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Replacement transistor needed [message #14231]

Tue, 24 August 2010 11:12

HaenC
Messages: 5
Registered: May 2010
Location: Germany

Junior Member

Hey,

i've got an old A200 Kustom Amp here. One of the output transistors is broken and I need a replecement for it.

The transistor is located at an PC702 power amplifier board, part number Q704 with the numbers 40409 + 38736 on it.

I guess theres no such transistor awailable out there, so I need an other one that fits in there.

I'm happy about every kind of help

best wishes from germany

HaenC

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Re: Replacement transistor needed [message #14233 is a reply to message #14231]

Tue, 24 August 2010 13:53

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

This question comes up here from time to time, so let's recap.

The original driver transistors were manufactured by RCA and were used in many amps including Kustom, Acoustic Control, Macintosh, Heathkit, etc. The generic part number is RCA 40409 and RCA 40410. The transistor is a basic TO-39 part that was built into a small rectangular heat sink. These transistors have not been made since the 1970's. No modern transistor is made with this style heatsink/case combination.

These transistors come up on eBay here in the US every now and then. And a few dealers may still stock them as they were used in a lot of maps back in the day.

The best replacement would be NOS replacements, as they will have the same characteristics as the originals. The next best thing would be to replace them in pairs with a modern equivalent transistor with an add on heatsink. A good replacement for a 40409 would be a 2N5681 and for the 40410 a 2N5679.

You can remove the old transistor from the original heatsink and reuse the heatsink with the new transistor, or just use a new press on heatsink.

I suggest that you replace both of the 40409 transistors on the board with new ones, as the two new ones will share the power more evenly than one new and one old one.

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Re: Replacement transistor needed [message #14235 is a reply to message #14231]

Wed, 25 August 2010 13:58

stevem
Messages: 4744
Registered: June 2004
Location: NY

Senior Member

Hello and welcome from this side of the Atlantic!

Haen, note also that the transistor you need is concidered a driver transistor, as the outputs are the ones mounted to the rivited on aluminum channel on the floor of the amp.

One thing to check when you or who ever works on the amp gets ready to close it back up is that the clip on bias diode in the center of that afore mentioned output transistor bracket is (1) in its clip with some heat sink compound and (2) that the two leads going back to the board are still intact.
These leads have a habit of snapping off somewhat easy after 40 years or service.

How did you come to get your K200?, I can only guess that it is but a handfull of Kustoms in your country!

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Re: Replacement transistor needed [message #14236 is a reply to message #14231]

Wed, 25 August 2010 14:51

HaenC
Messages: 5
Registered: May 2010
Location: Germany

Junior Member

Hi everyone,

thanks for the help, I'll get those NOS replacements I guess - if someone sends it to Germany....those are considered military surplus and you are allowed to ship them to the US only...

But I have some friends in the US, so this shouldnt be a problem.

Well, the K200 is not my personal property, it belongs to a friend of mine who, how else, got it from the US. I have never seen one again here in germany.

Ive heard that is might be some special model, because it has no model description on the back, only a serial number.

Bye bye

HaenC

PS: the "C" at the end is also part of my name, because i what do translate my german nickname into english, so the C stands for the german "hänSI"

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