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Diode or capacitor that clips to metal transistor board [message #11650]

Wed, 19 August 2009 14:47

jimi
Messages: 46
Registered: February 2003
Location: Redding Ca

Member

It is a very small metal can with 2 clear sheathed leads going to bottom of PC 900 board and it sits in a metal clip. Does any body know of a replacement for this? The leads pulled out of it waxed? bottom end and the #'s are gone.

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Re: Diode or capacitor that clips to metal transistor board [message #11651 is a reply to message #11650]

Wed, 19 August 2009 16:07

jimi
Messages: 46
Registered: February 2003
Location: Redding Ca

Member

It clips on the metal transistor platform on the chassis floor. (Attempt at clarification)-Jimi

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Re: Diode or capacitor that clips to metal transistor board [message #11652 is a reply to message #11651]

Wed, 19 August 2009 17:58

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

The diode is an RCA 1N3754. It hasn't been made in at least 20 years. It's job is to alter the bias to the output stage as the output transistors heat up.

You can try and substitute a standard 1N914 type diode, but you will have to find some way to mount the glass body of the diode so that it is in contact with the chassis.

Use a little heatsink grease to ensure good thermal contact between the diode and the chassis and be sure to watch out for the polarity when installing the new diode.

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Re: Diode or capacitor that clips to metal transistor board [message #11653 is a reply to message #11652]

Wed, 19 August 2009 18:07

jimi
Messages: 46
Registered: February 2003
Location: Redding Ca

Member

Thank you for this info,you guys rock as always! I'll give it a try-Jimi

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Re: Diode or capacitor that clips to metal transistor board [message #11655 is a reply to message #11653]

Thu, 20 August 2009 09:54

C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...

Senior Member

ChicagoBill and Steve, couldn't a metal can transistor in a TO-18 or TO-72 be used as a replacement for that diode? Just use the Base-Emitter junction and cut off the collector lead short. I know the thermal characteristics might be slightly different but it just might suffice. Is the original diode that you mentioned a single or dual diode, 0.7V or 1.4V? That would solve the physical size and lead position issues.
Conrad

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Re: Diode or capacitor that clips to metal transistor board [message #11656 is a reply to message #11650]

Thu, 20 August 2009 12:06

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Yes, a metal case transistor can be used to replace the diode and if fact this morning when I read the post I made a mental note that over the weekend I would try out some type that I have at in stock at home in a amp and report back on Monday with a post.
I did find a surplus semiconductor supplyer that carrys the original RCAs, and I am waiting for a email back on pricing that we all know will be boardering on rape!

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Re: Diode or capacitor that clips to metal transistor board [message #11657 is a reply to message #11655]

Thu, 20 August 2009 12:13

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Conrad:
I would think that a transistor junction would work there as well as any other diode. The original is a single junction (.7 volt) silicon diode.

If there was another silicon diode or transistor that came in that original style case, the replacement would be so much simpler.

I've thought about getting some 1/4" aluminum tubing and building a replacement diode by gluing in a standard glass case diode with some epoxy. Maybe when I get some free time I'll build one as a test and run some heat tests to see how it works compared to an original diode.

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Re: Diode or capacitor that clips to metal transistor board [message #11661 is a reply to message #11650]

Fri, 21 August 2009 06:18

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I was thinking about it some last night and I had this thought as I purused around my shop for what I had on hand to get it done.
Take a TO5 case transistor and tack solder on a 1/16" to 1/8th" thick 3/8ths to 1/2" square of brass plate( which can be found in many hardware and craft/ hobbie shops)to the flat top of the case, than remove the original diodes hold down clamp and make a spacer for it sio it can be stacked and find a longer bolt, nut and some washers( 4-40 I think would be best) to have the clamp be tall enought to hold down the transistor, and of course all the transistors leads would need to be heat shrinked to keep the clamp from shorting to the leads.
Ad some thermal compound, stck it all up and bolt it down and it should be a done deal!
What do you think bill?

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Re: Diode or capacitor that clips to metal transistor board [message #11662 is a reply to message #11650]

Fri, 21 August 2009 06:20

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Sorry, that post should have ended with "add some thermal compound and stack it all up"

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Re: Diode or capacitor that clips to metal transistor board [message #11665 is a reply to message #11662]

Fri, 21 August 2009 16:03

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Steve:
That sounds like way more work than it's worth.

If you use a TO-5 case transistor, why not just push it into the clip as is? The clip should expand enough to hold it. I guess I should measure one and see.

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Re: Diode or capacitor that clips to metal transistor board [message #11679 is a reply to message #11650]

Mon, 24 August 2009 05:50

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

On second thought, I guess a TO-220 type will bolt down easy enough.

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Re: Diode or capacitor that clips to metal transistor board [message #11785 is a reply to message #11650]

Thu, 10 September 2009 02:35

Roboburger
Messages: 1
Registered: September 2009
Location: Atlanta

Junior Member

What a trip. A non-working K100-5 was just dropped in my lap with a broken 1n3754.

I was just trying to see what the conventional wisdom was for the replacement... The NTE cross reference page returned this diode:

NTE 5801 http://www.nteinc.com/specs/5800to5899/pdf/nte5800_09.pdf

I'm gonna look-see over this thread again and see if I can figure out what's up.

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Re: Diode or capacitor that clips to metal transistor board [message #18587 is a reply to message #11785]

Sun, 31 March 2013 12:32

davohilts
Messages: 40
Registered: August 2006
Location: Portland, OR

Member

Just an update, I'm working on a K400 which has two 200 boards in stereo and I replaced both 1N3754 diodes with NTE5801 diodes. Some heat grease on the diode and it popped right into the metal clip and worked fine. I have only tested it on one board as I haven't hooked up the second board because of multiple problems with the transistors.
Dave

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Re: Diode or capacitor that clips to metal transistor board [message #18591 is a reply to message #11650]

Mon, 01 April 2013 07:44

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Let us know how you progress and kepp in mind that if that diode is insatlled wrong or not in circuit the result will be alot of blown out transistors.

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