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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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26th Mar 2007, 4:20 am | #1 |
Heptode
Join Date: Jan 2007
Location: Parkes, NSW Australia
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Testing local oscillator.
What's the best way to see if the local oscillator in a set is working?
TIA Peter Last edited by Darren-UK; 1st Oct 2007 at 1:00 am. Reason: Typo corrected to aid search. |
26th Mar 2007, 6:52 am | #2 |
Hexode
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Re: testing local oscillator
Peter,
A quick test is to hold a (transistor, usually) portable set up close, tuned to the middle of the medium waveband, and tune the radio under test across the MW band. If the local oscillator is working, there'll be all sorts of heterodynes [whistles] audible on the portable set as you do this. HTH! Dave
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Dave Teague |
26th Mar 2007, 3:15 pm | #3 |
Octode
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Re: testing local oscillator
For valve sets with the typical triode / hexode type frequency changer, if the oscillator is running, the triode grid will show a negative voltage when measured with a DC meter.
Dave's suggestion is less intrusive though as there is no need to poke around under the chassis. John |
27th Mar 2007, 8:08 pm | #4 |
Rest in Peace
Join Date: Jun 2006
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Re: testing local oscillator
The replies given to the Q. so far are fine when the Q,. is regarded in its broadest sense.
However, to me, "the best way to see if the L.O. is 'working' " implies a basic check on its frequency, purity of waveform, variation in level & freq. when tuning is changed, etc. For this, a 'scope with a high-impedance probe is required. Or possibly a spectrum analyser. Al / Skywave. |
28th Mar 2007, 5:13 am | #5 |
Heptode
Join Date: Jan 2007
Location: Parkes, NSW Australia
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Re: testing local oscillator
Should one attach the scope probe to the oscillator grid?
Peter |
28th Mar 2007, 8:22 am | #6 |
Dekatron
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Re: testing local oscillator
The anode is better, Peter - lower impedance.
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Mike. |
28th Mar 2007, 2:34 pm | #7 |
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Re: testing local oscillator
Just one small thought on this.
What Mike Phelan has said will be appropriate for the vast majority of cases. But since we are not discussing any particular set here - therefore I'm reading this in a very general context - be aware that there are some (albeit rare) oscillator circuits that have a r.f. grounded anode. So, if you do find no signal at the anode, and the cct. diag. is available, have a close look at it. And good luck! Al / Skywave |
9th Apr 2007, 7:51 am | #8 |
Heptode
Join Date: Jan 2007
Location: Parkes, NSW Australia
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Re: testing local oscillator
Many thanks for all the answers, guys.
Peter |