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 Post subject: Broadcast band
PostPosted: Apr Sat 06, 2019 7:55 pm 
Member

Joined: Jul Sat 09, 2011 7:49 pm
Posts: 44
Location: Santa Cruz,ca
Hello, I have a couple radios in my collection where the broadcast band does not tune below 800kHz give or take! What are the possible causes of this? Thanks for your help.
Jerry


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 Post subject: Re: Broadcast band
PostPosted: Apr Sat 06, 2019 9:28 pm 
Member

Joined: Jul Wed 22, 2009 3:07 pm
Posts: 772
Hi Jerry,

Chances are someone played with the settings on the radio.
Best approach to correct this is to do a full alignment based on the service manual.
If you can not find a service manual, that is not a problem either, transistorized MW radios follow well known patterns.
In short, first you align the IF-amplifiers, then you set the band limits by adjusting the oscillator stage, and finally tune up the antenna circuit.
Let us know if you any help with the details.

Regards, Peter


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 Post subject: Re: Broadcast band
PostPosted: Apr Thu 18, 2019 9:55 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11565
Location: Powell River BC Canada
From way back when service, the oscillator might be stopping
because the germanium transistors have gotten leaky.

A simple way to test this is with a radio that has a BFO.

Track the radiated signal at 1450 kHz (with the transistor radio tuned to
1000 kHz.)

Then back it down to where the hetrodyne peters out.

Old Sony 2T73 transistors did this sometimes.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Broadcast band
PostPosted: Apr Sat 20, 2019 7:38 pm 
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Joined: Mar Sun 20, 2011 2:53 pm
Posts: 773
Location: Spain - 28110 - Algete
Try to test the variable capacitors for shot circuit on lowest part of band.


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