Sunn Sonaro problems

[stumax]

Hey all you smart bass players, I have a sunn sonaro. I think its a late 60's model, it has some jumbo power tubes in it that I am not familiar with. Sooooo, here is the problem. It has NO bass response right now. The bass boost switch does little to nothing, and the bass knob seems to do little to nothing as well. In fact the treble knob dosen't seem to do much, either. Now, I thought these were pretty cool bass amps, was I wrong, or is there something wrong with the amp? Other then the fact that it sounds like a mid rangy bassless fart, it seems to work perfectly. Just for the record I had it plugged in to an 8 ohm 2x15 cab which I have tried with other amps and works great.

Any help would be much appreciated!

[Sartori]

What do the tubes say on them? Anything?

[anderbass]

Your Sunn should have KT88 or 6550 power tubes and give good lower bass response. The Sunn tone knobs work differently than most other amps and it takes awhile to get used to them.

But if you've tried every conceivable combination of knob/switch settings and it still has wimpy bass response, Its probably just finally time for that 42 year old amp to be serviced by a good amp tech.

[edbass]

Originally Posted by stumax

Hey all you smart bass players, I have a sunn sonaro. I think its a late 60's model, it has some jumbo power tubes in it that I am not familiar with. Sooooo, here is the problem. It has NO bass response right now. The bass boost switch does little to nothing, and the bass knob seems to do little to nothing as well. In fact the treble knob dosen't seem to do much, either. Now, I thought these were pretty cool bass amps, was I wrong, or is there something wrong with the amp? Other then the fact that it sounds like a mid rangy bassless fart, it seems to work perfectly. Just for the record I had it plugged in to an 8 ohm 2x15 cab which I have tried with other amps and works great.

Any help would be much appreciated!

Probably, and the first thing I'd look at is filter caps. If they are original, they almost have to be in bad shape.

Originally Posted by anderbass

Your Sunn should have KT88 or 6550 power tubes and give good lower bass response. The Sunn tone knobs work differently than most other amps and it takes awhile to get used to them.

If it’s a 60’s model it should have EL34’s, the Sonaro was a 40 watt amp. In 1970 all of the 40 watters went away and the Sonaro went to solid state rectification and 6550’s.
stumax, if you post a pic of the front and back I can tell you what it is/was supposed to be.

Regardless, it should not be performing as the you are describing.

Originally Posted by anderbass

But if you've tried every conceivable combination of knob/switch settings and it still has wimpy bass response, Its probably just finally time for that 42 year old amp to be serviced by a good amp tech.

+ 1000.

[stumax]

Hey so here are some pics of the thing. My guess is that they are kt88? or the 655o tubes.....not sure though. I have tried every conceivable setting on the thing, the knobs and switches just don't do much... Hopefully these pics come through.

Power caps.... tell me more.

[BluesBear]

Doesn't that tube on the right read 6550 in big white numerals?

[edbass]

I was hoping for a full back picture to get a peek at the transformers, but I'd guess that's a '70 or '71 model. Does it have a rectifier tube?
The grill cloth is post '69, however it doesn't look like the logo plate has the "®" on it though, which would indicate '68 or older. Of course both of these cosmetic features coulds have been changed in the last 40 years.

Originally Posted by stumax

Power caps.... tell me more.

Filter caps. They are used to smooth out the "ripple" created when using a rectifier to convert AC into usable DC for the amp to function. These are generally big voltage electrolytic capacitors and have a finite lifespan, and when they go away it can effect the amp in several fashions; including a lack of power and responsiveness.
This may or may not be the problem with your amp, some filter caps (like some tubes) can last a stupid long time; but IMO it's generally a good idea to replace them as preventative maintenence on an old amp like yours.

With all respect, based on the questions that you asked and the fact that you didn't know what output tubes the amp has, as anderbass posts you really need to take it to a good tech.
You aren't going to find a "silver bullet" on an internet forum that will allow you to make your amp "right" again.