Sound City 120 project

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Sound City 120 project

Postby Rex Everything on Fri Jan 11, 2013 12:43 am

I recently picked up an SC120 that the previous owner had removed most of the jacks, pots and switches and then put it in storage. It was not packed well which resulted in the box needing some repair and torn tolex at the corners but it does have the Partridge transformers. I'm not sure yet what the plan is for this amp. I'm open to suggestions.

Here are a few pictures...

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Re: Sound City 120 project

Postby Mr. Foxen on Fri Jan 11, 2013 2:11 am

Looks a state, shame, because looks like it was once a fairly tidily wired one, as far as those go. The burned valve base is a danger zone, if the black won't scrub off, needs replacing. New pots aren't that hard to fit, but there's some resistors missing to go with them, probably got enough pics for you to figure that easy enough. Rest of preamp looks intact.
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Re: Sound City 120 project

Postby Papa Dog on Fri Jan 11, 2013 3:27 am

Mr Foxen is correct.
That amp has been robbed and seems to have had some issues in it's previous life, but IMHO it is far from beyond saving.
The jacks are standard Cliff jacks, fairly cheap. The volume and tone pots that came with those amps new were, IMHO, rather cheap, and I would recomend CTS pots, and use linear pots for bass, mids, and treble. Since it is an "active" system running them linear, at the mid-point, should give you the same as those three controls "dimed" on most other tone stacks.
Ther would be a ground buss along the backs of the pots and there are some caps missing from there, along with the resistors mentioned by Mr Foxen.
I would recomend replacing ALL the electrolytic caps, especially the power supply filter caps, and replace the rectifier diodes.
They can check good, and still pass AC into the circuit.
Good luck with your restoration or whatever you might decide to do.
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Re: Sound City 120 project

Postby burnout on Fri Jan 11, 2013 8:14 pm

Ha! I bid on that sucker on Ebay ;)

Ended up being glad I didn't win it. I built my last SC ebay grab (I think I got mine for $225 with the head box and all) into an early 70s Hiwatt clone. Lots of good stuff on MHuss' website and here from gltp99 - he's done a few. I wouldn't do it again because I have been getting more friends amps to work on lately - but that being said the Hiwatt clone built with these SC amps sound amazing. I'd build another in a heartbeat but I don't think I'll ever need a louder amp.

120Watts into two 4x12s. OOF. With a proper fuzz (I use an OCD distortion box or a Deviever Hyperion) you are well into the land of sonic heaven and you better have some earplugs!

I know there are those who would encourage you to take it back to stock - but if you have the wherewithal check out Mhuss' site and I can give you my layout for the power section so that you can drive 6 EL34s instead of just 4.
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Re: Sound City 120 project

Postby gldtp99 on Fri Jan 11, 2013 9:36 pm

Amp needs the missing heat shield orig between the output tubes and the row of cap cans-- you don't want to install new cap cans and then greatly shorten their working life by having them that close to a major heat source (six EL34's)---- if this heat shield wasn't important they wouldn't have built one there from the factory.
Also, the toasted output tube socket needs to go--i'd just install new output tube sockets---- sometimes the ground point at each one (pin one and eight) needs attention/clean-up due to corrosion.
These issues need to be addressed (IMO) no matter if the amp is kept stock or converted.
i'll stay out of the "Keep Stock vs Conversion" question on this one- :2cents: ..................gldtp99
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Re: Sound City 120 project

Postby Rex Everything on Fri Jan 11, 2013 11:55 pm

burnout wrote:Ha! I bid on that sucker on Ebay ;)

Ended up being glad I didn't win it. I built my last SC ebay grab (I think I got mine for $225 with the head box and all) into an early 70s Hiwatt clone. Lots of good stuff on MHuss' website and here from gltp99 - he's done a few. I wouldn't do it again because I have been getting more friends amps to work on lately - but that being said the Hiwatt clone built with these SC amps sound amazing. I'd build another in a heartbeat but I don't think I'll ever need a louder amp.

120Watts into two 4x12s. OOF. With a proper fuzz (I use an OCD distortion box or a Deviever Hyperion) you are well into the land of sonic heaven and you better have some earplugs!

I know there are those who would encourage you to take it back to stock - but if you have the wherewithal check out Mhuss' site and I can give you my layout for the power section so that you can drive 6 EL34s instead of just 4.



Thanks for the info and advice.

This amp was never on ebay so I don't think it's the one you are talking about.
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Re: Sound City 120 project

Postby Rex Everything on Fri Jan 11, 2013 11:58 pm

gldtp99 wrote:Amp needs the missing heat shield orig between the output tubes and the row of cap cans-- you don't want to install new cap cans and then greatly shorten their working life by having them that close to a major heat source (six EL34's)---- if this heat shield wasn't important they wouldn't have built one there from the factory.
Also, the toasted output tube socket needs to go--i'd just install new output tube sockets---- sometimes the ground point at each one (pin one and eight) needs attention/clean-up due to corrosion.
These issues need to be addressed (IMO) no matter if the amp is kept stock or converted.
i'll stay out of the "Keep Stock vs Conversion" question on this one- :2cents: ..................gldtp99



I agree completely on the heat shield. I'll have to find one or have one made. I also agree on the tube sockets. My plan was to just replace them all as they are not riveted in so it should be pretty easy.

If I do keep this stock do I have to have all six inputs? I can't ever see using a slave unit......
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Re: Sound City 120 project

Postby gldtp99 on Sat Jan 12, 2013 4:29 am

Here's one option for the heat shield: http://www.vintagehiwattrestorations.com/-- I'm not sure it's an exact match for a SC 120, but it should be very close.
No, you don't have to use the Slave jacks if you don't want to.
A couple of guys stopped over to my shop and demo'd the 120/Hiwatt #4 as a bass amp tonight--- they really liked the tone and the fact that it is practically dead quiet between notes/passages--- they don't have the $$$ for it, though.
Their guitar player was across the hall in the studio re-doing some tracks with a HG Jose-type amp i built--they liked the diode clipper but don't have the $$$ for that one, either---i seem to meet a lot of broke musicians- :(
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Re: Sound City 120 project

Postby Papa Dog on Sat Jan 12, 2013 4:43 am

Rex Everything wrote:
gldtp99 wrote:Amp needs the missing heat shield orig between the output tubes and the row of cap cans-- you don't want to install new cap cans and then greatly shorten their working life by having them that close to a major heat source (six EL34's)---- if this heat shield wasn't important they wouldn't have built one there from the factory.
Also, the toasted output tube socket needs to go--i'd just install new output tube sockets---- sometimes the ground point at each one (pin one and eight) needs attention/clean-up due to corrosion.
These issues need to be addressed (IMO) no matter if the amp is kept stock or converted.
i'll stay out of the "Keep Stock vs Conversion" question on this one- :2cents: ..................gldtp99



I agree completely on the heat shield. I'll have to find one or have one made. I also agree on the tube sockets. My plan was to just replace them all as they are not riveted in so it should be pretty easy.

If I do keep this stock do I have to have all six inputs? I can't ever see using a slave unit......


I am working on having some heat shields made in a local sheet metal shop. They should be available by the time you reach the point of needing one. I WILL chime in on the "stock vs conversion" debate. There seems to be a contingent of haters who despise the Mark 4 pre-amp. The only excuse which I can see for literally destroying what is IMHO a work of art would be if it were totally trashed already.
I believe that if a person wants to build a HiWatt clone, morepower to them. But, to take delight in every SC 120+ which is gutted and then re-made into something else truely makes me wonder. I am far from a "purist", in that I believe that there are issues to be addressed which would make the Mk4 a more stable and reliable amp. But to gut an almost complete and functional amp? I do not get it, and I do not like it. I cannot understand the blatant hatered of an electronic circuit.
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Re: Sound City 120 project

Postby Papa Dog on Sat Jan 12, 2013 4:57 am

gldtp99 wrote:Here's one option for the heat shield: http://www.vintagehiwattrestorations.com/-- I'm not sure it's an exact match for a SC 120, but it should be very close.
No, you don't have to use the Slave jacks if you don't want to.


Once again gldtp is correct.
You do NOT have to use all 6 jacks. In fact, you could get by with one jack per channel.
Were I to decide to "loose" a jack, it would be the "attenuated" jack, as I do not understand the point of them.
The "slave" jack might be better labled as "parallel". That jack, when wired as per the schematic, provides an un-attenuated parallel with the added feature that it lifts the ground from that channel. It is actually for "daisy chaining" the inputs of that and another amp, and lifts the ground to avoid "ground loop" hum.
Makes me wonder if the hum lots of guys seem to have is a result of that jack not being properly grounded?
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"The time has come," the Walrus said,
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Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
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Re: Sound City 120 project

Postby Rex Everything on Sat Jan 12, 2013 5:18 am

Thanks again for all the info and please keep it coming as this goes.

Were the Cliff jacks four lug originally as that's all I've located so far.
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Re: Sound City 120 project

Postby Rex Everything on Sat Jan 12, 2013 5:34 am

A few pictures of the cab

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Image
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Re: Sound City 120 project

Postby Papa Dog on Sat Jan 12, 2013 6:00 am

Rex Everything wrote:Thanks again for all the info and please keep it coming as this goes.

Were the Cliff jacks four lug originally as that's all I've located so far.


Yes. They are 4 lug "switching" jacks.
You have to be careful in wiring them, since if you put the hot lead on the wrong side they wont work.

BTW that cab looks to have been "rode hard and put up wet," but it is well restorable.
There Ain't No Such Thing As A Free Lunch.

"The time has come," the Walrus said,
"To talk of many things:
Of shoes--and ships--and sealing-wax--
Of cabbages--and kings--"
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Re: Sound City 120 project

Postby Rex Everything on Sat Jan 12, 2013 9:35 pm

Papa Dog wrote:
Rex Everything wrote:Thanks again for all the info and please keep it coming as this goes.

Were the Cliff jacks four lug originally as that's all I've located so far.


Yes. They are 4 lug "switching" jacks.
You have to be careful in wiring them, since if you put the hot lead on the wrong side they wont work.

BTW that cab looks to have been "rode hard and put up wet," but it is well restorable.


Thanks!

The cab is rough but with a bit of scrubbing will be presentable. Luckily the corner split/tolex rip is on the bottom side of the cab. I have the back panel as well.
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Re: Sound City 120 project

Postby burnout on Mon Jan 14, 2013 2:58 pm

Re: decision to restore or gut and start over..

Different strokes for different folks. As far as my own gear goes - I am a musician first and tinkerer second. It is MUCH more important to me to have a reliable amp with modern components. My SC was really effed up when I got it. Transformer wires cut, bad solder jobs, etc. I'm so happy with the Hiwatt clone I can't imagine that a SC would be better - but maybe one day I'll find one in decent shape and can find out. Playing through two 4x12s with an OCD and a Deviever Hyperion fuzz, my bones rattle in such an amazing way. This is the AMP.

I suggested the Hiwatt clone because so much of his amp was already scavenged. Let the scavengers have the 'vintage' components. I'd rather not worry about a 40 year old resistor or cap when I'm playing a show.

Hey REX - if you need the 2BA chassis bolts let me know. I have like 12 of them. I'm happy to send some your way. I only needed a few and the place I bought them from made me do a $5 minimum order. Paypal me $1 plus shipping and they're yours!
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