20-09-2016, 06:39 PM
(This post was last modified: 20-09-2016, 06:49 PM by radioman.
Edit Reason: added further sentence
)
Hi Ken,
As has already been noted, there are issues with the circuit diagram - the valve symbol isn't present and the +15V and -15V legends near C3/C6 are wrong as well, so if I get time I'll have a go at redrawing/modifying it so that it's easier to see what's going on.
I'm pretty sure the valve is just acting as a cathode follower as has already been said.
When you remove one valve there will be a large negative-going pulse across the 4.7k cathode resistor (which is connected to -15V) and this is pulling current through the op-amp coupling capacitor CD11/12. These are shown as electrolytics, and the bigger they are the longer they will take to charge.
This will cause the op-amp output to swing to one of the supply rails for a time, hence the muting of one channel.
Not sure how the signal returns though or whether this is the best way to understand the circuit !
Does the signal disappear again after a minute or two ?
Andy
As has already been noted, there are issues with the circuit diagram - the valve symbol isn't present and the +15V and -15V legends near C3/C6 are wrong as well, so if I get time I'll have a go at redrawing/modifying it so that it's easier to see what's going on.
I'm pretty sure the valve is just acting as a cathode follower as has already been said.
When you remove one valve there will be a large negative-going pulse across the 4.7k cathode resistor (which is connected to -15V) and this is pulling current through the op-amp coupling capacitor CD11/12. These are shown as electrolytics, and the bigger they are the longer they will take to charge.
This will cause the op-amp output to swing to one of the supply rails for a time, hence the muting of one channel.
Not sure how the signal returns though or whether this is the best way to understand the circuit !
Does the signal disappear again after a minute or two ?
Andy
