
It worked ok, thou, he could only get about 3 hours out of the batteries.
He could of gotten one of the hand held radios that Radio Shack sold.
But at the time, it was cheaper to build up his own portable CB setup.
{That and the vehicle units had more transmitting power.}
Well, as for old electrolytic capacitors.....
It is true that they can sometimes explode.
I should know, I've had enough of them pop on me.
On older equipment, as you say, tends to be do to heat drying them out.
But I have come across bunches of defective electrolytic capacitors.
{Especially ones that came from China.}
These were in SMPS in VCR's: GE, RCA, and a few other brands that used the same design of SMPS.
As for caps sitting on shelves for long periods of time.
Yeah, It isn't a good idea to place the electrolytic into a circuit without checking it first.
There is a method for reforming old electrolytic's.
But I've never tried it.
I've always replaced the defective electrolytic with a new one.
But I was always told that whenever powering up a old piece of equipment.
Put it on a variable isolated AC supply, and slowly bring the AC voltage up.
Watching the Amp meter in case the current starts to climb to high, indicating a shorted cap.
Thus, shutting it down before you do damage to it.
I had a little GE portable TV that came in for a electrolytic problem.
It was strange, The set had popped the 1.5A Fuse.
I replaced the fuse and slowly bought the power up to 110VAC.
It worked fine.
I shut off the set, and turned it on several times.
It seemed fine.
I then unplugged it, and put the back on the set.
I then plugged it back into the 110VAC.
I turned it on, I heard a faint pop, and the set was dead.
Opened it back up, here the fuse had popped again.
This time I grabbed a 1A circuit breaker and jumper it onto the fuse.
I slowly bought the power up to 110VAC.
The set came on and was working.
I unplug it from the AC Variac, going directly to the 110VAC again.
The set ran fine.
I then unplugged the set, and left it off for 5-10 minutes.
I then plugged it back in and tried it.
The circuit breaker popped right away.
Well, here's where things got interesting.
At the front end of the power supply.
Just after the full wave rectifier diodes, sits a 680uF 200Vdc electrolytic filter capacitor.
I did simple tests for leakage, with a hand held meter, but it showed it to be fine.
Well at the shop I had excess to a Z-Meter.
Boy do I wish I could of bought it when the shop closed.
The Z-meter shown that the electrolytic had very slight current leakage,
just enough to cause the cap to act the way it did.
I replaced that electrolytic, and then the set fine.
Now when I see a popped fuse on a set.
I now always check the electrolytic filter capacitor right away.
Signed: Janitor Tzap