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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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19th Feb 2007, 10:52 pm | #1 |
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Philips B3X10A - DM71 Magic Eye operation.
I'm repairing an old Philips model B3X10A, and I've noticed that the magic eye indicator type DM71 is alyaws showing "maximum signal", even if the set is completely out of tune. Before changing a open-circuited 820KOhm resistor, which feeds the magic eye (I think), that valve was always off. Could you help me find the problem?
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20th Feb 2007, 9:55 am | #2 |
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Re: Philips B3X10A - Magic Eye always on
Maybe faulty AGC decoupler or high-value resistor in AGC line?
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Mike. |
20th Feb 2007, 10:56 am | #3 |
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Re: Philips B3X10A - Magic Eye always on
I don''t actually own anything with a working DM71, but I believe these show maximum deflection with no signal, and the indicator shrinks as the signal is tuned in.
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20th Feb 2007, 12:58 pm | #4 |
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Re: Philips B3X10A - Magic Eye always on
If I recall correctly, the amount of shrinkage can be quite small!
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20th Feb 2007, 1:12 pm | #5 |
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Re: Philips B3X10A - Magic Eye always on
Yes, they are small, some would say not very good!, but used they were. I haven't got the circuit for your radio, but below is a DM70 (Similar) as used in a Tape Recorder - for what it's worth, this machine is the Elpico-Geloso model They were a 4 pin thing which looked like an Exclamation Mark.
The HT goes to the Anode, the signal to be 'measured' goes to the grid, via 0.22M Resistor, then the Diode shown. In your radio, I would check here. Cheers, Steve P
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21st Feb 2007, 9:42 pm | #6 |
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Re: Philips B3X10A - Magic Eye always on
Yes, it was a high-value resistor in the AGC line. It's a 1.5MOhm resistor, measuring 8.43MOhm. Thanks a lot!
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