[dconant]

Hello, 

Now that my 38-10 is playing well I really don't like the tone. It has two positions and uses .03 and .008 caps. I don't like either position as one is too low and the other is too high. So if I were to lower the high or lower the lows which way would I go on the caps?

Thanks,
Dan

   

[morzh]

Experiment.

To lower highs you have to increase overal capacitance. For this you need to increase the 8nF cap (it acts when it is not shunted and will shunt highs more if it is increased).
If you want lower the low, you need to increase the 30nF cap (when 8nF is shorted it shunts the highs more than the lows, but it will shunt the lows more when increased, together with highs of course). This said, this is a bad way to regulate bass.

[MrFixr55]

Try this.

You always need a cap across the pentode to snub parasitic oscillations. Try a 0.005 uF cap across the output.

You can then add the usual tone control circuit in the 1st audio stage by replacing the tone switch with a tone potentiometer with the center pin to chassis ground and a 0.005 uf cap between the plate of the 1st audio stage and the full CW pin of the pot. This will allow you continuous treble attenuation.

[dconant]

MrFixr55 just so I understand where is the snubber cap on the 42 tube with the switch shown as it is. Also when you say across at what points is across?

Dan

[RodB]

It would be plate to cathode or plate to ground or more common across the opt primary.

[morzh]

SInce there is alwasy a capacitor connected from the plate to K, the tone ctl serves as a anubber too.

[MrFixr55]

Hi Dan,

Yes, replace the entire present tone circuit with a 0.005uF cap from the plate of the 6F6 to its cathode (at chassis ground potential.

The variable portion of the tone control moves from its present location to a 0.005 uF cap and a tone control potentiometer (I think about a 500K audio taper pot will do).  The connection is simple.  One end of this 0.005uF cap connects to the triode plate of the 1st audio amp or to the grid of the output tube.  The other end goes to the leg of the pot that the wiper touches when full CCW. (This is a correction from my previous post.)  The wiper terminal goes to chassis ground.  As a comparison, here is the Audio section of a similar set, the Philco 41-240:
   

The control can be mounted in the hole previously occupied by the tone switch.  This will allow for continuous variation instead of the switch which provides almost no treble attenuation vs too much attenuation.

Hope this helps.