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 Post subject: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Sun 26, 2017 4:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 216
Location: Vermilion, Ohio
A friend has asked me to to try and repair his HK SC440 R/P Combo from about 1967. He's sending it to me via a friend from Fl here to Ohio, so I don't have it in my possession yet.
He took it to a shop some years back and they lost the output transistors while trying to locate replacements. I'm coming up empty as far as service info at any price.
Can anyone point me to a schematic, manual or even just a number for the output transistors? There's nothing in Sams. I found 1 currently for sale on the auction site, and a couple of old, dead posts about this unit on other forums. That's pretty much it for the Internet. I can see why the shop may have had trouble finding the parts.
Any help is greatly appreciated.


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 Post subject: Re: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Sun 26, 2017 3:53 pm 
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Joined: Aug Sun 23, 2015 6:01 pm
Posts: 529
Location: South Jersey East of Philly
That one on eBay has a shot of the back with the transistors visible. Write the seller and ask if they could give you the info off them?
https://www.ebay.com/itm/Vintage-Harman-Kardon-SC-440-Strataphonic-Music-System-Fully-Functional-Nice-/122525380210


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 Post subject: Re: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Sun 26, 2017 10:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 178
Location: Arlington, TX, USA
Pretty sure these are going to be 2N2147 or similar which is a TO-3 germanium power transistor with a relatively high fT (200kHz). I think the NTE part is NTE121 on that. The problem with many amplifiers using these devices is they are run so close to their maximum limits just to get a respectable amount of output power. Also, the slow blow fuses normally used to try to protect the outputs against shorted speaker terminals tend to survive, instead resulting in damaged transistors.


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 Post subject: Re: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Sun 26, 2017 10:56 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 1558
Location: Vancouver Island, Canada
https://www.manualslib.com/manual/27933 ... tml#manual

No, the manual is not very helpful, just fun to read if you have the time.

I looked up the March 1968 article in Popular Mechanics, page 92, but besides a small chart of specs, and a grainy pic, there was nothing but general blabber about the new compact stereo systems.

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Last edited by westcoastjohn on Nov Sun 26, 2017 11:12 pm, edited 1 time in total.

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 Post subject: Re: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Sun 26, 2017 11:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 216
Location: Vermilion, Ohio
Tbirdkid wrote:
That one on eBay has a shot of the back with the transistors visible. Write the seller and ask if they could give you the info off them?
https://www.ebay.com/itm/Vintage-Harman-Kardon-SC-440-Strataphonic-Music-System-Fully-Functional-Nice-/122525380210


Ya know, sometimes I'm not the sharpest tool in the shed. I even enlarged that picture trying to read the printing on the transistors. I never thought about asking the guy. LOL.

Thanks Erich. I think I may have a couple of ECG or NTE-121s in my stash, the number is very familiar. If all else fails, I can give them a try on one channel and see what happens.


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 Post subject: Re: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Sun 26, 2017 11:11 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 216
Location: Vermilion, Ohio
westcoastjohn wrote:
https://www.manualslib.com/manual/279330/Harman-Kardon-Stratophonic-Sc4.html#manual

No, the manual is not very helpful, just fun to read if you have the time.


Thanks for that one, though. I didn't see it on the manualslib.com site last night. I'll print it out and put it into a folder for him. I'm sure he will enjoy it.
I see they have it listed as an SC-4. I'll do a little searching for that number.


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 Post subject: Re: Harman-Kardon SC440 Stratophonic info needed
PostPosted: Nov Mon 27, 2017 12:17 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 216
Location: Vermilion, Ohio
The Ebay seller just sent me a close up of the outputs. They are 2N2836, which crosses over to an NTE-121.
Thanks for the help everyone.


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