sound city 120 can I fix it?

[telenorman]

Hi everyone and anyone,
         My Sound City 120 needs a bit of attention to say the least. One day I plugged in and all I got was a muffled distortion, hardly audible. Now it just humms a deep, sad humm; Can it be repaired? Will changing all the tubes help? I'm ready to spend but don't know where to start.Can somebody please give me a list of things I shouldn't do cos I'm in another dimension here ( I'm just a dental technician) HELP! :brushteeth:Cheers!

[rafe]

It really could be anything. You have to tell us more, how old is it? It may be a capacitor went bad, could be a tube. A visual inspection of the insides is in order, I don't know if you have caps  on the outside on your amp..You need to know how to safely work on an amp, you can be fatally shocked even with it unplugged, that being said. It does sound like a cap issue. Posting pictures will help too. Doug has a great library of information here on this site and reading up on it will help determine if you can handle the repairs yourself. Although tubes may be needed I wouldn't necessarily start there....

[jjasilli]

http://www.geofex.com/ > -Tube Amp Debug Page > Low power or volume, or volume drops off

[RicharD]

Probably needs a cap job.  I've serviced a Sound City.  It may look like a Hiwatt on the outside, but that's not the case on the inside.

[telenorman]

OK Which caps would you suggest I change first?

[telenorman]

another

[telenorman]

et encore

[telenorman]

one for the road

[Dave]

When people talk about cap jobs, they are generally referrring to electrolytic caps. Electrolytic caps are the big ones that look like soda cans with leads coming out of both ends. They come in various sizes.
The tall silver cans mounted to the chassis are also electrolytic caps, but they are usually 2 or more individual e-caps inside one metal housing and are a little more of a pain to replace.

Dave

[Geezer]

Hmmm.....that is much more "Hiwatt-ish" looking on the inside than my old Sound City Lead 50 ever was!

I agree with Buttery, cap job is 1st order (it at least needs that after ~40 years, unless there is evidence it's already been done recently), then see where you're at after that's complete.

G

[rafe]

That is a lot of Amp  6 el34's. Cap job is like Dave and Gezzer suggested. The four multi cans clamped in on the outside and the big silver one slip clamped inside .....I don't know if you have more I can't tell from the pictures (maybe blue one near silver one)...The other smaller caps should be OK .....But like Geezer said do them first and see how it works....ratings should be right on the cans, Doug should have them here his quality is great,prices good and shipping is quick.....and having this forum is well beyond great service

[telenorman]

Thanks chaps! I'm learning fast with all this help and stuff I'm reading on internet! I've had the amp for 20years now and know the person who owned it before, so I can honestly say that it hasn't even been cleaned properly for at least 26yrs The time has come................

[RicharD]

see attached picture.

That's a much nicer Sound City than the one I worked on.  Components and construction look very Hiwattish but not the wiring.  Joyce constructed Hiwatts are among the finest craftsmanship I've ever seen.  I would say this is NOT a good "first amp I've ever worked on" candidate.  It's fairly complicated.  There's a lot that could go wrong.  Absolutely build a lamp limiter before servicing this amp.  I ALWAYS use a lamp limiter after every cap job and I've serviced a lot of amps.  Do not accept Sound City schematics as gospel whereas they changed their amps up all the time.  If you can't find the exact replacement capacitors, make sure your voltage and capacitance ratings are equal or greater.  Do not go lower.  You can put a 25uF 500V cap where a 20uF 450V cap was, but NOT vice-versa.  Polarity is critical.  the lamp limiter will save your ass if you make a mistake.

[telenorman]

I agree with you that it is probably not a good idea for me to start monkeying around here..........afterall  I am completely inexperienced and that amp doesn't deserve it. I'm going to have to do the decent thing here and leave it to a pro
Thanks for all your time, it wasn't wasted.....yous have probably saved a life
Cheers
                   And if anyone knows someone that  does 'réparations d'amplificteurs' near Poitiers\ Chatellerault in France please leave name and number.

[DummyLoad]

smart man... start small. suggest building a champ/18watt/stout/deluxe or the like to cut your teeth on, so to speak. visit the tube amp library of info - plenty of info and projects there to put and keep you on the right track - if you don't understand something then  ask questions! 



--ISO

[gldtp99]

I agree with you that it is probably not a good idea for me to start monkeying around here..........afterall  I am completely inexperienced and that amp doesn't deserve it. I'm going to have to do the decent thing here and leave it to a pro
Thanks for all your time, it wasn't wasted.....yous have probably saved a life
Cheers
                   And if anyone knows someone that  does 'réparations d'amplificteurs' near Poitiers\ Chatellerault in France please leave name and number.

Great idea to not attempt to service this SC 120 yourself-----i have quite a bit of experience with Sound City amps, mostly 120's and 100's, and they are not for beginners.
Your 120 needs all new cap cans and the bias cap, too----- this is just for starters----- the build quality wasn't all that great on these amps and they don't age well in many cases.
Servicing these amps isn't like servicing a typical Fender/Marshall amp---- your 120 has the infamous active Mk4 preamp that is known to have noise problems even when working properly---- these amps can be frustrating to work on because when the usual "amp service" (cap job, tubes, bias, cleaning pots/jacks/tube sockets/etc) has been done correctly, there is often a great deal of backround noise from the active preamp that can be almost impossible to eliminate ---- there are noise reduction mods on the internet and some have good results with them---some don't.
I've taken to gutting these amps and using the transformers/chassis/head cab to build other circuits such as Hiwatt, Soldano.
I think this amp will cost you a lot of $$$ to try and repair, but will probably turn into a money pit and not be a good sounding amp after you've paid a tech to work on it---you may get lucky and find a tech who can handle this job--- Satamax on the Plexi Palace forum lives in France and has a great deal of knowledge about these amps---i'd take it to him if you are serious about getting this amp fixed. http://vintageamps.com/plexiboard/viewforum.php?f=9&sid=c6454cd21afa7a7404d846db2e8b113f

FWIW---- i recently fixed up my Sound City SMF Tour Series head----a very rare 150 watt channel switching amp that Sound City made shortly before they went out of business---it's even more complicated than a SC 120--this one sounds great now-- Pics:

more pics:http://s46.photobucket.com/albums/f112/gldtp99/Sound%20City%20SMF%20Tour%20Series/

[telenorman]

It must be so satisfying when you finish a job like that! Think I'll put my SC 120 back in the barn for now, shame really but my research left me with pretty much the same thoughts. Better off with a new amp. Fascinating chatting with you lot. Thanks again to all for your time

[telenorman]

Well I put it in a box, closed the box and carried it into the barn. That night I swear I heard the thing squealing,'fix me, I will work'. So yesterday I brought it back out and made some arrangements with a pro. Cap job for starters, then I'll see what needs to be done.
I look at it like this;    if I leave it in the barn it is surely the end for it.
                              I'm not in a rush to repair it so can take my time
                              even if it doesn't sound 'great' after then so what at least it works
                              keeps me busy!
Might be asking for some more advice in the not to distant future!

[rafe]

Personally I think it is pretty straight foward replacing the six cap and cap cans.....And as long as it is discharged properly you will be OK. But the call is yours . I know this much, I took my JCM 800 4104 into a tech and I got it back with new tubes and the same symtoms. I was 140 dollars poorer, with no improvement in the amp. I spent a few months reading and repaired a couple small amps and recapped them and then repaired the marshall. I would rarely if ever need to bring an amp to a tech these days. If it is only the caps you are done, if not you have saved much of your budget to delve further into it. That of course is only my opinion. It is really quite safe to work on these things if you learn safety and follow a few rules...That being said , That is a lot of amp, do you play big venues?  

[telenorman]

I have never played any venues. The amp was being played at venues in Liverpool throughout the  mid 70's to about 83- 84 when it was bought by a friend who then sold it to me for £30. At the time I lived in an appartment and never turned the thing louder than 3 or 4. I now live in the country in France and can play a lot louder without my nieghbors banging on the ceiling. I'm not an astonishing guitarist but with friends we make a good noise and have been talking about doing some 'gigs' in the near future and thats why I want to get the SC in some sort of working order.
I have learnt a lot (and still know nearly nothing I'm sure) about repairing it and was sure I could change the caps myself but I wanted it to have a good going over by someone that knows thier stuff. So thats where I'm up to now. I haven't got a limitless pot of cash to throw at this project so I'll wait and see what he's got to say.He seemed to be impressed by the overall condition and workmanship. If it's not to expensive  I'll do the caps and replace all the tubes. I can only sound better than before!

[telenorman]

Howdy,
Well was I lucky!    decided not to do the work myself for I am but a fool. Found someone to recap my SC 120 and.........not only did he do an excellent job, he handmakes these!  Is this normal in your world? .......I've plugged into these things and never heard a noise like it.          www.myspace.com/vizyamps

[rafe]

that amp looks like it was hard to handle