A couple months ago I pulled the blower fuse on an operating FM transmitter and it kept on transmitting. Simple PM check that's often not thought about. A simple calibration of the air flow switch and now it dumps when the fuse is pulled. Checked all of yours lately?
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Checked that airflow switch lately?
- Thread starter BobOnTheJob
- Start date
A BE 25 transmitter I service began doing extremely short (and random) shut downs that were caused by generic air filters that didn't have a strong enough backbones. The filter would flex onto the fan intake and restricted the airflow until the motor slowed enough to let the filter loose.
I fixed the problem by making a clip out of a large paper clip that held the filter's center area to the intake vent.
BTW, does anyone have a source for 15 3/8 X 19 3/8 X 1 (actual size) filters that are tough?
I fixed the problem by making a clip out of a large paper clip that held the filter's center area to the intake vent.
BTW, does anyone have a source for 15 3/8 X 19 3/8 X 1 (actual size) filters that are tough?
and if the owner has tied a little string to the air flow switch to make it work, something else is wrong and needs to be fixed.
I once serviced a Harris FM20K where the 4CX15000 was nearly black from overheating. Putting your hand over the exhaust would burn you. I was surprised this transmitter stayed on the air. Taking the blower assembly apart revealed that the squirrel cage was so encrusted with dirt that the individual vanes had completely lost their aerodynamic shape and were, basically flat. Scraping the dirt from the squirrel cage vanes resulted in a huge increase in airflow and reduced the stack temperature to reasonable. The staff complained that the transmitter was too noisy and said it hadn't made such a racket in years. I shuddered at the thought of that rig running for years in that condition and then I told them it's better to have the noise and be on the air.
Also, in the bottom of the assembly were four 4cx250B drivers. Apparently, it was the custom of someone in the past to lay the tubes on the deck but then they would bump them into the blower. The tubes all had multiple dings on them from being thrown around inside of the plenum. Surpriningly, two of them still worked fine.
Also, in the bottom of the assembly were four 4cx250B drivers. Apparently, it was the custom of someone in the past to lay the tubes on the deck but then they would bump them into the blower. The tubes all had multiple dings on them from being thrown around inside of the plenum. Surpriningly, two of them still worked fine.
I forgot to mention that the airflow switch did, indeed, work in this transmitter. Evidently, there was still just enough air pressure to keep the rig from shutting down. Probably, it would have been a good idea to adjust the switch, but we replaced the transmitter not long thereafter and it became the spare.
I once took a BRICK off the exhaust output of a 4KW CCA. The owner seemed to think that re-directing the air flow would reduce the chance of the air flow switch not staying in the ON position...I'll go to my grave puzzled over that logic. Amazingly, the tube looked shiny and new after a year of service.Bengalsfan said:
Best I have is the terminal breaking free of the airflow switch 45 mins before morning show and the morning guy freaking out on me to get it back on the air NOW... had to order the switch, could not find anything to work locally, that was the most nervous I've been for 24 hrs hoping a blower didn't fail with the switch bypassed.
Here just a week or so ago, had a transmitter randomly leaving the air just to come back 45 secs later. HV overload alarm every time, had me chasing my tail for a while until I realized upon looking that the filaments were dropping when this happened. Opened it up to find a plugged screen in the exhaust letting just enough air through to barely engage the switch and it would sometimes drop back, killing filaments and tripping the HV overload.
I'm still not sure how it got that dirty that quick, had not been long since it was cleaned...
Here just a week or so ago, had a transmitter randomly leaving the air just to come back 45 secs later. HV overload alarm every time, had me chasing my tail for a while until I realized upon looking that the filaments were dropping when this happened. Opened it up to find a plugged screen in the exhaust letting just enough air through to barely engage the switch and it would sometimes drop back, killing filaments and tripping the HV overload.
I'm still not sure how it got that dirty that quick, had not been long since it was cleaned...
That's one way to confirm that the air flow switch was working properly!stephend2 said:
A working airlow switch didn't help when the filiment contactor on the GE 4BT50A welds itself on. Had to dismantle it and pry it open.
Even though one phase of the 480 was missing, most of the tubes didn't survive. It was back on the air in a couple hours.
Even though one phase of the 480 was missing, most of the tubes didn't survive. It was back on the air in a couple hours.
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