Solarus Impedance

[Ryan Phelps]

I'm restoring a 1968 Sunn Solarus.....the early combo version with EL34's, smaller transformers, etc. This amp is very clean and unmolested, just needed new filter caps and tubes. The chassis is labeled as having a 16 ohm output and indeed the O.T. color code matches the schematic....16 ohms. I checked the cabinet and the two 8 ohm, 12" Sunn-labeled speakers are wired in parallel rather than series, yielding a 4 ohm impedance. Obviously, I can rewire the speakers for 16 ohms. But the speaker wiring looks factory stock....the wire, solder joints, even the wire lacing! Have any of you guys ever seen this on a Sunn? Hard to imagine the amp could leave the factory this way! Thoughts?

Thanks!
Ryan

[pickinatit]

Only thing I can think of is  Everybody makes mistakes ??  OR,  as someone said in another thread a couple days ago,  back in the day I don't recall ever even hearing of impedance.  We used to just plug whatever speaker cabs we had into whatever amp we had and go to town.  I don't recall ever blowing anything up or burning anything out either. (Except when my parents bought me the Solarus the Music store guy did show me where to plug the speakers in on the back of the amp and warned me not to EVER plug it in "over there".  Would have been 16 ohms into the 8 ohm jack though.  Not ideal, but no harm either,  so even he didn't really know what he was talking about.)  LOL

Re-wire the speakers.  I have the piggy back version of the 40 watt Solarus.  At 16 ohms it's still louder with more headroom then you will ever need.  (You'll never overdrive the tubes without deafening yourself and everyone in a 1 block radius first either.)  I have the original 2x12 cab that came with the Solarus (except re-done with Celestion v30 and a Celestion g12h30 wired to make a 16 ohm cabinet)  and a Sunn model 2  (2x10) that's 16 ohms.  When I run the head thru both those cabs....well  it sounds pretty incredible.  The Model 2 is very bright and carries the highs and mids terrifically and the celestions handle the lows....well it just sounds great.  The reverb and "vibrato" are both first rate too IMO.

Sorry to get O.T.,  I get carried away talking about my 40 something year old friends.

Michael

[Ryan Phelps]

Michael,
Thanks for your reply! I also own a later Solarus....separate head and speaker, 6550's, larger transformers etc. Mine is near mint, 100% original. I just checked it......the head is wired for 8 ohms while the speaker cab is wired for 4 ohm (even the badge on the back says Solarus, 4 ohm)!
So, perhaps the factory wasn't paying attention to this mis-match, or didn't think it was important. Even though the output transformers had 4, 8 & 16 ohm taps; the outputs were specific and marked on the chassis; the feed back circuit was also tuned to a specific output tap; and they bothered to badge the speaker cab with a model name and impedance!
Baffling! Sunn amps were very well engineered in their day and beautifully built (I heard once that they recruited assemblers from nearby Tektronix of oscilloscope fame).
A 100% impedance mismatch is tolerable in tube amps (better if the speaker impedance is higher than the amp output). But a 200% mismatch in the 1968 Solarus would work the amp really hard and tend to eat output tubes. So re-wiring the speakers in series would match the head at 16 ohms. The down-side (other that altering the originality) is that if one speaker blows, you have an open circuit (or a dead short) without a load for the output transformer.
OK, I'm really getting into Amp-Geek-World here, so I'll sign off!

Thanks!
Ryan