SC 120/Hiwatt #4

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Re: SC 120/Hiwatt #4

Postby cyclecamper on Wed Nov 13, 2013 6:45 am

gldtp99, A few years ago I picked up a non-working SC-120. It's pretty rough, faceplates are rather nasty, chassis is badly pitted and has some very rusty spots; maybe some old caps leaked or something on the top of the chassis between the filter caps and the preamp the sockets. Some broken pots, no tubes, no knobs. It should get all new pots and all new caps. But the transformers are good according to the guy I bought it from (I will do an inductance back-voltage test with a battery and light bulb sometime, which seems a pretty good indicator of output transformer problems). And the chassis is already punched. It's a good candidate for a complete rebuild, but it may be years before I even start on it.

I'd like to strip it down to the bare chassis and get the chassis plated before I begin. Of I can give it a powdercoat/baked finish. What would you recommend? Just copper plated tarnishes too easily. A really good chrome job would be nice, like an old Dynaco or MCIntosh. Or the baked black holds up well. Brushed dull nickel plate over copper plate could look nice, and conduct well. What do you think?

I'm a good tech and builder, but not a qualified engineer. I've built lots of kits and done a few rebuilds. I can follow a schematic but I'm not really eager to merge two. But the idea of a powerful really quiet HI-WATT is very very appealing. I'd really like to float the preamp filaments to a higher voltage in ref to the cathodes, and also have DC filaments on the preamp, and anything practical for reducing the noise, like modern low-noise metal-film resistors instead of the "high-MOJO" carbon-comp types, and really good power supply filtering. I'd also like it to be usable for bass guitar occasionally. And a switch to turn off 4 of the output tubes. I have no need for 4 input jacks.

I have variacs, VTVMs, but I sold my 'scope and will get another sometime. I understand the essence of good layout, good grounds, etc. This is a small job compared to building the Heathkit oscilloscope which really had a lot of parts (but the beam drifted off-screen between uses, just not stable like a Tek).

I sure do wish we were neighbors. I don't look forward to accumulating all the parts. But bolting them in, wiring and soldering them up would be fun.

I'm starting a new job, so it might be years before I get to this. Are you sure you don't want to do one more?
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Re: SC 120/Hiwatt #4

Postby gldtp99 on Thu Nov 14, 2013 6:20 pm

You've got some interesting ideas for the rebuild---- but i'm not interested in doing another rebuild/conversion like this------this is a job I think you should do yourself------ the #3 SC120/Hiwatt conversion I did is for sale on ebay:

http://www.ebay.com/itm/281203300929?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

This isn't my auction and I haven't seen this amp since it left my hands several yrs ago----- It sounded very good when it left my hands------ the blob of black tape inside the chassis by the fuseholder isn't my work----- I don't know what that is or why it is there------also an earlier owner added a .047 Mustard bypass cap at the end of the preamp board----I usually leave this cap out to make the amp work better with non-Fane speakers.
Also, I didn't hardwire the voltage switch to 120V---- It had the orig plug (they lost it ?) and was working properly when it left my hands.

Here's a quick vid of #4 SC 120/Hiwatt conversion:

http://www.youtube.com/watch?v=tqLBIkjwlD8

This amp sits in my shop and does nothing but collect dust----- why don't you buy this one instead of converting yours ?
I'd let it go for less than the guy is trying to sell #3 for on ebay...........................gldtp99
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Re: SC 120/Hiwatt #4

Postby Mr. Foxen on Thu Nov 14, 2013 9:17 pm

gldtp99 wrote:You've got some interesting ideas for the rebuild---- but i'm not interested in doing another rebuild/conversion like this------this is a job I think you should do yourself------ the #3 SC120/Hiwatt conversion I did is for sale on ebay:

http://www.ebay.com/itm/281203300929?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

This isn't my auction and I haven't seen this amp since it left my hands several yrs ago----- It sounded very good when it left my hands------ the blob of black tape inside the chassis by the fuseholder isn't my work----- I don't know what that is or why it is there------also an earlier owner added a .047 Mustard bypass cap at the end of the preamp board----I usually leave this cap out to make the amp work better with non-Fane speakers.


That start of with one Partridge and one EV transformer then? Guess a transitional thing, I have one 50 with one of each, wasn't sure if it was replaced.
New music: https://warriorpope.bandcamp.com/album/anchorite
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Re: SC 120/Hiwatt #4

Postby gldtp99 on Fri Nov 15, 2013 7:23 am

Yes, good eye !!! One EV and one Partridge transformer------ it was this way when it came to me and I think both transformers are orig from the factory....................gldtp99
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