This radio has been re capped BUT the problem still is there. The volume goes down , the light bulb (47) dims and then comes back in a moment or two. What should I look for? This radio has a movable bulb that turns with the dial. It illuminates as it turns to stations.

IF the suspicion is JUST related to this problem being associative to the dial lamp proper......


After consulting the sets schema…and if it is as you say, with the pilot lamp actually transversing across the dial scale.

It certainly seems plausible that within the wiring feeding to the dial lamp that……after eight thousand, four hunna' and ‘lebenteen moves, that the wire has broken internally inside its covering insulation on that bottom wire that is shown on the schema.

The top wire would shut off raw AC to the plate so in that case the radio would be silent.

Another consideration would be a time oxidized contact between the lamp and its socket.

The last scenario being an intermittent filament within the pilot lamp.

All of these possible conditions would be coincident with a light level shift, along with a developed B+ shift from the rectifier circuitry.

73's de Edd

Hi, Del: It seems that somethimg intermittent is dragging the B+ down, probably a partial short somewhere. Since the pilot lamp is dimming too, it seems that B+ will be going down throught the set. (You can verify this by watching the plate voltage at each of the stages.)

Two approaches here. First, try to wiggle all the B+ connections (with a wooden stick?), and see if you can cause the volume to drop.

The next idea would be to sytematically disconnect the various branches of the B+ supply, one by one, until you find the one the stops the lamp from dimming intermittently.

This could be a tube, I suppose, but it seems unlikely. This is pretty much a standard AA5, so maybe you have another set of tubes to try? Here's the schematic: http://www.nostalgiaair.org/PagesByModel/677/M0007677.pdf
Doug

:This radio has been re capped BUT the problem still is there. The volume goes down , the light bulb (47) dims and then comes back in a moment or two. What should I look for? This radio has a movable bulb that turns with the dial. It illuminates as it turns to stations.

I like Edd's theory, too.
Doug

I put in a new 47 and that helped a lot. It helps when the radio tuner is spot on with the station. Also put in a new .05 600 from plug in as shown on the schematic. Seems to be a lot better. Thanks

If the pilot lamp goes dim and the volume goes down, and then it comes back up and the bulb gets bright again, this is a classic example of a broken tube heater that makes a connection until it gets warm, and then bends, breaks the connection, cools, and then reconnects. Do the tubes dim down when this problem occurs? If so, that's your problem....or perhaps a broken wire??

T.

:If the pilot lamp goes dim and the volume goes down, and then it comes back up and the bulb gets bright again, this is a classic example of a broken tube heater that makes a connection until it gets warm, and then bends, breaks the connection, cools, and then reconnects. Do the tubes dim down when this problem occurs? If so, that's your problem....or perhaps a broken wire??
:
:T.

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Wouldn't shorting in the B+ cause the bulb to get brighter rather than dimmer, due to some of the currrent flowing through the rectifier tube?
Lewis