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[staceyz]

Hi, I have an old Sunn Sonaro amp (missing all the tubes) I opened it up, and it has a date stamp on the side of the chassis as 1971. I've read there are a couple configurations of tubes needed, depending if it is a 40 /60 or 80 watt amp. How do I find this out. I've attached photos of the amp. Thanks! Stacey

[EdBass]

That '71 should be a 60/80 watt amp, the '71s I've had were 60 watters with tube rectifiers but I don't see the hole for the rectifier tube socket on yours.

12AX7
6AN8
6550 or KT88 X 2

There are a bunch of things I don't see in your pics. You need much more than just tubes in that amp, it's pretty hacked up. Looks like that old girl may have been pillaged for parts. That power transformer is gigantic, and while generally bigger is better in the world of transformer, it ain't right for your amp.

I suspect you could buy another functioning 60 watt Sunn for about the same or maybe even less money than it would take to rebuild that one to OE spec. My suggestion would be to take it to a qualified tech along with a schematic for a 6550/KT88 Sunn amp and get a estimate to revive it.
I can post or send you a schematic, but they are available all over the web.

[staceyz]

Thanks for the reply & advice..!

[EdBass]

No problem, nice old amp if you can get it squared away. This is a gut shot of a 6/4/71 inspection date 200S, pretty much all of the stuff that isn't in your amp's chassis will need to be there for it to work.

[BC Gearhead]

Hello fellow Sunn worshipers. I picked up this very amp yesterday, and thanks again for the great deal. It’s missing the bridge, filter caps,one input jack,fuse holder,power cord and the power transformer is definitely not original. I’m hoping the correct voltages are present when I have a chance to test. I probably won’t have time to look at it for a while but that amp has found a good home. I have owned a 2000s for 12 years as well as several small wattage vintage tube amps. I think the Sonaro is going to be perfect for the smaller rooms where I occasionally gig. As well as a 1974 Pre Bass I own a 4003 Ric so it might be fun to use both amps for the ric-o-sound output but I probably have to get in shape first to lift all a that gear . I’ll post about the progress as it happens, might be a few months before I get to it and since it’s in very good shape cosmetically for a 47 year old amp I’m going to take my time and do a nice job with the repairs.
Cheers

[BC Gearhead]

 Finally got the amp working. All new eletrolytics and coupling caps, checked all components tolerances, replaced missing jacks and it fired up fine on the variac. The only problem was that the B+ was too high due to the different transformer. I used a power MOSFET with a small wattage zener and a couple resistors to bring things down to non melt down  zone.  I put in an old 12ax7 that tesed very good ,a NOS 6an8 and some Westinghouse 6550?s that also tested good. It was very satisfying to bring it back to life and hopefully it will stay in service for another 48 years.
Cheers

[Isaac]

But how does it sound?

[BC Gearhead]

I have a rehearsal tonight with a full band on bass. I will report later.

[BC Gearhead]

The Amp sounds great. I'm very happy with the results and is plenty loud for my use. It's so much better than the Traynor SB500 Class D head I've been using and so much easier to lug around than the 2000s. It's a keeper. Now I have to figure out if I want to keep the 2000s or let someone else get some use out of it.