EO Pulsar 1KW problem

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Joe Friday
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EO Pulsar 1KW problem

Post by Joe Friday » Wed Apr 12, 2017 8:33 pm

I look after a 1KW EO Pulsar that has a strange problem. In the exciter chassis, it will occasionally blow the 3A +15V fuse. It is a non-catastrophic failure, and the transmitter immediately returns to air following replacement of the blown fuse. Generally, it will run between 4-6 months between blown fuse events.

This chassis has some surge protection on both the +15V and -15V supplies, and this is what I suspect may be causing the problem. Just wondering if anyone else has had this issue in the past.

Thanks!

Kevin

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kkiddkkidd
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Re: EO Pulsar 1KW problem

Post by kkiddkkidd » Fri Apr 14, 2017 10:53 am

I looked after a 1kw Pulsar for several years and never had that problem. Is the fuse bad or blown? IE, filament just barely melted or really exploded. Can you check the normal current thru the fuse?

Later,
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Kevin C. Kidd CSRE/AMD
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KPJL FM
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Re: EO Pulsar 1KW problem

Post by KPJL FM » Mon Apr 17, 2017 7:20 am

Probably a flaky capacitor in the works. You might try hitting all of the small ones with a heat gun. Or freeze spray. Or wait for the inevitable.
Trim to fit, paint to match, tune for minimum smoke.

kcbooboo
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Re: EO Pulsar 1KW problem

Post by kcbooboo » Mon Apr 17, 2017 12:18 pm

Small tantalum caps (1-33uF) are well-known for intermittently arcing and shorting out, enough to blow fuses or bring power supplies down for the short count. Sometimes they take the resistor in series with the power rail (if the engineer designed the circuit properly) or the foil trace, in lieu thereof.

Bob M.

Joe Friday
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Re: EO Pulsar 1KW problem

Post by Joe Friday » Tue Apr 18, 2017 7:40 pm

Thanks for the responses. The failed fuses are always a non-catastrophic failure, just barley melted. I don't believe normal current draw is a problem, as I briefly replaced the 3A fuse with a 1A fuse, and the transmitter ran for about 5 minutes before I swapped it out for the proper size. At this point, I will probably do a shotgun recap on the chassis and see what effect it has on the issue. Other than this nagging problem, it has been surprisingly dependable, and sounds good on the air on a talk format with an old 9100 ahead of it. I have cared for it for 3 1/2 years. I have not ran the NRSC measurements, a traveling engineer has always done them.

Thanks again!

Kevin

rfn
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Re: EO Pulsar 1KW problem

Post by rfn » Wed Apr 19, 2017 2:05 pm

When I was young and reckless I'd "shotgun" components of similar age/type. Then, all too often, I'd spend days trying to figure out which new part was causing the more severe problems that resulted. Occasionally it would be something I had done wrong - more often a bad batch of parts. Worst was when, out of maybe twenty caps, two were bad-out-of-the-bag. Now that I'm old, gray, measuring my time left to me, I change one at a time and, if it works out, change one more.

But worst I ever had happen was when an even younger assistant completely re-tubed a geriatric Raytheon KTR-1000 (including klystron). Finally had to put back all the old tubes which were aging but not defunct and then start over one at a time.

Shotgunning might save you a little time but there's some chance it'll turn a repair into a career.

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Shane
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Re: EO Pulsar 1KW problem

Post by Shane » Fri Apr 21, 2017 3:09 pm

I'm aware of a 1960's Ampliphase where the engineer on duty decided to replace all the tubes in the exciter. He and the CE got to spend a few days getting it to work again. The guy's ears were still red 25 years later!
Mike Shane, CBRE
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kkiddkkidd
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Re: EO Pulsar 1KW problem

Post by kkiddkkidd » Sat Apr 22, 2017 7:40 pm

One my oldest clients nursed a Raytheon RA1000 far past it's useful life.

It was not unusual to get a panicked 6am call from the owner every couple of weeks telling me that one of the meters was down and he had replaced a tube but that didn't fix it and he replaced another and another and another. Most of the tubes for that rig became VERY EXPENSIVE toward the end. Not only were they expensive but they were junk. A good 33.3333% of new tubes were bad out of the box.

If I was around when the owner got a new batch of tubes, I would take them out of the shipping box and give them a good shake. About a quarter of them rattled and went back in the box with the getter floating around loose. The other 75% got tested in the tx and a fair portion of them put back in the box to be returned for poor emission.

The owner went by the TX at least 3 or 4 mornings per week before he signed on. The old RA1000 had meters on almost every stage and he would panic if one of them wasn't exactly right on the sharpie marks on the meter faces. After a couple dozen self-inflicted off air emergencies he finally started calling BEFORE swapping tubes around. I finally got across to him that if the base current was correct, it made 100% modulation and it sounded good, he shouldn't be screwing around with it.

There is no telling how many perfectly good tubes went in the garbage at that station due to paranoia...

Almost every transformer in the old rig (non-PCB) eventually started leaking and failed. That tx also tried to kill me one time.

They replaced it with a BE AM1A and I smiled.
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Kevin C. Kidd CSRE/AMD
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Tom Osenkowsky (RIP)
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Re: EO Pulsar 1KW problem

Post by Tom Osenkowsky (RIP) » Tue Apr 25, 2017 5:57 pm

Since you mention "melted" I would look at the fuse socket itself for signs of poor contact causing a heating condition. This has occurred in B.E. AM-5 transmitters, Excel tower light controllers and Crown 600E units. Resistance can cause heating between the holder and the fuse itself.

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kkiddkkidd
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Re: EO Pulsar 1KW problem

Post by kkiddkkidd » Tue Apr 25, 2017 6:09 pm

This was the point of my question several posts/tales earlier.

A bad fuse that is melted vs. a fuse that is violently blown are 2 completely different situations. A larger fuse IS NOT the answer either. If it is a fuse holder problem, the holder will probably melt loose and cause all manner of havoc...

In this case, measuring the current thru the fuse AND the fuse contact area temps after several hours of operation may reveal a marginal problem.

Later,

Tom Osenkowsky wrote:
Tue Apr 25, 2017 5:57 pm
Since you mention "melted" I would look at the fuse socket itself for signs of poor contact causing a heating condition. This has occurred in B.E. AM-5 transmitters, Excel tower light controllers and Crown 600E units. Resistance can cause heating between the holder and the fuse itself.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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