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Blown 250 Bass Amp [message #11409] Sat, 11 July 2009 10:56   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member I took my K250 - 1981 model - out of 4 or 5 year resting mode and was going to use it for a county fair gig. Turned it on at home and ran a few bass scales - worked fine - including the infamous Kustom hiss. Went to band job, setup with a DI box to run with house sound system, about 2 minutes into opening number, amp went dead and smoke poured out of the head. Opened up the amp head when I got home. There is a PC board mounted to the bottom of the amp, and has red and black wires feeding it from two large (what I think) are capacitors. This board has several transistor or resistors that are burned or burst open. From reading posts on this forum, it sounds like some of you are electronic experts and know how to repair these wonderful amps. Is there someone who works on these for a living or for hire? I really want this baby fixed if at all possible - I have owned it for 25 years and it is in almost brand new condition. To me, it's worth spending some $$ to get it going again. I might also mention, the lower channel..not the selectone one...has had almost no output for several years...you have to turn it almost full open to get any sound out of it...Just the top channel was fully functional. Report message to a moderator

Re: Blown 250 Bass Amp [message #11412 is a reply to message #11409] Sat, 11 July 2009 15:27   pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi Senior Member I'm no tech, but I've heard some other guys saying that a direct box with the older K200 have fried pre amp boards because the mixer was on the other leg of the 220 distribution box. I'd suggest a couple of things. The power amp board is a PC5056 which I believe they used well into the hard tolex covered amps. I see some of the monitor amps on craigs list and Ebay quite often along with the X stereo power amps. They are the rack mount versions and if bought cheap enough, just swap out the entire board along with the power transistors. On the bottom channel being weak for a long time, I'd clean the plug that the circuit boards connect to. Kustom had a lot of problems with the plugs and suggested that dealers cut them off and solder the wires direct to the boards. Good luck with it. Don Report message to a moderator

Re: Blown 250 Bass Amp [message #11414 is a reply to message #11409] Mon, 13 July 2009 06:18   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member Hi, Any tech in your area who has done repairs on SS output stages should have no problems repairing yours and price wise even if you where to repalace all the transisitors in the output stage you would still be into it for less than 30 buck in parts. Let the tech know that you want all 4 outputs (T03 transistors) replaced with two matched pairs, like NTE181MP sets.The nte181 has more gain and a higher current rating then the common nte131 replacement! Reapiring the bad preamp/channel may be a different story as most times if the problem is not the slip on Moldex connector to the board, its the 14 pin ECG 725 IC chip on the board. These can only be had now from surplus/new old stock supplyers. Just last year I bought 6 my self at a price of near 18 dollars each with out shipping when two years before they where 3 and change each before they went NOS! I had my one of my k250 blow at a gig once and I now carry a spare head with me as when a semicondutor in a circiut is gonna blow you get no warning. Its also a good idea with SS gear to power them off of a good rack mount type surge suppressor/ limter as SS gear is far lees forgiving then tube gear to power surges, also these amps where not made as late a 1981, I guess you mean you bought it then. Any way let us know how you make out with it. Report message to a moderator

Re: Blown 250 Bass Amp [message #11417 is a reply to message #11409] Mon, 13 July 2009 09:54   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member Thanks for the update, Steve. Previous to my acquiring this amp (I got it in 1985), I think someone may have written their name on the inside on the main plate as an anti-theft ID mechanism. It is signed "viera 12/11/81"....or it may have been worked on before I bought it and the technician could have signed it...who knows? I see on that main output board some of the ports where the different colored wires connect have been labeled with a fine tip marker R, G, B, etc. BTW, is there a reliable way to date these amps? One other question ..I play a Peavey Dyna-Bass with active electronics on board...is that little bit of preamp boost harmful to these old amps? I played that bass thru the Kustom for quite a number of years before I downsized to a smaller amp. I'm just wanting to make sure I haven't caused the failure...or...is it just due to the age of the equipment. I know anything can break/fail at any time. Report message to a moderator

Re: Blown 250 Bass Amp [message #11419 is a reply to message #11417] Mon, 13 July 2009 12:09 chicagobill Messages: 2005 Registered: April 2003 Senior Member John, welcome to the place. My take on the situation is that your amp is repairable, and as Steve sez, any tech with good solid state skills can get it up and running again. The usual problem is that a lot of young techs look at the power amp board and go "What the heck are those things?", referring to the driver transistors that have been out of production since the 80's. And so rather than figuring that this is just a solid state amp like any other Peavey or Fender or Crate, they may tell you that they can't or won't fix it because they can't get parts for it or some other excuse. I don't know what your tech situation is out there, but it might help if you find an older tech who has seen one of these before. Worst case, is that you could ship it out to have it repaired. Pleat's idea of buying a donor amp is also a reasonable approach, as the basic 250 power amp board was used in a lot of Kustom amps. And if you do the work yourself, you can save some cash as well. The only down side I see to this is that the donor amp is still 30 years old and could also be nearing the end of its life cycle. The pre-amp chip problem can be handled in a few different ways. You can find a NOS one or a used one or the board can be adapted to use a modern replacement chip. But before checking the chip, I'd do as Pleat suggested and check the plug on wires. That pre-amp board has a plug that connects the circuit to the Fuzz FX board. If you don't have the Fuzz FX in your amp, there is a jumper plug that must be installed or the signal will not pass through the circuit. From your description of the loss of signal, that would be the first thing that I would check. As for dating your amp one of the members here, Les Strickland, has decoded the factory secret codes and has posted a serial number list. If you know the serial number of your amp, his list will give you an approximate date of manufacture. Report message to a moderator

Re: Blown 250 Bass Amp [message #11420 is a reply to message #11409] Mon, 13 July 2009 12:21   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member I have many active basses(1 9volt battery) and they do not over load the number one input on eitheir channel, but my 18 volt Carvin bass I only use in the 3 db down #2 input, not that it will blow out the preamp but it does have plenty of drive to clip the preamp(s) faster when played hard or slapping. Report message to a moderator

Re: Blown 250 Bass Amp [message #11424 is a reply to message #11419] Mon, 13 July 2009 22:28   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member Thanks Bill !! In reading, I find that Les has left the forum, but no big deal. I just know it is a Kustom from way back when, and these amps were THE AMP to have on stage. My serial number is 81443...probably one of the last true Kustoms to come out of Chanute, KS. Report message to a moderator

Re: Blown 250 Bass Amp [message #11425 is a reply to message #11409] Tue, 14 July 2009 05:52   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member The tech who works on your amp can help you date it, as the pots, the main filter caps and the power transformer are all date stamped, the serial number will drop you in a range of about 6 months of the amps birth, while these other items can pin it down much tighter. There is also a production code on the top frame of the amp. Report message to a moderator

Re: Blown 250 Bass Amp [message #11427 is a reply to message #11425] Tue, 14 July 2009 08:08   LesS Messages: 477 Registered: December 2002 Senior Member Hi John, SN 81443 is from about 2/15/72 plus or minus a few weeks. K250's were made from about July 1971 (SN 735xx) to Jan 1974 (SN 1117xx) -Les S Report message to a moderator

Re: Blown 250 Bass Amp [message #11428 is a reply to message #11409] Tue, 14 July 2009 09:53   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member Thanks much to all for the answers and help! I am really glad to know that I'm not the only 1960s musician that still loves this old equipment. Now, to just find a really nice old Kustom PA..... Report message to a moderator

Re: Blown 250 Bass Amp [message #11429 is a reply to message #11409] Tue, 14 July 2009 12:12   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member I have a black PA head in a number 7 condtion, but it has no stand, but theres a guy on ebay who has a bunch of stands the you would just need the two colume speakers. Report message to a moderator

Re: Blown 250 Bass Amp [message #11430 is a reply to message #11409] Tue, 14 July 2009 17:46 BC Messages: 583 Registered: March 2000 Location: Kentucky Senior Member Yeah, Don...been there and done that. Some dorks with a sound company blew one of my 200 preamps about 8 years ago trying to force me to go DI when I wanted my vintage amp miked. Luckily Terry was there and encouraged them to mike the amp before they blew the other channel and he would have to pull me off someone! It can happen. Sound men....the scourge of the music world! BC Report message to a moderator

Re: Blown 250 Bass Amp [message #11431 is a reply to message #11430] Tue, 14 July 2009 21:54   pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi Senior Member I've seen a lot of so called sound men drop a 100' snake and the amps are plugged in at stage area, and then they find a wall outlet near the mixer and just plug in the nearest outlet. Lots can happen if the wall outlet is on the other leg of the 220 coming into the building. Don Report message to a moderator

Re: Blown 250 Bass Amp [message #11433 is a reply to message #11431] Tue, 14 July 2009 23:08 BC Messages: 583 Registered: March 2000 Location: Kentucky Senior Member My playing experience has been that there are far more sound men who do not know what in the world they are doing than ones who do. A good sound man is a treasure! I have found a few. BC Report message to a moderator

Re: Blown 250 Bass Amp [message #11438 is a reply to message #11409] Fri, 17 July 2009 22:58   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member Well some fairly good news....the guy who does a lot of the commercial work around here says, get me a schematic, and I'll give it my best shot. So...if anyone out there has a copy of the schematic for this amp...give me a holler....he probably only needs the schematic for the power amp board. I read about the hard drive crash with all the data on it...was there a backup copy made somewhere? What happened to that particular drive? Was it saved or tossed? There are companies who do all kinds of data retrieval from damaged, crashed, burned, extensively damaged drives. Report message to a moderator

Re: Blown 250 Bass Amp [message #11439 is a reply to message #11438] Sat, 18 July 2009 12:52 chicagobill Messages: 2005 Registered: April 2003 Senior Member John, if you pm me your email address, I'll scan and send a pdf of the power amp board and if you need it the pre-amps as well. To be safe, you should confirm the PC board numbers so that I can be sure to send the correct schematics. The power amp board in your amp should be a PC5065. Report message to a moderator

Re: Blown 250 Bass Amp [message #13087 is a reply to message #11409] Thu, 04 March 2010 00:41   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member I am just now getting around to seeing about getting my K250 repaired. I had done some internet searchs for some of the individual components (transistors, etc..) but haven't had great luck. I have located a Kustom 400 lead amp...to use as a donor amp if the Power board is the correct one...did that head use the PC5065? Report message to a moderator

Re: Blown 250 Bass Amp [message #13089 is a reply to message #11409] Thu, 04 March 2010 06:20   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member No, the output board is different, although most of the transistors are the same. All the transistors, FET type transistors and 14 pin Texas Instruments IC chips can still be had to fix these amps although the original RCA brand transistor types will only be found as suplus NOS, just like the 14 pin IC chip is. I can email all the schematics you will need but for the effects board in the -4 model K250. Report message to a moderator

Re: Blown 250 Bass Amp [message #13091 is a reply to message #13089] Thu, 04 March 2010 09:54   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member Thanks, Steve. You had emailed the schematic last year, so I am good on that part. I am thinking that the repair shop will have a lot more knowledge of where to find all the bits and pieces to repair the power board than I can find on the 'net. I think if I were a young, inspired electronic engineering student, I would figure a way to re-manufacture these boards and sell them to us old time die hard musicians! Even tho some of the original components are no longer available, the input-output-ohms-resistance-watts values are known and can be achieved with a different circuit design. I think I will take the amp to the shop, with the schematic you provided, and the parts list cross reference from this website and see if they can do me some good !! I miss playing that amp! Report message to a moderator

Re: Blown 250 Bass Amp [message #13092 is a reply to message #11409] Thu, 04 March 2010 12:14   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member Actually the output stage toplogy for these amps that started in the K200B model was way ahead for its time and is still in very wide use today. About the only big advancement that has taken place is now the whole 100 watt output stage is down to the size of a US dollar coin, and that size reduction only seems to make them for failure prone if you eask me. About the only up grade these vintage amps could use is a soft start circuit which is really not that hard to add in. Report message to a moderator

Re: Blown 250 Bass Amp [message #13093 is a reply to message #13092] Thu, 04 March 2010 15:37   John Hylton Messages: 18 Registered: July 2009 Location: Salem, Oregon Junior Member I know. Look at the size of some of the new Carvin and MarkBass heads...they weigh 5 or 6 pounds and are ridiculously small.. Is there a written chronicle of the old Kustom company anywhere? I've never read why they went out of business...was it change in business climate or poor sales, the economy ? I just never knew what happened to that product. Report message to a moderator

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