Ekco c501 tone control puzzle

[B.Taylor]

Hello,
Does anyone know why the tone control does not work when using the gram sockets on this radio. The chassis is I believe the same as the pb289 (see photo) I cannot find a schematic for this model but I read it is almost electrically identical to the pb189, the main difference being the magic eye.

Bill

[cathoderay57]

Hi Bill, I couldn't find a circuit for either the c501 or PB289 either. There is one for the C511 and PB189 from the link top right of this page (Service Data). The tone control arrangements are different in each circuit, the C511 being more sophisticated being driven from a separate feedback winding on the output transformer, whereas the PB189 is a straightforward top-cut rheostat and capacitor filter across the anode of the output valve. In neither case is the functionality any different on radio or gram. If yours is similar to the C511 the possibilities exist of either leaky filter capacitors in the tone control network (same applies to PB189) or an open circuit feedback winding although the tone control would still work albeit less impactful, and in either case the fault would be apparent on radio as well as gram. Can you be more specific, particularly as to what device you are playing through the gram sockets? Jerry

[B.Taylor]

Hi Jerry,
thanks for reply.
The tone control is very effective on radio.
Through the gram sockets I have tried an add on HMV deck from around 1937 and also a bluetooth receiver. With both of these the tone control has no effect at all.
As you say looking at the circuit diagram for similar models there is no reason for this.
I guess I will have to remove the chassis to see what is going on.
Bill

[stevehertz]

Either a wiring error or anomaly, or maybe the thinking was that for some reason tone correction wasn't needed or desirable when using the gram input.