Panasonic RE 784A - Printable Version
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Panasonic RE 784A - Paul Philco322 - 07-18-2019
Greetings all:
I recently was gifted this set...........
https://www.radiomuseum.org/r/panasonic_re_784re78.html
After a replacing capacitors it plays very well on FM no static when tuning, on AM on a station it plays fine when tuning on AM a lot of heavy static between stations. I am perplexed, same tuning capacitor why fine on FM and not on AM? Anyone encounter this scenario?
It is a fine sounding radio and has a nice story behind it being a gift.
Appreciate your help.
Paul
[Image: https://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Front_784.jpg/1024px-Front_784.jpg]
RE: Panasonic RE 784A - Radioroslyn - 07-19-2019
Well the long answer is this. If it was the tuning cap it's broken down into two parts one AM and the other FM.
[Image: https://upload.wikimedia.org/wikipedia/commons/thumb/6/62/Kombidrehko.jpg/698px-Kombidrehko.jpg]
The 11 plates at the front of each section are for the AM tuning and the 2 plates at the rear are for the FM tuning. So it is physically the same cap it's two different sections.
I would suspect that the problem isn't the tuning cap. Were you having this problem the last few days? Could be just noise from weather conditions? Lightening and such.
GL
RE: Panasonic RE 784A - Paul Philco322 - 07-19-2019
No I have had this issue since I got it. I did not play it till serviced so not sure if it was a long term problem. Not that sensitive on AM either though OK. Very fine on FM though. Perhaps they designed to perform on FM not so much AM.
Was wondering if it could be something in that ferrite antenna?
Paul
RE: Panasonic RE 784A - Radioroslyn - 07-19-2019
I would suspect something in the IF or mixer stages perhaps a leaky cap or bad tube. The fm detector is designed to not detect static (change in amplitude) but a shift in frequency. So in the fm mode you shouldn't hear any static. Audio stages are probably ok as you wold hear it in both am and fm if they weren't. In terms of troubleshooting I would use a large value cap (like .1mf) connected to the b- rail and the other end jumper to the control grid of the a fore mention tubes one by one. Listen to hear when the noise stops then concentrate on that area to find the defect.
RE: Panasonic RE 784A - David - 07-20-2019
Great playing radio, unable to find my notes on the one that plays in my work shop. First and only set I have worked on with a 17EW8. If I remember correctly it is used in place of a 12AT7. In reading some were about using the 17EW8 was due to increase in line voltages. I purchased several to use in place of 12AT7. At the time they were cheaper. I did replace the original tube in my set big improvement on both AM&FM. Something about a 3or4 section E Cap? Using a 1N4007, sorry about not being more helpful.
RE: Panasonic RE 784A - Paul Philco322 - 07-22-2019
Thanks for the advice, so ****hot and humid up here I have no patience for anything, will listen to FM for now and work on later.
Thank you gents.
Paul
RE: Panasonic RE 784A - David - 07-26-2019
Found my notes the 17EW8 is a sub for 12DT8. The 12DT8 has a internal shield on pin 9, the 12AT7 has a center tap to the heater on pin 9.