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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 19th May 2017, 5:24 pm   #1
stuboy57
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Default Hacker Democrat

Bought an old Hacker Democrat that was not working, the usual problem I thought, AF117's need replacing. Replaced them with AF137's, but the radio is still not working. I've cleaned the MW and LW switches plus the On/Off volume pot and still not working. When I turn on I can get feedback through the speaker from my mobile phone, which is near to the set, also if i touch the contacts on the back of the on/off volume pot I get the scratching noise through the speaker. What would be the next step to try. I'm still a bit of a newbie to vintage radios and just love these old Hacker's, any help appreciated
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Old 19th May 2017, 5:45 pm   #2
Nuvistor
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Default Re: Hacker Democrat

Check voltages in the IF and LO, test if you can hear the LO on another radio.
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Old 19th May 2017, 5:57 pm   #3
stuboy57
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Default Re: Hacker Democrat

Sorry Frank can you explain as I am still new to this forum with limited experience...but if you can talk me through the process I will try and give it a go....I have a voltmeter...thanks
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Old 19th May 2017, 6:12 pm   #4
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Default Re: Hacker Democrat

The mobile 'phone bit, is this the buzz buzz buzz thing as it keeps in contact with home? An interesting test tool.
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Old 19th May 2017, 6:13 pm   #5
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Default Re: Hacker Democrat

Have you a circuit? Available from the link at the top of this page. The circuit will have the voltages at various locations in the radio. The audio section appears to be working by the comments about the volume control and mobile phone.

I think the Democrat is MW and LW, the sections are Mixer/Local Oscillator, Intermediate Frequency amplifier, Detector and audio stages.
Check the voltages with the circuit in the Mixer/Local Osc, and Intermediate Frequency amp.

To check the local osc, tune the democrat to around 600Khz on MW and tune another radio placed next to the democrat to around 470khz higher, you should hear the LO if it is working.

See Paul Stennings web site, transistor section for lots of info on how to repair and how the radios work.
http://www.vintage-radio.com/repair-...ion/index.html

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Old 19th May 2017, 6:15 pm   #6
stuboy57
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Default Re: Hacker Democrat

Quote:
Originally Posted by merlinmaxwell View Post
The mobile 'phone bit, is this the buzz buzz buzz thing as it keeps in contact with home? An interesting test tool.
yes that it, get the same with my vintage record players get to near and you get a baa baa baa sort of sound.....move the phone away and it disappears
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Old 19th May 2017, 6:23 pm   #7
GeoffK
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Default Re: Hacker Democrat

The audio stage would appear to be working, bridge the contacts across the volume control in case this is open circuit. The next step working backwards from the volume control would be to check the detector diode. This can be tested with a multimeter either on the diode check range or the resistance range (with the radio turned off). Bridging the detector diode with a similar germanium diode such as an OA90 will show if this is where the fault is.
The IF is the Intermediate frequency stage and LO the Local Oscillator in the RF Radio frequency stage. Usually referred to as the Mixer/Oscillator as it mixes the incoming radio frequency with the Local Oscillator frequency by heterodyning to produce the fixed intermediate frequency.
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Old 19th May 2017, 6:28 pm   #8
GeoffK
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Default Re: Hacker Democrat

Quote:
Originally Posted by merlinmaxwell View Post
The mobile 'phone bit, is this the buzz buzz buzz thing as it keeps in contact with home? An interesting test tool.
Does this signal get picked up by the RF stage, in which case the RF IF and detector must be working.
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Old 19th May 2017, 6:32 pm   #9
Nuvistor
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Default Re: Hacker Democrat

Pretty sure the its the audio amp. RF break through into audio amps is common, especially near a transmitter, memories of record players and amateur radio.

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Old 19th May 2017, 6:44 pm   #10
GeoffK
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Default Re: Hacker Democrat

That's what I thought might be the case.
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Old 21st May 2017, 7:39 pm   #11
stuboy57
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Default Re: Hacker Democrat

thanks for the comments...plenty of info to try this week
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