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Valve radio repairers?

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    #32
    fraglerocks
    Registered Users Posts: 11 ✭fraglerocks


    Watty,

    Thanks for the last advice. Attached are photos of the Murphy A168 chassis. As you can see wiring is a bit messy so its a bit hard to know what's what on the circuit diagram. Labelling is practically non-existent so I don't know what's what... Two of the capacitors (circled in red) seem to have leaked in the past. No info on them as to what they are rated. Also, two bulbs seem to be gone. I think they're 2V. The valve also circled has lost alot of its coating. Should it be replaced?

    Have you any idea where C41 is on the chassis photos? What is its significance and why is it important for it to be changed? :confused:


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    #33
    watty
    Registered Users Posts: 32,417 ✭✭✭✭watty


    If C41 is leaky then the output transformer, output tube, HT dropper resistors are all having too much current. One or more fails! :(

    The Audio Transformer and 6P25 output valve are more expensive to replace than buying a whole similar radio!

    Start at Loudspeaker. It's driven by output transformer which connects between o/p valve (tube) anode pin and HT (200V to 275V DC ).

    pin numbers are clockwise from underside.

    The C41 connects to o/p valve grid pin.

    It doesn't matter for now about the screening paint. You can use spray on nickel or tie on aluminium foil if it's a problem. Likely not

    The large 6P25 is audio out
    from underneath
    Pin 1 to left of notch and pin 8 to right

    Pin 5 is grid from R22 47K = Yellow Purple Orange, connected to C41 and R23 Yellow Purple Yellow.

    Pin 3 is anode to audio out transformer

    The C41 other end connect to 6LD20 Anode which is pin 2 (2nd pin clockwise underneath) and the anode has 100K = Brown Black Yellow connected.

    so the pale yellow Dubilier vertical in the photo just to right of pair of cans is likely C41
    211511.jpg

    Bottom Can is likely C29 4uF, upper C43 16uF. If there is a yellow purple orange resistor (47K) between them.

    The bulbs are usually 6.3, 6.5 or 7V 100mA or 300mA. Never 2V anyway. 6.0V torch bulbs will last only days.

    Trace out from 6P25 pins marking component designation on the photo.

    Component codes
    http://www.radiomuseum.org/forum/for_beginners_prefixes_and_codes.html

    Note that "unused" valve (tube) base connections are often used as "connection tags" to hang parts that might not even connect to the tube at all!


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