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 Post subject: PRC-47 Transmit issues.
PostPosted: Feb Sun 04, 2018 5:30 pm 
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Joined: Mar Thu 15, 2012 10:28 pm
Posts: 60
I posted about this transceiver when I first got it. I was looking for pinouts for the U-77 connector. I found the answers I needed and posted the pinouts.

I picked up a whip antenna with legs and counterpoise. I also home brewed a SO-239 adapter so I can connect a standard antenna or dummy load. I also have a handset, morse code key, aviation headset with a mic & a high amperage 28VDC power supply.

I have gone in and switched out the mechanical filter so it now does LSB instead of USB.

I connected everything up as per the operators manual and using my SO-239 adapter I connected a Bird 43 watt meter and a Bird termaline dummy load. I set up the tuning as per the operators manual and put it into tune mode. I heard the T/R really switch and the switching transistors start their 400 Hz hum. However neither the power meter on the PRC-47 or the Bird 43 register any output. The needle doesn't even wiggle. Since it was advertised as functioning properly I contacted the guy I got it from. He came over and observed the same behavior. He was surprised it didn't transmit and said he would get it working for me. He took it home with him.

We have been in fairly regular communication and he has discovered the same problem with the other PRC-47s he owns. He has been working on the problem off and on for the last few months but has been unable to resolve the problem. I just exchanged emails with him and he says he is trowing in the towel. He plans to return it to me in a couple weeks.

I have a good original copy of the service manual which has a pretty good trouble shooting section. I plan to use this and see if I can resolve the problem myself. I expect I will have lots of questions and hope I can find answers here. I have looked for a more relavent forum, but have been unable to locate one.

I'm looking forward to this project I will let you all know when I get the radio back and set up on my bench.


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 Post subject: Re: PRC-47 Transmit issues.
PostPosted: Feb Sun 04, 2018 5:44 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5170
Good luck with it and I hope you get it operational. Mine was in good shape when I bought it but I also did the LSB modification. The transistors in the inverter are a known high failure item so checking that they are actually producing HV is a good place to start. The final tube is also known to be fairly short lived when operated in the high power position. Check to see if excitation is making it to the final.

One of the better sites covering issues is this one in case you haven't already come across it: http://k6jca.blogspot.com/2009/09/prc-4 ... tions.html

I haven't had mine on the air in a couple of years so I will plan to get it out again this Spring. Below are photos from its first testing after I went through it and installed the filter for LSB.

It is sometimes hard to believe that I will soon be teaching that little girl in the photo how to drive. The years are flying by.

Rodger WQ9E


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PRC-47 panel.JPG
PRC-47 panel.JPG [ 142.97 KiB | Viewed 207 times ]
Anna transit case.JPG
Anna transit case.JPG [ 245.97 KiB | Viewed 207 times ]
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 Post subject: Re: PRC-47 Transmit issues.
PostPosted: Feb Mon 05, 2018 12:02 am 
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Joined: Mar Thu 15, 2012 10:28 pm
Posts: 60
Roger,

Thanks for the link. It looks like there are a couple things to look at. The AGC mod transmit problem may be a clue to follow. I emailed the blog site to the seller just to see is this is any help to him.

It looks like there are a lot of good mods there too.

One other mod I have been kicking around is making USB/LSB switchable without losing CW capability. Here is my concept:

Find a way to sandwich in both the USB and LSB filters.
Add a 28VDC relay to switch out the 2 filters.
Control the 28VDC relay using a magnetic reed switch glued to the inside of the aluminum cabinet. A small plate of steel should be glued to the outside & a pull apart connector used to tie the reed switch into the circuit so the case can be removed without ripping it out of the circuit.

Then to switch from USB to LSB simply place a magnet on the small steel plate. This closes the reed switch and energises the relay.

I have experimented with this concept using a similar aluminum case, a reed switch, a small plate of steel and a magnet. It seems to work!

What are your thoughts?

Jim
KG9MM


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 Post subject: Re: PRC-47 Transmit issues.
PostPosted: Feb Mon 05, 2018 2:37 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5170
Jim,

That sounds like a workable approach as long as you can find space for both filters. Magnetic reed switches ARE great for a lot of vintage gear projects. I used one several years ago along with a relay to repair an old timer's Hallicrafters receiver that was missing the AC switch on the response switch.

Rodger WQ9E


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