speaker impedances w/solarus head

[rob g.]

I'm a little ignorant about ohms and output impedances etc.  Can I use 2 8ohm Marshall cabs with my Solarus head?  It has an 8ohm jack and a 16ohm extension jack.  Will I hurt anything by plugging them both in? or do I need to have some rewiring done?  Thanks for any help/info you can share. -Rob

[Isaac]

You might. Two 8 ohm cabinets is a total load of 4 ohms. If you turn it up much, you'd probably draw more current than the amp can safely put out. At that point, if you're lucky, you'll blow a fuse. More likely, you'll destroy your output tubes ($) or the output transformer ($$) or both ($$$).

However, there is probably an easy fix. Most Sunn tube amps had a 4/8/16 output transformer, with only two of the three wired up. Just change the 8/16 wiring to 4/8 wiring, and you should be good to go.

[rich]

I have a Solarus head with an 8 ohm jack and 4 ohm external speaker jack.  I have a 4 ohm cabinet (2x8 ohm celestions in parallel) that I'd like to use as it's easier to get down the stairs than my 8 ohm 412.  Can I just plug this into the external speaker jack with no load on the 8 ohm jack, or is it expecting both?  The schematic on this site is for an 8/16 and I'm not sure if the output stage is wired the same way.

Lots of helpful tips on here - thanks for all. This question is almost covered elsewhere (on one of the 2000s threads) but I'm being careful.

[rich]

sorry - when I say 'both' I mean an 8 ohm load on each jack.

[Isaac]

Yes, you can. When you plug into the external speaker jack, it disconnects the 8 ohm tap, and puts the output jacks in parallel on the 4 ohm jack. The jakcs are labeled for the total load of the impedance, not the individual cabinet plugged into the jack, so two 8 ohm cabinetrs get plugged into both jakcs, one into each, and one 4 ohm cabinet gets plugged into the 4 ohm jack.

Oh, and rob g., you could also run the cabinets in series for a 16 ohm load.

[rich]

Thanks for the speedy reply! That clears things up.

[AdmiralB]

FWIW I install a rotary switch and wire up all three taps, so I can select 4/8/16 for the (now parallelled) pair of jacks - Marshall style.

[JoeArthur]

FWIW I install a rotary switch and wire up all three taps, so I can select 4/8/16 for the (now parallelled) pair of jacks - Marshall style.

Sounds like a much easier way to go.  Where did you install the switch?

[Isaac]

The only objection to that would be that the amp is then no longer stock.

I don't have a problem with that, but some would, I think.

[AdmiralB]

I used the Nikkai switch that Doug Hoffman sells, and just drilled a hole next to the speaker jacks (or, on my 2000S, in the RCA block-off plate).

Yes, the amp is no longer stock, but we are talking about $350-$500 amps here.  The 200S is not, and IMO never will be a plexi Super Lead.

[JoeArthur]

The only objection to that would be that the amp is then no longer stock.

I don't have a problem with that, but some would, I think.

Hmm... let's see... wasn't there a Ricky Nelson song...

"Ya can't please everyone, so ya got ta please yerself".

[Isaac]

Are we still talking $300-$500 amps after they've been modified?

Again, not a problem for me. I don't intend to sell mine for a long time. Probably at my estate sale!

[AdmiralB]

I dunno, but if you're buying Sunn amps as an investment...OK, don't drill any holes.  But don't get ready for that early retirement, either.

I think most people who buy these are either going to play them, in which case an impedance selector makes a lot of sense...or they're just collecting them because they're a steal in terms of a 'vintage' hand-wired amp...in which case it probably doesn't matter.

I replace the two-conductor mains cables and remove the polarity cap too - and I haven't seen any effect on prices yet.  Which you can't say about Fender.