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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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4th Feb 2019, 11:27 pm | #21 |
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Re: Civic R4900. No sound from main speaker.
That is a small capacitor which is confirmed by C69 on the board. It may be there to bypass high frequencies on the big speaker and will kill the sound completely if it is short circuit
Have you found a schematic? There does not seem to one on the V-R CD. |
4th Feb 2019, 11:31 pm | #22 |
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Re: Civic R4900. No sound from main speaker.
That doesn't appear to be a doide and what made you think that this component is at fault?
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4th Feb 2019, 11:32 pm | #23 |
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Re: Civic R4900. No sound from main speaker.
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4th Feb 2019, 11:33 pm | #24 |
Triode
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Re: Civic R4900. No sound from main speaker.
This is what I could find online
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4th Feb 2019, 11:38 pm | #25 |
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Re: Civic R4900. No sound from main speaker.
The circuit for the R4900 is available on https://elektrotanya.com/ as the VIDEOTON MELODYN R4900
Here is an extract. |
4th Feb 2019, 11:40 pm | #26 |
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Re: Civic R4900. No sound from main speaker.
Circuit available here:-
https://www.radios-tv.co.uk/communit...c-r4900-radio/ That looks like a perfectly good capacitor to me having removed it the chances are the tweeter no longer works.
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4th Feb 2019, 11:41 pm | #27 |
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Re: Civic R4900. No sound from main speaker.
C69 is a 150pf capacitor connected from the anode of the Triode section of the ECL86 to chassis.
It is not the fault, these ceramic capacitors are hollow, it may case instability now it is not in circuit but not the fault of the tweeter working but not the main speaker.
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4th Feb 2019, 11:43 pm | #28 | |
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Re: Civic R4900. No sound from main speaker.
Quote:
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4th Feb 2019, 11:49 pm | #29 | |
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Re: Civic R4900. No sound from main speaker.
Quote:
I still think the fault is in the extension speaker socket. Whatever the fault is a bit of continuity testing would soon find it.
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4th Feb 2019, 11:50 pm | #30 |
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Re: Civic R4900. No sound from main speaker.
Re: Post#20: So far as I can make out that might be the chassis connection (for the loudspeaker) one end of C69 is connected to chassis and the other end of C69 is connected to the anode of the triode section of the ECL86, the schematic I have is not too clear but that's my best guess at the moment:
https://nvhrbiblio.nl/schema/Videoton_R4901.pdf EDIT: Post crossed...twice....nay 9 replies Lawrence. Last edited by ms660; 5th Feb 2019 at 12:10 am. Reason: Ref to post 20 added |
4th Feb 2019, 11:55 pm | #31 |
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Re: Civic R4900. No sound from main speaker.
It might be better if you tried to identify and become familiar with certain components and what they are. That 150pF ceramic capacitor was likely perfectly OK and is an IF bypass used to filter out any IF signal that may find its way to the output valve and cause instability. Looking at that output stage, the speaker wiring couldn't be much simpler and not much will stop the main speaker from working. Assuming the speaker is OK all that is left is the speaker wiring and the ext speaker switch (shown in the circle above the speaker and marked 1,2,3,4. The switch connection is between 3 and 4 and would be the first thing I would check.
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4th Feb 2019, 11:57 pm | #32 |
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Re: Civic R4900. No sound from main speaker.
Hi Graham,
The speaker has a chassis connection and so does the C69 so it’s possible the speaker wire chassis connection is at the same point as C69. Like you I think some simple continuity testing should find the problem.
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5th Feb 2019, 12:18 pm | #33 |
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Re: Civic R4900. No sound from main speaker.
C49 is a ceramic tube with one plate inside the tube and the other on the outside. It looks good to me.
C49 may be saved if you wind a small helix with thin wire and slip it over the dog ends of the capacitor lead and solder it. Connect another speaker directly to the output transformer so that the external plug is not involved. |