| Transistor help!!!!!!!!!!!! [message #488] |
Fri, 20 April 2001 12:35  |
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Boy, do I need your help! I have a Kustom K250-1 that needs a new transistor. It still has the originals in it with the Kustom part number 007-0000-00. The tech that is working on it is having a problem cross-referencing it for a replacement. It is found on the schematic #PC 5065, and it is also used on the K150-1 and K150-2 #PC 5033. Please help me to find a new part number and manufacturer for this transistor. The amp is popping and crackling.....and I need it fixed! Hope you can help me on this problem! Thanks so much!
Kustom Blues Deb
989-723-6157
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| Re: Transistor help!!!!!!!!!!!! [message #493 is a reply to message #488] |
Sun, 22 April 2001 17:06  |
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Hi guys! Gary has come through with the help I needed. Write this down: the new part numbers are 2N3055. There are used in a lot of Kustoms. "They were used on the 100-200 too. They are used in the output of the amplifier, and also in the power supllies of the 200 series." And, as I said before, they are used in the outputs of the 150-1 and 150-2 as well as the 250-1, and probably others of that series. I found these parts are available from MCM Electronics for 79 cents a piece, and they get cheaper as you buy them in larger quantities. And Gary says to check www.mouser.com. There! That problem solved, onto the next one......
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| Re: Transistor help!!!!!!!!!!!! [message #495 is a reply to message #493] |
Sun, 22 April 2001 22:19 |
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Hi Deb, I remember ET asking me last winter if I had any of the xisters you need. He said that the problem with the replacements if memory serves me is that the xisters need a long lead to get through the mounting plate and the push on connecter. I guess his repairman was looking for long leads to install in the kustoms. I don't remember what series ET was having repaired. ET jmp in anytime and refresh my memory. Don
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| Re: Transistor help!!!!!!!!!!!! [message #504 is a reply to message #495] |
Wed, 25 April 2001 13:52 |
GaryH
Messages: 19
Registered: January 2001
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Junior Member |
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Lead length shouldn't be a problem here, unless you're trying to use a transistor that has been previously installed on a printed circuit board. Check out any 200B power amp board, and you'll see the two 36892 transistors mounted on the left side of the PC board. These are being used as part of the plus and minus voltage regulators for the preamps, and when they're installed and soldered to the board the two leads are cut short, so they don't touch the back of the chassis. If you try to use these as the output transistors on the heatsink mounting plate on the bottom of the amp, the leads are now too short to fit through that press-on connector. A new 2N3055 has full-length leads that will fit in this position with no problems; this is how they are mounted in just about every amp made. It's a good idea to check these transistors and make sure that the screws and nuts that hold them to the heatsink are tightened securely. The 200A PA I got from Ebay recently had a couple that were loose which allowed the transistors to overheat. I found and fixed the problem before there was any permanent damage ( things just got a little hot and it dried out the heatsink grease), but if I hadn't caught it, they would have eventually blown out, along with my speakers. Kustom used nuts with lock washers for these spots so they would stay secure, but years of vibration and travel sometimes takes it toll, especially true for bass heads that vibrate all night on top of the cabinets.
I'll have more replacement cross-references for Kustom transistors soon. GH
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| Re: Transistor help!!!!!!!!!!!! [message #514 is a reply to message #508] |
Thu, 26 April 2001 05:56 |
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Deb, sure clears up the lead issue. I was hoping ET would jump in and refresh my memory on this issue. Great to hear that parts are not a problem. Now if Gary can find replacements for the IC's in the 250 and SC series from the metal front amps, Life will great. Don
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| Re: Transistor help!!!!!!!!!!!! [message #518 is a reply to message #514] |
Thu, 26 April 2001 21:49 |
GaryH
Messages: 19
Registered: January 2001
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Junior Member |
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Hey Don:
I just got the 150-250 schematics from Deb, and it looks like the IC you're referring to is an obsolete part that was originally made by Raytheon and Exar back in the 70's-80's. The Raytheon part number is RC4739, and the Exar part number is XR4739. These have been out of production for a while, but are still around at places that specialize in obsolete parts. A quick search on the web turned up this place:
http://www.bbwelectronics.com/intergCircuits.htm
They're in Illonois and list the Exar 4739 on their parts page; you might give'em a call and see if they've got any in stock.
The 4739 was considered to be a pretty good audio chip back then, but has been surpassed by a number of other parts for a while now.
GH
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| Re: Transistor help!!!!!!!!!!!! [message #519 is a reply to message #518] |
Fri, 27 April 2001 15:16 |
GaryH
Messages: 19
Registered: January 2001
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Junior Member |
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Hi All:
I did a little more poking around, and found that there are other replacements for this 4739 IC as well:
TBA231
UA739
MC1303
LM1303
All the same chip, made by different companies. There is also a replacement made by the big cross reference companies ECG and NTE (both the same company now).
ECG725
NTE725
You might have some luck finding these at a local TV repair shop; they often stock assortments of these brands as generic replacements, and maybe still have some around.
Mouser Electronics (www.mouser.com) shows that they have 4 (!) of these currently in stock. There are no doubt many more of these various replacements around as well.
Wow, I had no idea this was made by so many companies... GH
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