SUNN Stage Lead power issue

[markorock37]

Picked up a Sunn stage lead for next to nothing. Has power but no sound. Found an open 680K resistor which I replaced. When I powered it up it fried one of the power resistors on the board. I couldn't find a schematic for it anywhere so anyone had any luck with these?

[Loudthud]

The Sunn Stage Lead is extremely rare. Probably only made one or two years. I'm a moderator on the Unofficial Sunn site and there are no known schematics. Let me know if you find one. Probably close to the Alpha or Beta series.

http://sunn.ampage.org/

[markorock37]

So I am finding out. I believe they only made it in 1975.

[markorock37]

This cab has 4 - 10" speakers. One was blown. So I'm on the hunt for one of those as well. I plan on completely restoring this amp.

[Loudthud]

The info I have says the Sunn part number of the speaker is 81-0116-00-90. A 10 inch 16 ohm speaker also used on Beta 410. Speakers might be stamped 0116 on the back if there is no Sunn label. Once in a while you'll see a Sunn speaker on Ebay.

[J M Fahey]

If you find none , and reconing is impossible or 3x the price of a new one,  remember that Jensen makes the *very* good and relatively inexpensive MOD speakers.
Many of them are available in 16 ohms.
The MOD 1050 in 16 ohms would be a perfect replacement.
They are available in incredible 4/8/16/32 ohms.

[markorock37]

Yep there were numbers stamped on the speakers alright. I'll check that tomorrow. I'm gonna try as best I can to keep it original. Thanks for the info!

[J M Fahey]

If possible, post a few close up pictures.
A front one, a back one and some closeup of whatever inscriptions it might have.
It was probably OEM made for them by Eminence or CTS or Pyle.
I guess Jensen was out of the picture by then (they were getting heavily into car speakers) .

[markorock37]

[J M Fahey]

1) your speakers have no manufacturer´s codes (unusual) but show, as loudthud said, Sunn´s own internal code.
They have Alnico magnets (which were dropped everywhere between 1973/75 ) so in theory you shoud have it reconed (ask Ted Weber) although if too expensive or inconvenient, replace it by one of those I suggested earlier.
The amplifier board knows nothing about magnets.
Anyway keep the blown speaker frame, maybe in the future you change your mind.
2) from what´s visible in your slanted picture, the power amp has a driver transformer.
Please take a new one "from above" to see the entire board and how many power transistors it has, to compare it to better known models.
*Maybe* the power amp matches something .
Also show a closeup of the burnt area.
Just shooting in the dark.

[J M Fahey]

*Maybe* your power amp matches or is somewhat close to this Sunn Studio Bass

[markorock37]

Best pic I have at the moment, top right corner of the board just left of a ceramic resistor are two brown resistors. The one on the bottom of the two went up in smoke. Thanks for the schematic, looks similiar.

[markorock37]

Definitely keeping the speaker. I'll try to find a replacement but I will get it reconed if I have to. I'm sure this will be worth more in the long run if I keep it as original as possible. I do know those speakers sound good!

[markorock37]

The burned out guy is a 33 ohm 10%, is it safe to say a 5W will be sufficient?

[J M Fahey]

No, because *someting else* is burnt.
First repair that.
I´m quite sure the schematic reasonably matches the one I posted, with maybe a couple different values to account for the higher power (which means higher rail voltages).
That 33 ohm you mention probably is a 1/2W or at most 1W resistor, no more.
Your output transistors are probably blown, check them for shorts.
Search the Forum, it has been explained lots of times.
Also build a series lamp limiter (search it too).
Beware that Resistors R142/142 , labelled 33 ohms, are really 0.33 ohm ones.
I *hate* when they drop the leading "0" , which makes it easy to miss the dot.
The better European system is to use a letter to indicate the dot, so 0.33 (or even worse:  .33) ohms is written as 0R33 ; 1200 ohms is written 1K2 (instead of 1.2 K which might be misread as 12K if you miss the dot, specially in a photocopy or poor scan)
Oh well.