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K150 blows fuses [message #11029] Tue, 12 May 2009 17:24   natedriver Messages: 35 Registered: March 2009 Member I just bought a couple of k150 combo heads with no chassis one lookes very clean and had a considerable amount of new parts i plugged it in played fine turned on trem vibe and fuse blew. resistor on board where blue speaker wire connects to jack blown,output transistors blown, emitter resistors blown. Havent even got to driver transistors. hooked up inline fuse holder so i can start testing. My round about question is was turning on the trem vibe just enough to blow the power section? I am pensive about putting new transistors resistors etc. put in new fuse and basically duplicate catatrophe. Maybe the amp was on the edge and just needed a nudge so to speak. Alot of new caps on power section board new bridge rectifier new output transistors. the fuse was I beleive original should I check other areas such as transformer output choke I guess just start going over the whole amp. I was playing the amp for less than five minutes through a 1x15 cab I dont know the ohmage of the speaker but would a 4ohm speaker blow all those parts I thought K150 rated about 6ohms? Report message to a moderator

Re: K150 blows fuses [message #11033 is a reply to message #11029] Wed, 13 May 2009 06:26   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member Hi, I do not have any of my schematics here at work with me to try and help you out, but off of the top of my head I can not see why turning on one of the effects would blow the output stage unless something was miss wired by accident or by intent! , or a solder bridge happended.Was this section of the board worked on also? Did both the TO3 outputs and their emitter resistors blow? was the fuse installed over a 3 amp slow blow? These amps where made to run on a 6 to 8 ohm load, and you can run it at 4 if used at mid to low volume because the output stage will run twice as hot at 4 ohms as compaird to a 8 ohm load. Was the amp humming at 120 hz at all which may have indicated a bias problem? Kustoms have hiss, but very little hum. Are both leads on the temp/bias diode mounted inbetween the two outputs ok? I will dig out my schematics for tomorrow morning, but may be Bill could give some input on your problem alsoif he has the time. Report message to a moderator

Re: K150 blows fuses [message #11034 is a reply to message #11033] Wed, 13 May 2009 08:56   natedriver Messages: 35 Registered: March 2009 Member It does not appear that the preamp board was worked on. Both T03 and both emitters blew. The fuses was a 3 amp soldered fuse with a clear plastic tube over it making me think its been there for quite some time. I played the amp just to make sure it was working not loud at all really. No hum temp /bias diode looks good. I actually bought 2 K150s this one which looks pristine inside and another that to coin the term is "barn fresh" so I have a duplicate to compare against parts wise. Some of the caps on the power section board were replaced with polarized electrolytic caps, emitters were new T03s were new drivers look new bridge rectifier is new so im thinking tha maybe this occured before and the root of the problem was missed. I could go through the board and replaced failed parts and see what happens. Any advice would be appreciated. Report message to a moderator

Re: K150 blows fuses [message #11035 is a reply to message #11029] Wed, 13 May 2009 12:25   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member What brand and part number are the TO3s? do they meet the spec for a 2N3055, do they have unsulators under them, and the driver transistors are the original RCA boxed heatsink type, most times part number 38737 and 38736? Report message to a moderator

Re: K150 blows fuses [message #11036 is a reply to message #11035] Wed, 13 May 2009 15:52   natedriver Messages: 35 Registered: March 2009 Member They are 2n3055s the drivers have got grease on them I checked them and they both seem to be blown as well other transistors have been changed on the board and replaced with nte128s insulators are in place Report message to a moderator

Re: K150 blows fuses [message #11037 is a reply to message #11035] Wed, 13 May 2009 15:55 chicagobill Messages: 2005 Registered: April 2003 Senior Member As far as I know, there would be no reason that the power amp would blow up when turning on the FX. My guess is that there was an underlying problem that just decided to show its ugly head when it did. The Kustom power amp circuit is generally the simplest and the most stable design out there, being used by a number of major amp companies through the years. As Steve asked, what parts were used in the earlier repairs? I'd be most suspect of replaced outputs and drivers. If under rated or mis-matched parts were used, it could have been a blowout just waiting to happen. If you are going to work on these yourself, I'd suggest building a light bulb limiter. It will save you a lot of time and money in the long run, and it doesn't take too much to make one. The simplest would be a clip in light bulb socket that replaces the fuse during testing. And in order to get the right schematics, tell us the PC board numbers of the amp. Report message to a moderator

Re: K150 blows fuses [message #11038 is a reply to message #11037] Wed, 13 May 2009 17:32   natedriver Messages: 35 Registered: March 2009 Member My pc board numbers are pc 5032 pc 1400 pc1500 The outputs are 2n3055s The drivers I cant tell but they were replaced and they are blown Ive read in other posts that replacing drivers back into the origanal heat sinks could be problematic any thoughts as to a light bulb limiter are you refering to bulb brightning then dimming as the filter caps charge? and what wattage bulb do you recommend? I do have a second k150 that I can do some side by side eyeballing the bridge rectifier is new and has kbpc2504 part number I think that is a 25amp to 300amp rated according to searching on the internet data sheets can be a little confusing at times Report message to a moderator

Re: K150 blows fuses [message #11039 is a reply to message #11038] Wed, 13 May 2009 18:19 chicagobill Messages: 2005 Registered: April 2003 Senior Member The light bulb limiter is just a 60-100 watt light bulb wired in series with the ac power line of the amp under test. Sometimes they call them fuse savers. If there is a problem with the amp under test, the light bulb lights up and takes up all of the current draw that the amp is pulling, saving the fuse and all of the expensive parts that you've just installed. In our shop we use one when powering up any amp that comes in with a blown fuse. They are not perfect, but they do help. Your amp's power amp PC board contains the low voltage regulators as well as the power amp circuit. I've remounted new TO-39 drivers into the old heatsinks with some success, but I'd probably recommend just using TO-220 cased drivers with small clip on heatsinks. It seems harder and harder to find good small package (TO-39) drivers now-a-days. If you need them, I know that I have a jpg of the 5032 board schematic, but I'll have to look into the pre-amp boards. Maybe Steve has them all. Report message to a moderator

Re: K150 blows fuses [message #11040 is a reply to message #11029] Thu, 14 May 2009 12:59   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member I have to look and see what schematics I have, as those 150 combo models with the choke transformer are a strange mixture of a K100-8 and a metal face k150 head if I recall right! Report message to a moderator

Re: K150 blows fuses [message #11041 is a reply to message #11040] Thu, 14 May 2009 18:21   natedriver Messages: 35 Registered: March 2009 Member I appreciate your help and advice Ill check those transistors that regulate the preamp cicuits as well. Report message to a moderator

Re: K150 blows fuses [message #11042 is a reply to message #11029] Fri, 15 May 2009 06:19   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member Where the emitter resistors 1 ohm 5 watts? I would also check that all the power rail connections on the two big 2500 mfd filter cans are good and tight, also are the two blown 2N3055s a brand name, or just stamped 2N3055 as in made in by some company in China who`s` forte is really making rice noodles! Report message to a moderator

Re: K150 blows fuses [message #11043 is a reply to message #11029] Fri, 15 May 2009 06:24   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member Oh, I do have a schematic for the ps 1400 preamp, and I have a basic two channel K100 non combo head schematic which will give you the 8 volt regulator info and then I have a k150 pc5033 schematic for the driver/poweramp section. Report message to a moderator

Re: K150 blows fuses [message #11049 is a reply to message #11043] Fri, 15 May 2009 22:44   natedriver Messages: 35 Registered: March 2009 Member the emitters were xicon 5w 0ohm 33j if that helps the transistors do have the "s" 2n3055 signature and all to3's are that make connections good to power rail Ill pm you info about schematics Thanks again nate Report message to a moderator

Re: K150 blows fuses [message #11051 is a reply to message #11049] Sat, 16 May 2009 12:38 chicagobill Messages: 2005 Registered: April 2003 Senior Member The emitter resistors should be 0.5 ohm, 5 Watt. It could be that the previous repair person didn't have the correct value. Or they were trying to improve the circuit. Report message to a moderator

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