Hi everybody,I have here a terrific Fada radio model KO 51 superetherodyne in TLC condictions.Since,probably,tone control was defect,they eliminate the tone control switch,that is,according to the Fada schematic, an usual 3 clicks position switch with resistor and capacitor in series coming from the end of choke coil.Now,I want to put back a new tone control, but using a 25000 ohm wire control having one side with a capacitor of may be 56000 PF coming from the plate of #47 tube and the central tap grounded.Is it a good solution? The capacitor value of 56000 PF is enough or too low according with a just 25000 OHM wire control? Let me know folks and thanks.

regards from ITALY Umberto

In order to be able to turn off the tone control, your variable resistor must have a DC resistance far higher than the AC impedance of the output transformer and tube, which is usually several thousand ohms. Your variable resistor control (potentiometer wired as rheostat) should be at least 500K. The condenser wired to it should be anywhere from .005 MFD to .05 MFD, and should be chosen according to what yields the best tonal characteristics while operating the control over its entire range. There is no set formula for this, as a condenser does not simply pass a certain band of frequencies, but passes all frequencies, declining as the frequencies get lower. The above value condensers are those that yield a variety of favorable results in most radio receivers. You must pick a value that you like.

I like your original tone control set-up, though. It is a nice one that has a low, music, and speech setting. Why not just obtain a new three position switch and put back the original tone control? This, too, can be tailored to your taste. This is your schematic: http://www.nostalgiaair.org/PagesByModel/494/M0043494.pdf

Thomas

Well, come to think about it....you'd probably be better off with the variable resistor set-up. The original three position set-up is no different really, but the variable resistor will give you more options.

Thomas