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5033 bad Q5 [message #9777]

Thu, 23 October 2008 21:29

jlwiley123
Messages: 4
Registered: October 2008

Junior Member

Thanks to help from list members, I have a schematic for the 5033 output board in my K150-5 PA Amp.

I have figured out that Q5 is shorted. This is one of 2 transistors mounted on the board that have somewhat large attached heat sinks. The number from the schematic is 38737, and the number on the case is RCA 38737. I was able to google and find an NTE 129 as a substitution, but this doesn't show to have the attached heat sink. Is the original transistor with the attached heat sink available somewhere, or do I need to buy the sub and cobble up some kind of heat sink?

Thanks

James

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Re: 5033 bad Q5 [message #9779 is a reply to message #9777]

Fri, 24 October 2008 07:06

stevem
Messages: 4747
Registered: June 2004
Location: NY

Senior Member

Hi, that original heat sink can be soldered back onto the new TO39 case transistor at the transistors bottom, but its a PITA.
Mouser electronics carrys star shaped black aluminum slip on heat sinks ( I do not have the part number on hand now) order two of these and stack them with a dab of silicone sealer to hold the top one on as it will need more transistor top left than you have after the first one is on.

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Re: 5033 bad Q5 [message #9780 is a reply to message #9777]

Fri, 24 October 2008 07:09

stevem
Messages: 4747
Registered: June 2004
Location: NY

Senior Member

When you solder the new one in leave the leads long as they too act like a heat sink. Just slip some stripped insulation from small wire( or get some heat srink tubing from the shack) on the three leads so if it gets folded over no shorts happen.

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Re: 5033 bad Q5 [message #9784 is a reply to message #9780]

Fri, 24 October 2008 10:26

jlwiley123
Messages: 4
Registered: October 2008

Junior Member

I found the star shaped heatsinks on the mouser website (part number 532-323005B00) and ordered 4 of those along with the nte129 and nte128 transistors. I don't know that the other transistor is bad, but I figured I should get a replacement just in case...

Thanks for your help.

James

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Re: 5033 bad Q5 [message #9785 is a reply to message #9784]

Fri, 24 October 2008 12:09

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The original generic numbers for the driver transistors of your amp are 40409 and 40410. These were only made by RCA, and have been out of production for years. If you search these numbers, you'll probably find a few companies that still have NOS supplies of these parts.

Up until recently I had a bunch of these that I had from the 70's, but I've pretty much gone through my stash. I have found that if you remove the dead transistor from the heatsink, you can carefully ream open the original hole to fit over the top of the replacement transistor. You want the heatsink to fit snug to the case of the new transistor, so open up the hole very slowly and test fit it as you go. Once the transistor is fitted to the heatsink, apply a little silicon thermal compound to the heatsink and press in the transistor, making sure to align the leads correctly.

Hope this helps.

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