135W Ultralinear Twin Reverb: Questions about wiring in Ext Cab and NFB section

[darrellcheng]

Hello I want to run a cab along with my internal speakers, and I'm having a bit of trouble figuring out what the correct impedances should be.
Right now I have a 4 ohm load into the internal Speaker Jack, and I think the impedance for the external cab should be a 4 ohm load, is that correct?
How is that whole thing wired? I'm having trouble reading the external speaker jack, the large black bar and the other 2 rectangles side by side.

Looking at the upper right of the schem is the NFB and OT secondaries.

What is the .01 cap paralleled with the 820 ohm resistor?

Thanks!

[Enzo]

REfer to the other discussion of the Fender input jack.

That vertical black bar is a lifter - it represents a plastic spacer that is moved by the tip contact. it in turn operates a separate set of contacts - those rectangles to its left. Those contacts do not touch the plug, they are merely actuated by it mechanically.

When you plug into that external jack, the tip contact is pushed upwards by the plug. This shoves that lifter, which in turn pushes apart the two contacts.

[Krwkka]

You are correct. When you plug in the second set of speakers, the jack kicks in the 8 ohm transformer tap and puts the two cabs in series. Thus, two 4 ohm cabs would give you the correct load.