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 Post subject: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Mon 11, 2013 9:32 pm 
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Location: Virginia
Been working on this little rig for a few days, resoldering up all the 'iffy' connections and replacing the electrolytics.
Unfortunately, one of the final transistors has a broken lead. -- It is a Motorola MPS-U05.

Found three MPS-U51 transistors in my junkbox. -- Same case style.
From what I can tell, they have similar electrical characteristics and appear to be referenced on the same datasheet.
I'm having trouble telling if they're interchangeable. -- The datasheets are a little sketchy.

Would appreciate any help. -- Thanks !

~ Mitch ~


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Mon 11, 2013 9:45 pm 
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Look for the original Motorola data sheets.

MPS-U05 is NPN 60 volts

MPS-U51 is PNP 30 volts

No, not a good substitute.

Rich


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Tue 12, 2013 12:30 am 
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Rats! -- I just *knew* I couldn't get that damn lucky. :P

~ Mitch ~


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Tue 12, 2013 4:41 pm 
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The additional difficulty is the MPS series is in an old Motorola-style package. More modern packages have the collector connected to the center pin... yours is not.

Rich


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Tue 12, 2013 5:04 pm 
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What lead is broken? If you are lucky and it will be the collector lead--you can pick that off of the heatsink tab on the top or that package.

Pete

A Motorola BD517 might be a good sub???


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Thu 14, 2013 3:43 am 
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Nope.... it's the emitter lead broken off flush. :roll:

~ Mitch ~


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Thu 14, 2013 7:16 am 
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http://www.ebay.com/itm/MPSU05-BY-MOTOR ... 58905b6493

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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Thu 14, 2013 10:46 pm 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
Mitch,

That E-Bay price looks pretty steep. If you have time, you should find some QRP forums and ask there if someone has found a good sub.

Just an idea: you might be able to grind-away the plastic around the broken stub and expose enough to make a connection. I would create a sort of three-lead header, and solder all three transistor leads to that.

Ted


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 Post subject: Re: Heathkit HW-7 Final Output Transistors
PostPosted: Mar Fri 15, 2013 1:00 am 
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Location: Santa Rosa, CA
Can you find a 2N6551? This is in a TO-202 standard JEDEC case. The pins are E-B-C and the tab is C. Should be a decent substitute.

Rich


http://www.datasheetcatalog.org/datashe ... 2N6554.pdf


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