Filter Cap ??

[retrorod]

Hey, On the 120 watt amps....What is the 1000uf@35-80V capacitor re-placeable with? I can,t seem to find that value from my suppliers? I am still having problems with the 1000S in dropping out in volume and giving a distorted sound...I have replaced the main power supply caps and am looking further into it. Could weak or faulty rectifier tubes cause this loss? Thanks, Rod

[loudthud]

A 35V or 50V part will get the job done. That cap is protected by a 22V Zener diode. Have you replaced all the tubes including the 6AN8A? A bad tremolo "bug" might cause a volume drop. No replacement known. You would have to install a jumper wire across the Cds cell and then see of the problem goes away.

[retrorod]

Thanks, Could you explain 'across the Cds cell'? I am ordering a 6AN8A in case that is an issue...Thanks, Rod

[loudthud]

The tremolo "bug" consists of a low voltage light bulb and a Cadmium Sulfate photo cell (a light dependent resistor) in a light tight enclosure. It's a black block of plastic near one corner of the circuit board. The tremolo oscillator is connected to the light bulb, the CdS cell is in the guitar signal path right before the volume control. There are two coax cables that go from the preamp over to the circuit board. I would just solder a wire from the clockwise terminal of the volume control over to the end of the cap where the other coax is connected.

The only layout of the trem-reverb board I can find is the newer 190L-350L version. The Sunn part number is 32-0044.

Edit: Below is what I have for the 190L-350L Vibro board and the 190L schematic.

[retrorod]

Thanks alot, loudthump for getting the layout diagram. You are "the man". It looks like a totally fifferent animal than the board on the '69 1000S. Don,t think it will help me, unfortunately...Rod

[retrorod]

"I would just solder a wire from the clockwise terminal of the volume control over to the end of the cap where the other coax is connected."
Hey Loudthud OR "Loudthump" as we say in my part of the country! I want to thank you 'wholeheartedly' for your help!   I finally wrapped my brain around the jumper suggestion and YES...I am back to full power on this amp. I was hoping that the trem Cds was not bad...as I was really liking the (intermittant) trem that I was getting before the amp started really screwing up. I had to troubleshoot the reverb on this amp also. At least I have that working again.
 Will this jumper 'fix' be sufficient or is there a 'better' permanent fix? Thanks again, Rod
 

[loudthud]

The jumper was an experiment to see if the problem is caused by the tremolo circuit. Anything that would cause the light bulb to go off could be the source of your problem. The fact that it works part of the time suggests that it's not the tremolo "bug" which most likely would fail completely. The most likely cause is the Depth pot being intermittent. A good spray of Deoxit should fix that. Other possibilities are a broken wire or a solder joint somewhere, especially on the circuit board.

Remove the jumper, play the amp untill it fails, then twist the Depth pot to see if you can bring it back.

[retrorod]

Thanks, I,ll work on that again tomorrow..Rod

[retrorod]

Hey Loudthud, I am getting back to amp later than usual. Had a work meeting this afternoon. Anyway, I cleaned up around the depth control(deoxit) and re-soldered a few leads on the pcb and did some continuity checking...took the jumper off and evrything seems to be OK.. I have the gain, the trem works, although it is slow to start and works only through a limited amount of potentiometer rotation. I can kill the trem with a dummy plug in the footswitch. Am giving it the longevity test now...!!! I am still skeptical about the pcb board though. There was some earlier repair work done there at some point.
 Can I please clarify what schematic is the closest to this 1000S? This is a 1969 dual rect. with trem and verb. I have been comparing to the 100S schem. Is there a scematic that is more near to this amp?  I am using the 100S w/reverb schematic. Does this accurately show the components of the trem-rev board of my amp? I don,t see that zener diode that is across the 1000mfd cap. It looks like that was replaced on my board as well as a couple 1K res. that I don,t see on the 100S schem. In your experience, how often is the 1000mfd cap bad? Thanks again, Rod

[Soundmasterg]

Rod, if that 1000uf cap is more than 10 years old, I'd just replace it. I picked up a 1000uf 50v radial cap the other day for $2.50 or something brand new, and an axial cap wasn't much more than that, and that was a retail price at a local store. If you replace the cap and you still have a problem, then you know it isn't the cap, but you also know that cap will be good for a long time. My 2 cents....

Greg

[loudthud]

There are a lot of missing Sunn schematics. The most common one available that is close to your amp is the 1200S dated 12/18/71. It has mid-boost and is solid state rectified. The version at Schematic Heaven has page 2 with shows the layout for the trem-rev board. It looks a lot like the 190L/350L board.

http://www.schematicheaven.com/newamps/sunn_1200s.pdf

The only other 120W amp schematic commonly seen is the 2000S with Bassboost from 1969 (no exact date except it says after 5-10-69). It is tube rectified. I've never seen any other schematics from the 1000S series. I have a 1968 1200S that doesn't have tremolo or reverb. Never seen a schematic for that one. I suspect it's somewhere between the 100S without reverb and the 2000S.

[retrorod]

Thanks Loudthud! I will get back with ya...Rod

[patlaw]

Regarding the SM-1, has anyone done a voltage-versus-resistance profile of a working unit?