Why do some radio manufactors put in a electrolytic cap across the Cathode resistor and some do not. I know it has to due with bypassing certain low audio frequencies. The size cap is around 10mfd @ 25-50 VDC. On another thought, what would change or for the better or worse if you installed a bypass cap across the 12SK7 IF amp Cathode resistor.

:Why do some radio manufactors put in a electrolytic cap across the Cathode resistor and some do not. I know it has to due with bypassing certain low audio frequencies. The size cap is around 10mfd @ 25-50 VDC. On another thought, what would change or for the better or worse if you installed a bypass cap across the 12SK7 IF amp Cathode resistor.
:
Hi Frank,
I have not often seen cathode capacitors across the power output tubes in AC/DC sets. This is rarely done, or never done, because suppression of 60Hz hum is a main consideration in these sets and a bypass capacitor helps pass 60Hz. Leaving it off helps suppress 60Hz hum.
As for a bypass capacitor on a 12SK7, I have seen 0.005uF or there a bouts in that place. One wants to make sure the IF is passed. I usually see that in the circuit.

Best Regards,

Bill

::Why do some radio manufactors put in a electrolytic cap across the Cathode resistor and some do not. I know it has to due with bypassing certain low audio frequencies. The size cap is around 10mfd @ 25-50 VDC. On another thought, what would change or for the better or worse if you installed a bypass cap across the 12SK7 IF amp Cathode resistor.
::
:Hi Frank,
: I have not often seen cathode capacitors across the power output tubes in AC/DC sets. This is rarely done, or never done, because suppression of 60Hz hum is a main consideration in these sets and a bypass capacitor helps pass 60Hz. Leaving it off helps suppress 60Hz hum.
: As for a bypass capacitor on a 12SK7, I have seen 0.005uF or there a bouts in that place. One wants to make sure the IF is passed. I usually see that in the circuit.
:
:Best Regards,
:
:Bill
:

:::Why do some radio manufactors put in a electrolytic cap across the Cathode resistor and some do not. I know it has to due with bypassing certain low audio frequencies. The size cap is around 10mfd @ 25-50 VDC. On another thought, what would change or for the better or worse if you installed a bypass cap across the 12SK7 IF amp Cathode resistor.
:::
::Hi Frank,
:: I have not often seen cathode capacitors across the power output tubes in AC/DC sets. This is rarely done, or never done, because suppression of 60Hz hum is a main consideration in these sets and a bypass capacitor helps pass 60Hz. Leaving it off helps suppress 60Hz hum.
:: As for a bypass capacitor on a 12SK7, I have seen 0.005uF or there a bouts in that place. One wants to make sure the IF is passed. I usually see that in the circuit.
::
::Best Regards,
::
::Bill
::
:
:

:::Why do some radio manufactors put in a electrolytic cap across the Cathode resistor and some do not. I know it has to due with bypassing certain low audio frequencies. The size cap is around 10mfd @ 25-50 VDC. On another thought, what would change or for the better or worse if you installed a bypass cap across the 12SK7 IF amp Cathode resistor.
:::
::Hi Frank,
:: I have not often seen cathode capacitors across the power output tubes in AC/DC sets. This is rarely done, or never done, because suppression of 60Hz hum is a main consideration in these sets and a bypass capacitor helps pass 60Hz. Leaving it off helps suppress 60Hz hum.
:: As for a bypass capacitor on a 12SK7, I have seen 0.005uF or there a bouts in that place. One wants to make sure the IF is passed. I usually see that in the circuit.
::
::Best Regards,
::
::Bill
::Thanks for the info. I came across one radio that had a bypass cap installed from the factory and someone clipped it out (one side disconnected). A few radios had multisection electrolytic cap with a bypass cap 25mfd section.
:
:

The capacitor in the cathode circuit is to keep the DC voltage constant. Without this cap the voltage can vary and reduce the gain of the amplifier. Reduction is accompanied by a reduction of distortion so in hi-fi circuits the cap is often omitted. If the cathode bypass capacitor is left out of the circuit,several things about the amplifier will change. The two most important are a reduction of gain and a reduction of distortion. The former is not good by itself but the latter is so good that it is worth the lost gain.

:The capacitor in the cathode circuit is to keep the DC voltage constant. Without this cap the voltage can vary and reduce the gain of the amplifier. Reduction is accompanied by a reduction of distortion so in hi-fi circuits the cap is often omitted. If the cathode bypass capacitor is left out of the circuit,several things about the amplifier will change. The two most important are a reduction of gain and a reduction of distortion. The former is not good by itself but the latter is so good that it is worth the lost gain.

The above is exactly correct. If you want, you can play around with different values of capacitors, as the reactance of the cap will very much change the frequency response, too. Find one that sounds good to you and leave it there. Or, if you are a purist about keeping things original, install the factory value and learn to like the way it sounds.
Lewis
:

:The capacitor in the cathode circuit is to keep the DC voltage constant. Without this cap the voltage can vary and reduce the gain of the amplifier. Reduction is accompanied by a reduction of distortion so in hi-fi circuits the cap is often omitted. If the cathode bypass capacitor is left out of the circuit,several things about the amplifier will change. The two most important are a reduction of gain and a reduction of distortion. The former is not good by itself but the latter is so good that it is worth the lost gain.
:
I agree with Warren's description. It is consistant with the one I offerred but is more detailed and goes further.

All the Best,

Bill

:Why do some radio manufactors put in a electrolytic cap across the Cathode resistor and some do not. I know it has to due with bypassing certain low audio frequencies. The size cap is around 10mfd @ 25-50 VDC. On another thought, what would change or for the better or worse if you installed a bypass cap across the 12SK7 IF amp Cathode resistor.
:
As to the 50L6 'why' question, it was frequently $$$ by the manufacturer. Radio works ok without, and the speaker / circuit wasn't exactly hi-fi. As to the 12SK7, cathode resistor wasn't always used. When / where a cathode resistor is used, bypassing the cathode resistor with a cap will increase the gain, but may cause oscillation. EdM