Impedances

[Tom]

Hi all - first time poster.

Recently got my hands on the amp I wanted in 1969 and couldn't afford - a Sunn 2000S.  I've been running a Peavey 2X15 with Black Widow guitar speakers and a Peavey 1X18 front-radiating sub. One picks up where the other leaves off, and the reproduction is more-or-less flat from top to bottom. I was using a Peavey Super Festival F-800B that was designed to run at 2 ohms, so pushing the two 4 ohm cabs was perfect for it. Now, I notice that the 2000S has two speaker outs - one marked 8 ohm and one marked 16 ohm extension speaker. My dilemma is this: I don't know whether to re-wire the 2X15 in series to make it a 16 ohm cab, which means I can't use my 1X18 ever again, or to rig a serial speaker harness to make the two cabs a single 8 ohm load? In either case, if I lose a speaker live, I'm screwed. Conversely, if I re-wire my 2X15 for 16 ohms, and the 2000S gets dropped or quits while I'm performing, my Peavey F800B will be useless as a backup amp.
I've played this transistor head since 1975, and am unsure what the output wiring scheme of the 2000S is, why the two jacks have different impedance levels marked, or even what the safe operating limits of impedance are (and how they affect tube life and sound) on this large tube amp.

In other words:
HAAALP!!!

Thank you.
Tommy

[Lloyd]

Tommy,
The best I can tell from looking at a schematic of the Sunn 1200S in Aspen Pittman's "THE TUBE AMP BOOK", the output of Sunn's 120W amp design,uses the 16 ohm tap for the main speaker, and via "switching jacks", picks off the 8 ohm tap when adding another 16 ohm extension cabinet. The two cabs in parallel equalling 8 ohms. I am assuming that the 2000S Cabinets are 16 ohm systems, having the two 8 ohm speakers wired in series. My suggestion would be to leave the 2X15 at 4 ohms, wire the special harness to allow using both cabs in series, then plug into the extension speaker jack, which should connect to the 8 ohm tap. Then carry the Peavey head as a backup. If you lose a speaker in either cab, just switch over to the good cab and connect it to the Peavey head. Having the backup amp is not a bad idea....in case the Sunn gives out before any of the speakers. Hope this has been of some help. Good luck!
Lloyd