MC-22 schematic question

[timlinca]

Hi folks,

I have a question about this schematic and I'm sure one of you could answer it. I placed a yellow arrow pointing at what appears to be some sort of shielded connection? To the left there is a center tapped potentiometer. On the wiper connection that goes to the grid of V4-A, there is a circle around the wire that actually connects to the cathode. What is that? Maybe some sort of shielded wire connecting wiper to grid and the "ground" of the cable goes to the cathode?

Thanks for your help,

Tim
p.s. I hope I actually attached the schematic photo. If not I will try to fix...

 

[DF96]

Yes, probably a cable shield. Doing it that way avoids adding extra cable capacitance at a high impedance point, yet still provides some protection from noise and hum. In effect, the cable capacitance is being bootstrapped.

 

[timlinca]

Thank you for the reply. That makes sense, it is a relatively long wire (volume control on front panel to one of the tubes) and you don't want noise entering there.

 

[Chris Hornbeck]

McIntosh did this a lot, and makes an interesting study for us DIYers. I saw their plant in 1975, and remember especially a huge room full of women. They said they didn't even try to hire men anymore - just couldn't take it!

All good fortune,
Chris