Sunn sonaro

[Freewill]

I have a sunn sonaro that is now distorting after volume 4, I would like to change my tubes but I'm being told to use 6550 or el34 one is a 12axl and 12au7, which ones are the ones to use?

[Isaac]

Which Sonaro do you have? The original was a combo amp with a 15" JBL and a 40 watt amp. Later models were separate head and cab, still with one 15", but with a 50 watt head.

If you have the 40 watt combo, you'll need one 12AX7, one 67V and two EL34 tubes.
If the 60 watt head, you'll need one 12AX7, one 6AN8, and two 6550 or KT88 tubes.

[EdBass]

Which Sonaro do you have? The original was a combo amp with a 15" JBL and a 40 watt amp. Later models were separate head and cab, still with one 15", but with a 50 watt head.

If you have the 40 watt combo, you'll need one 12AX7, one 67V and two EL34 tubes.
If the 60 watt head, you'll need one 12AX7, one 6AN8, and two 6550 or KT88 tubes.

My 40 watter has, and the 40 watt schematics I have show a 7199 inverter.

[Freewill]

It's the 80W head and separate cab

[EdBass]

80 watt Sunns are just 60 watt Sunns with solid state rectifiers, the audio tubes are the same. What hasn't been mentioned is that 60 watt Sunns also have a GZ34 rectifier tube, which is not present on the SS rectified amps.
If you have an 80 watt Sonaro it's probably a 1970, maybe a 1971 model. A picture of the back of the amp would tell a lot about it.

So, back to the early distortion issue.
Did the amp suddenly start getting nasty at 4, or did it gradually start getting dirty quicker? I know you mentioned on talkbass that a tech went through the amp; do you know or can you find out if the electrolytic filter capacitors were changed, and if so with what? The distortion situation could be a lot of things, including the tubes, but the filter caps are frequently the cause of that type of problem and the stock caps are a bit of a weak point using modern wall currents.

[Isaac]

My 40 watter has, and the 40 watt schematics I have show a 7199 inverter.

Guess I saw a different schematic.

[Isaac]

I have to say that distortion a about 4 is not at all uncommon. In fact, I'd say that pretty much all of my Sunns distort at about 4. It is definitely not, by itself, indicative of a problem with the amp. Because Sunn used linear taper pots as volume controls, 4 is nearly full volume.

[EdBass]

I have to say that distortion a about 4 is not at all uncommon. In fact, I'd say that pretty much all of my Sunns distort at about 4. It is definitely not, by itself, indicative of a problem with the amp. Because Sunn used linear taper pots as volume controls, 4 is nearly full volume.

I sent the poster here from talkbass.com. Of course "distortion" can mean different things to different people, but on talkbass the complaint was that this distortion at 4 was a new phenomenon, which I interpreted as probably some type of component failure.

My suggestion was to go to the "Sunn place" with the questions rather than get jerked around by the plethora of wanna be "Internet amp gurus" that post on talkbass.

[BassHog]

I'm wondering if this might be because it's biased way too cold, crossover distortion I believe it's called.
Also, this amp most likely needs a cap job, that can also cause distortion.

I have both the 40 watt el34 Solarus head and the 60 watt Sceptre head and neither of these distort on 4, they are pretty clean almost all the way up.
They have also both been recapped and biased correctly though.

[Isaac]

Also depends on the input. My stock Ric doesn't start distorting nearly as early as another with Bartolini humbuckers.