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Slant face K150-1 thernal shutdown [message #5260] Sun, 02 January 2005 15:49   jbreher Messages: 11 Registered: January 2005 Junior Member I am repairing a friend's K150-1. The thermal switch on the output Q heatsink is shutting the AC down after a couple minutes playing time. Kicks back in a minute later, only to shut down again a couple minutes after that (ad nauseum). I put a meat thermometer on one of the mounting screws for the thermal swich. It cuts out at 120 F, and back in at 119 F. This seems like a low trip point. Anyone know what temp this should kick in at? The bias diode is clipped to the heatsink with what looks like a 3AG style fuse holder clip. Is this the normal means of thermal transfer from the heatsink to the bias diode? Anything else I should be considering for the source of this problem? Lastly, I have schematics and layouts for the two preamp boards, and the layout for the driver board. I could really use the schematic for the driver board and power supply sections. Does anyone know where I can get a copy? TIA, Joe Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5266 is a reply to message #5260] Mon, 03 January 2005 15:27   stevem Messages: 4736 Registered: June 2004 Location: NY Senior Member Hi, the 2n3055 output transistors are the norm for kustoms,they are rated for a max temp of 200 degrees C, or about 390 degrees F according to the specs for the transistor that I found, and the temp conversion chart I used. That termal cut out swt is bad. If you go to thre mouser site with the part number off it they have a cross ref to use and determin what brand and part number they stock a replacement in. That bias diode in the clip is the stock set up, just make sure the diode fits good in the clip and it has some white thermal compound still on it.If this is a metal face 150 I have a schematic for the output and driver board of a 250, it is most likey the same as the 150, but for the extra transistors and resistors that you do not have. If you need a copy, send me a self adressed stamped legal size envelpoe to steve magnotti p o box 1160 yorktown n y 10598. If you need to replace both outputs order NTE 130MP ( I think thats the part number) from the mouser site, these are a matched pair of them. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5272 is a reply to message #5266] Mon, 03 January 2005 19:46   jbreher Messages: 11 Registered: January 2005 Junior Member Steve - SASE winging your way (along with copies of what schemes and layouts I do have). Thanx for the offer. Yeah, I thought that temp point was wrong. I couldn't find any cross reference utility on the Mouser site. FWIW, the part is marked with 'ELMWOOD SENSORS' and '2455', molded into back surface, and has '73D L185 98-4' printed on side in white ink. It would appear that Elmwood Sensors is now a division of Honeywell, and that their 2455 series has been discontinued. I emailed the company for info on the failed part - we'll see what info I get. Google turned up a discussion of other 2455 series sensors, where the middle part of the name 'L185' is surmised to indicate off at 185 F. This seems rational for output Q's. So the RCA 36892 is just a 2N3055? that'll make finding replacements dirt simple (Joe says , as he rummages around in his spare parts box...) I'll post again for the record when this is all resovled. Thanx again. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5276 is a reply to message #5260] Tue, 04 January 2005 08:40   stevem Messages: 4736 Registered: June 2004 Location: NY Senior Member Yes, or a NTE130 for singles, or NTE 130MPs for a matched pair, or NTE181 I think it is for a higher wattage TO3 case type. I think I recall using GE14s a couple of times in the foggy past, they worked well. Some times you can still find old stock of them. But double check me on that GE number, that may be the GE number for the ICs used on the preamp boards for the 150s and 250 and 300/ 600 series. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5277 is a reply to message #5260] Tue, 04 January 2005 08:48   stevem Messages: 4736 Registered: June 2004 Location: NY Senior Member Yea, and 185 degress F sounds more like it.You will need to get some slip on TO5 style heat sinks for any of the drivers on the 5056 board, but I have seen(although I can not find my catalog right now) in the mojo tone parts list the original type RCAs with the intergral heat sink. The 4 lead metal case item on the one preamp board is a common FET, but I am at work now and can not recall the replacement #. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5279 is a reply to message #5277] Tue, 04 January 2005 11:38   jbreher Messages: 11 Registered: January 2005 Junior Member Well, if the thermal switch does the trick, and the amp benches at full power for a couple of hours after that, then I guess my job is done. Then all the speccing of Q's is just so much water under the bridge. We'll see. BTW, what sort of output should I see from this (RMS watts) at onset of clipping? Unit says 6-8 ohms on the back - I guess I'll be testing it at 8. Joe Liberty in my Lifetime! http://q-music.com Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5280 is a reply to message #5279] Tue, 04 January 2005 12:08 chicagobill Messages: 2005 Registered: April 2003 Senior Member Joe: How hard were you were running the amp before it shuts down? I've never worked on a 150, but all of the 200's and 250's I've seen, rarely get hot under normal playing conditions. As for power output, the story goes that the model number is the peak power rating (double the RMS). So a model 150 should be somewhere around 75 watts. I'd be interested to here to hear what your results are. Bill Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5281 is a reply to message #5260] Tue, 04 January 2005 12:55   stevem Messages: 4736 Registered: June 2004 Location: NY Senior Member With 117 to 120VAC and a 8 ohm load resistor, and a 1k input tone you should hit the 70 to 75 watt mark before it clips and about 24VAC on the output. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5284 is a reply to message #5281] Tue, 04 January 2005 14:51   jbreher Messages: 11 Registered: January 2005 Junior Member Don't have to run it hard at all. It'll cutout at bedroom levels. Though I haven't tried it, I doubt I need to run a signal through it at all to get it to cut out. As I noted, heatsink is only at 120 deg *F* when the thermal switch cuts it off. Further hard info: Spoke with rep at Honeywell. Did not recognize 2455 without suffix. However, part number indicates Open On Rise @ 185 F. Digi-Key sells Cantherm thermostats that look to be form fit and function compatible. Rated in C. 185 F = 85 C. Cantherm pn R2008525, Digi-Key pn 317-1087-ND, $6.60 ea. Mouser sells Stancor thermostats that look to be form fit and function compatible. Rated in C. 185 F = 85 C. Stancor pn STO-190 Mouser pn 802-STO-190, $4.14 ea. Ordered part from Mouser. Should be in by Friday. I'll let all y'all* know how it works out. May be Monday before I post - gig this weekend. Joe Liberty in my Lifetime! http://q-music.com * I'm told that 'all y'all' is Texan for 'y'all' - 'y'all' indicating the singular in Texas (evidently plural everywhere else) Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5285 is a reply to message #5284] Tue, 04 January 2005 15:15 chicagobill Messages: 2005 Registered: April 2003 Senior Member Joe: I'm not sure but it seems to me that you also have a bias problem in the power amp. At idle the heat sink shouldn't get hot no matter how long it's been on. What do you think Steven? Bill Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5291 is a reply to message #5285] Tue, 04 January 2005 22:42   jbreher Messages: 11 Registered: January 2005 Junior Member Bill - I see your point, but how hot is hot? The measured cutout temp is 120 F - that's ambient in some parts of the country on summer days. I usually regard the possiblity of multiple independent failures as implausible. One thing we DO know is that the thermal switch is bad. I can't seem envision any case where the thermal switch problem has induced a bias problem, nor am I coming up with a plausible scenario where a bias problem could have led to this thermal swich failure. I'll get the new thermal switch in, and run the amp through its paces for several hours. If there truly is a bias problem, it'll surely rear its ugly head at that time. Either way, I'll let all y'all know how it comes out. Joe Liberty in my Lifetime! http://q-music.com http://usual-suspects.com Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5293 is a reply to message #5260] Wed, 05 January 2005 07:51   stevem Messages: 4736 Registered: June 2004 Location: NY Senior Member You may have a point Bill,120 degrees only leaves you 50% more temp rise to go before you hit the 185f cutout point!If the amp can idle and reach 120F, then it would seen to me that playing the amp at even 75% of full RMS wattage would bring you up to 185F in no time. I am going to pull my roasting thermomiter out of my babyback ribs, and over the weekend turn on one of my 250s, and my k100 and see what they temp at in idle. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5300 is a reply to message #5293] Thu, 06 January 2005 12:46 chicagobill Messages: 2005 Registered: April 2003 Senior Member Joe: I was only offering what I have seen in my personal experience to be true. I agree with you, that multiple independent component failures are rare, but they can happen. Not knowing where or how (or if) the amp was used during its past life, it would truly be impossible to state anything as definitive, but in a 30 year old piece of equipment I would guess that the two problems could have developed at completely different times. If I had to defend this position, I would think that the thermal cutoff probably fell out of spec a long time ago, but was never noticed until the overheating problem arose. Just my point of view, Bill. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5400 is a reply to message #5300] Wed, 26 January 2005 11:41   jbreher Messages: 11 Registered: January 2005 Junior Member chicagobill - Looks like your position is vindicated <sheepish grin on my face>. New thermal switch installed, amp still cutting out (though seemingly much less frequently). stevem - Did you ever get my SASE? A schematic for a similar output stage would certainly be helpful at this point. Joe Liberty in my Lifetime! Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5403 is a reply to message #5260] Wed, 26 January 2005 13:05   stevem Messages: 4736 Registered: June 2004 Location: NY Senior Member Yes, I did, I will get them out by then of the week I had to get my copys back from my brother first. Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5417 is a reply to message #5403] Thu, 03 February 2005 12:19 chicagobill Messages: 2005 Registered: April 2003 Senior Member Joe: I hope you keep us updated, as to your progress. Bill Report message to a moderator

Re: Slant face K150-1 thernal shutdown [message #5442 is a reply to message #5403] Tue, 08 February 2005 23:00   jbreher Messages: 11 Registered: January 2005 Junior Member Bill - I will keep all y'all posted on progress. Steve - got the schemes today. Thanx. I'll let you know how I make out. Report message to a moderator

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