Panasonic RF 5000 hiss

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Hepsibar
New Member
12
Jan Wed 11, 2023 11:03 am
Perth. Western Australia 6101

Panasonic RF 5000 hiss

Post by Hepsibar »

My ebay radio has a constant hiss, (seller was great and told me about this) unaffected by the volume control. I am presuming a bad transistor on the amp board and I have some spare transistors. All bands seem to work as presding the band buttons alows am signals, fm, and short wave to be recieved if I crank the volume to drown out the hiss!

Could this also be caused by old capacitors?
Any help with this beautifull radio apreciated.
rcadanny
Member
1244
Dec Mon 23, 2019 4:52 pm
Sandy Springs, Georgia 30328

Re: Panasonic RF 5000 hiss

Post by rcadanny »

I've never had a capacitor cause hiss, but plenty of transistors have. Usually, it's one between the volume control and the output driver circuit. I've never run into an output transistor causing hiss. Freeze spray, or a soldering iron tip held close to the suspected transistor will help narrow the problem down.
Hepsibar
New Member
12
Jan Wed 11, 2023 11:03 am
Perth. Western Australia 6101

Re: Panasonic RF 5000 hiss

Post by Hepsibar »

Ok thanks that transistor will be the first to test! Oh and of course its probably one of the harder ones to get to. Looks like TSB345. 1st IF amp on schematic. I have one ordered so will wait for its arrival.

Many thanks ahain
johnt46
Member
69
Aug Thu 23, 2018 12:11 pm
Ashburn, VA

Re: Panasonic RF 5000 hiss

Post by johnt46 »

As mentioned in an earlier response, since the noise level is not affected by the setting of the volume control the noise source is "downstream" of the volume control. You should be able to further localize the source by adjusting the Treble control; if the noise level increases as the Treble control is advanced the source is most likely associated with the first audio amplifier transistor (TR12, a 2SB345). If changing the Treble control does NOT change the noise level, I'd place my bet on the second audio amplifier stage (TR13, also 2SB345).

Carbon film resistors that carry DC current often become noisy with the passage of time, so I'd also suspect the un-bypassed portion of the emitter resistances in the two amplifier stages, R70 in the case of the first audio amplifier, or R82 in the second amplifier stage.

The two large speakers give the RF-5000 exceptionally good audio, but then again the radio IS almost as large as a 1960's console! Good luck with it.
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