| Installing 3 wire cord in K250-1 [message #18503] |
Sun, 24 March 2013 21:01  |
braud357
Messages: 154
Registered: July 2010
Location: Louisiana
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Senior Member |
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I am going to post pics tomorrow of my latest snag - a K250-1 head PLUS a 2x12 + 2x10 cabinet in black. I have done the 3 wire, grounded cord change on a K200 before, but never on a K250. I see that the "death cap" is mounted on the polarity switch. Do I simply remove it from the switch, then ground to the chassis ?? Thanks in advance !!
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| Re: Installing 3 wire cord in K250-1 [message #18505 is a reply to message #18503] |
Mon, 25 March 2013 12:53  |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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If you clip the cap lead from the switch and remove the ground cap, that will take the polarity switch out of circuit.
Ground the green lead from the new power cord directly to the chassis.
And be careful working on the switch wiring. The switches have a tendency to break fairly easily and are impossible to replace.
[Updated on: Mon, 25 March 2013 12:57] Report message to a moderator |
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| Re: Installing 3 wire cord in K250-1 [message #18525 is a reply to message #18503] |
Tue, 26 March 2013 15:05 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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What you did should have worked. Check the wiring on the back of the polarity switch for shorted connections. Those switches are somewhat fragile and will break apart if they are handled roughly. And double check the connections that you made by adding in the new cord.
The polarity switch has both sides of the ac line connected to it. The switch connects the ground cap to one side or the other. If you remove the cap, then the switch has nothing to connect to the ac line, so leaving the wiring should not be a problem. Unless of course the wires get shorted together.
And yes, the fuse may have blown. Did the amp work when you got it? The original fuse is soldered in, you can either solder in a replacement or add a small fuse holder so that new fuses can just be popped in or out. The fuse rating is 3 amp slow blow.
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| Re: Installing 3 wire cord in K250-1 [message #18529 is a reply to message #18503] |
Wed, 27 March 2013 02:13 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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All of the ac wires that go to the polarity switch can be removed leaving the switch there to act as a pilot lamp if you want.
The switches usually break off from the threaded mounting section. If that is what happened to yours, you can try and take a couple of cable ties and use them to hold the switch body in position.
There are any number of switches that can be mounted in the front panel hole. Finding a lighted blue push switch is posible, but will probably cost around $30 dollars. I usually can get the broken switches to work with the cable tie trick. Worst case I will get one of the two switches to work and will use the working one for the power and use the dead one to fill the polarity switch hole.
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| Re: Installing 3 wire cord in K250-1 [message #18530 is a reply to message #18529] |
Wed, 27 March 2013 06:05 |
braud357
Messages: 154
Registered: July 2010
Location: Louisiana
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Senior Member |
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My polarity switch has broken off one of the connection terminals - where the black wire connects. If using another switch - where would I connect this black wire. Sorry for the newby questions, but I cannot figure out where ! I would like to install a toggle switch for power on the back, and leave the Licon switches for pilot lights. Could you tell me how to wire a toggle ??
[Updated on: Wed, 27 March 2013 06:11] Report message to a moderator |
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| Re: Installing 3 wire cord in K250-1 [message #18546 is a reply to message #18503] |
Thu, 28 March 2013 13:15 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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I would suggest that for this and any other future project, that you build yourself a light bulb limiter or fuse saver. This is nothing more than 60-100 watt light bulb wired in series with an ac outlet and power cord. If you search the web, you will find at least 3 or 4 sites that give complete construction details.
When an amp with a power short is plugged into the limiter the bulb will light up, taking all of the current that the amp is drawing, thereby saving the fuse from blowing and also saving the good parts of the amp from additional stress from being powered on with the short.
Te begin with, make certain that the ac wiring that you have been working on is correct and no longer an issue. You can't test anything if the ac wiring is not working correctly. You can remove the wiring from the original switches and rewire the amp with a new power switch and fuse. If you need help, I can pull open my 250 head and tell you what needs to be changed. Whatever you do, just be careful when working on the ac stuff.
As a starting reference, the main reason for blown fuses in all Kustom amps is shorted output and or driver transistors. To test yours, pull the black plastic connector off of one of the power transistors that is mounted on the bottom of the chassis. There are three terminals to these transistors, the Base, the Collector and the Emitter. The pin that the blue wire connects to is the Base, the pin that the yellow wire connects to is the Emitter and the case of the transistor which has the red wire connected to it is the Collector.
With the amp off and unplugged, take your ohm meter or multimeter set to diode test and touch one lead to the red wire on the transistor case. Now touch the second meter lead to the Emitter pin (yellow wire) and see if you get a meter reading. Now reverse the two meter leads and see if you get a reading. On these transistors you should get a no reading or infinite ohms reading across these two terminals.
Now take your red meter lead and touch it to the Base pin and take the black lead and touch it first to the Emitter pin and then to the Collector terminal. Note the readings you get if any. Now reverse the meter leads and touch the black lead to the base and the red lead to the C and E terminals. Note these readings.
You should get a low reading with the leads connected one way and no reading with the leads reversed. Now repeat this test on all the output transistors.
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| Re: Installing 3 wire cord in K250-1 [message #18552 is a reply to message #18551] |
Thu, 28 March 2013 19:47 |
braud357
Messages: 154
Registered: July 2010
Location: Louisiana
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Senior Member |
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To chichagobill, stevem, and pleat - I appreciate you putting up with a neophyte. I really appreciate all of the help and advice you have given me. I thought about this problem all day at work, and began to wonder if the new cord I installed was bad. So, when I got home I quick-wired in another cord, plugged it in. I have the on-off switch bypassed, and it immediately tripped the receptacles circuit breaker. So, this could mean a dead short ! I have been wondering where to hook the black wire that ran from the fuse to the polarity switch. Looking at the schematic (with my limited electrical background) I had figured that it hooked to ground. By doing this, I had the neutral AND the green wire grounded to the chassis. Thinking this could not be right, I decided to try one more thing. I got the original, 2 wire power cord and hooked it back up ----- THE AMP WORKS !!!!!! Alleluia !
Both of the Licon switches were bad, come to find out, and I had a wire hooked up wrong. I am going to install a toggle "on-off" switch and a fuse holder on the back panel, and try to figure out how to get a pilot light bulb to work. I still cannot figure out where I should hook the black neutral wire and the new cord's green ground wire. Hell, I can live with a 2 wire cord if need be - I am SO glad that I did not fry the amp with my electrical "skills" !!!
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| Re: Installing 3 wire cord in K250-1 [message #18555 is a reply to message #18503] |
Thu, 28 March 2013 23:05 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Here is the correct way to wire the new switch and fuse. The white wire from the power cord is the neutral line. It should connect directly to one side of the transformer primary.
The green wire from the power cord is the ground and should be connected directly to the chassis.
The black wire of the power cord is the hot line and should first go to the fuse holder. The second side of the fuse holder should go to the thermal switch that is mounted to the heatsink. The second side of the thermal switch should go to the new power switch. The second side of the power switch should go to the second side of the power transformer primary.
The original Licon switches have pilot lights inside them that are powered by the amp's power supply. If you want to leave them in place, you can do that and keep the pilot lamp wires as is.
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| Re: Installing 3 wire cord in K250-1 [message #18559 is a reply to message #18503] |
Fri, 29 March 2013 09:50 |
C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...
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Senior Member |
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I have been watching this for quite some time. I think I caught something that needs clarification. The green wire is the equipment ground. It goes directly to the chassis. It's function is to be a path that protects the user from electrical shock by becoming a conductor for any fault voltages within the equipment. The white wire is the grounded conductor. In all power services (your panel in the basement)the white wire goes to a neutral bar that is bonded to ground. The black wire is power. All that being said, if for any reason, the black wire somehow got connected to the chassis, either intentional or not, that would have been a dead short and some protection device would have tripped. If the fuse is first thing in line, that would have blown immediately. If you removed the fuse and went directly to the amp, the house circuit breaker would have tripped. Just make sure that the only wire that goes to the chassis is the green wire. The white and black end up going to the transformer through the fuse and power switch. The ground switch either picks up the black or white wire and takes it to the chassis through the death cap. I just had a thought, when you removed the death cap, did you replace it with a piece of wire? That would explain the dead short that blew the fuse. The death cap needs to be removed and that is all that needs to be done. Sorry for being so long winded.
Conrad
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| Re: Installing 3 wire cord in K250-1 [message #18563 is a reply to message #18503] |
Fri, 29 March 2013 13:19 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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The only thing missing from your description is the power switch which should be added between the fuse and the second side of the power transformer primary winding.
One point of reference here is the use of the word ground. Ground or earth is not technically the same as the neutral line and should not be called a ground. Even though as Conrad pointed out they are normally connected together at the breaker box, when wiring anything, the two wires must be thought of as separate conductors.
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| Re: Installing 3 wire cord in K250-1 [message #18565 is a reply to message #18563] |
Fri, 29 March 2013 14:05 |
C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...
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Senior Member |
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I should have added that the White wire is the "grounded" conductor. This means that it does conduct current, the same current that comes from the black wire. (The AC part will be left alone) The green or green/yellow wire is the equipment ground, it does NOT conduct any current unless there is a problem.
Conrad
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| Re: Installing 3 wire cord in K250-1 [message #18574 is a reply to message #18565] |
Fri, 29 March 2013 23:07 |
braud357
Messages: 154
Registered: July 2010
Location: Louisiana
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Senior Member |
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I have fully functional K250-1 head !! Thanks to all of you for your knowledge and advice. I had to make a few changes - I installed a inline fuse holder, and found a different solution for both the on-off switch and the pilot light. I went to my local Radio Shack store to buy a toggle switch. While looking through the switches, I saw a SPST Illuminated rocker switch. It had a square flange, and looked to be almost the same size as the outline on the faceplate. It was rated 10A at 125VAC, and I figured for $5.00 I would take a chance. After minor rounding of the square hole, I had it bolted in. I put it all together and was greeted with a firm "thump" from the speakers, I plugged the polarity switch hole with one of the bad Licons, and I am now in business !! Tried it with the first bass in the rack - a Peavey Axcelerator Plus. It runs pretty quiet for a 40+ y/o amp, and sounds pretty good as well. I will try to post a pic of the installed switch tomorrow. The Radio Shack part number is 275-0692 if you want to look it up on their website. I only wish that it was a purple light, instead of red !
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