On many of the older tube type base radios, there is a capacitor (like a
4uf) on each the pins of the mic connector...like on a 4 pin mic male
connector there might be 4 each caps, wired in series, with a leg of the
cap wired to one of the pins with one leg of the caps going to ground.

Question is:
1-why is this done
2-what is this suppose to do
3- if the caps are not used what will be the outcome

Thanx!!

On many of the older tube type base radios, there is a capacitor (like a
4uf) on each the pins of the mic connector...like on a 4 pin mic male
connector there might be 4 each caps, wired in series, with a leg of the
cap wired to one of the pins with one leg of the caps going to ground.

Question is:
1-why is this done
2-what is this suppose to do
3- if the caps are not used what will be the outcome

Thanx!!


They are RF bypass caps. They shunt stray RF picked up
by the mic cord to GND before it gets into the 1st audio stage.
See any ARRL handbook for more info.

They are used to stop RF from going to the mic which could cause it to
squeal. Also used to stop TVI by stopping the mic cord from becoming
an TX antenna.

Homer

Hi Sir Tube Man!
I like details on tube stuff! What kind of radio? I have and use
regularly a Johnson Viking Messenger. Yes, those caps stop RF, but 4uF
sounds too big! That would muddy the audio on the audio pin.. .01uF
caps should work fine as long as they're short leaded.
Hydro

On Fri, 10 Jun 2005 04:04:32 GMT, "The Tube Man"
wrote:


On many of the older tube type base radios, there is a capacitor (like a
4uf) on each the pins of the mic connector...like on a 4 pin mic male
connector there might be 4 each caps, wired in series, with a leg of the
cap wired to one of the pins with one leg of the caps going to ground.

Question is:
1-why is this done

To prevent 60/120 cycle noise from entering the radio on receive.
Older tube radios routes the cathode of a one or more tubes through
the mic connector to control transmit.

2-what is this suppose to do

see above

3- if the caps are not used what will be the outcome


chances are that there maybe some ac hum in the receive or transmit.

james

On 10 Jun 2005 09:34:49 -0700, "HarryHydro"
wrote:

Hi Sir Tube Man!
I like details on tube stuff! What kind of radio? I have and use
regularly a Johnson Viking Messenger. Yes, those caps stop RF, but 4uF
sounds too big! That would muddy the audio on the audio pin.. .01uF
caps should work fine as long as they're short leaded.
Hydro
*****

More likely to help in AC (60/120 cycle) ground loops causing hum in
receive or transmit low level audio sections.

You are right to keep RF out one would use say 0.01 micrfarad caps.
Even 100 pF caps for stubborn higher frequency harmonics.

james