| Fired up my Kustom Amp For First time in 20+ Years [message #26682] |
Sat, 05 May 2018 21:18  |
B-Dubs
Messages: 15
Registered: April 2018
Location: Boston, Ma
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Junior Member |
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I've fired up my Kustom Model J595RV Serial 118823 (not sure on the year, but I thought it was an early 70s model). It is a cascade model (head and cab)l, I bought it at a yard sale in the mid 80s, people practically gave it to me, so they would not have to lug back down their cellar. I believe it is a K200, after being in the closet for 20+ years. I get loud hum, no sound on main channel (channel with reverb and Vibrao), do get audio out of 2nd channel. I'm in Boston area, and will probably take to a shop, but I have done a lot of soldering in my day. Just wondering if any tips or things to look at, or worth opening up before I take it in.
Thanks,
Bob W (B-Dubs)
[Updated on: Sat, 05 May 2018 21:19] Report message to a moderator |
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| Re: Fired up my Kustom Amp For First time in 20+ Years [message #26684 is a reply to message #26682] |
Sun, 06 May 2018 14:39  |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Welcome to the place Bob.
I agree with Steve that a common failure is old electrolytic caps, but I personally would prefer to find the problems with the amp first and then replace stuff for the sake of replacing them.
Does the amp hum all of the time that it is turned on? Do the controls have any effect on the loudness or timbre of the hum? Do you have access to a volt/ohm meter?
The Frankie heads have a different power amp design that the later A and B series heads. They are great sounding amps, but they do have their quirks. If you decide to fix it yourself, we can help you here. If you send it into a shop we can also help them if they have any problems in dealing with it.
Again, welcome!
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| Re: Fired up my Kustom Amp For First time in 20+ Years [message #26688 is a reply to message #26683] |
Mon, 07 May 2018 12:46 |
B-Dubs
Messages: 15
Registered: April 2018
Location: Boston, Ma
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Junior Member |
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Thanks SteveM and ChicagoBill for the replies,
I figured bad caps. I was told it was a 70s model when I bought it, but interesting that it is 60s model. Pretty loud hum/feedback (constant), no change when dials turned. Yes, I do have a couple of multi-meters, and a solder station. I'm an IT guy and practically made a living fixing early Apple spaceship shaped Airport wifi bases, replacing 2 caps there were always bad on them. Also, I don't think the Vibrato ever worked on it, since I've owned it, the reverb did work. I tried to post a link to photo of it, but I need to post a few more times to be able too. It is in very good shape, except previous owner etched his social security number on the face of head and cab. Have the original covers, in good shape too.
Bob W (B-Dubs)
[Updated on: Mon, 07 May 2018 12:47] Report message to a moderator |
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| Re: Fired up my Kustom Amp For First time in 20+ Years [message #26690 is a reply to message #26682] |
Mon, 07 May 2018 19:04 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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The first test I would suggest is to see if there is any dc voltage on the speaker output. Use your meter set to read dc volts and test across the speaker jack or across the speaker cord 1/4 inch plug. Be careful, you do not want to short the output leads together.
There should be less than one half volt dc on the speaker jack in a normal working amp. If there is more than that, do not plug the speaker cabinet back into the head until you get the voltage problem corrected.
On a Frankie head, voltage on the output is usually a sign of a bad output transistor.
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| Re: Fired up my Kustom Amp For First time in 20+ Years [message #26691 is a reply to message #26682] |
Tue, 08 May 2018 05:53 |
stevem
Messages: 4773
Registered: June 2004
Location: NY
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Senior Member |
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Your amp has reverb, and in that model it hangs off the roof of the amp so you will need to unplug the rca cables feeding it and use a maker to note which side of the pan they get plugged back into.
No harm will come if you plug it back in wrong, but the reverb will not work well.
Also note that on the center of rear wall of the amp are the output transistor and there bias resistor network.
Even if it turns out your hum issue is not from having a bad transistor , these resistors can go way way off in value due to age , and they need to be dead on !
If they are not the amp can loose some 35 watts of its clean output power.
In light of this I would remove the one of the big tall power supply can filters to gain access to the resistors and unsolder one leg of each resistor and compare its reading to the amps schematic that can be found on this site.
And like Bill posted a D.C. Voltage found at the output jack is not good , the problem is that if you have a loud hum then that is a large D.C. Voltage ( like over 20 volts) and that can blow a speaker on you!
Please report back with your findings..
[Updated on: Tue, 08 May 2018 06:03] Report message to a moderator |
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| Re: Fired up my Kustom Amp For First time in 20+ Years [message #26693 is a reply to message #26692] |
Tue, 08 May 2018 22:22 |
B-Dubs
Messages: 15
Registered: April 2018
Location: Boston, Ma
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Junior Member |
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Hi Gang,
I opened up the amp head tonight just to have a look. I put my father-in-laws old Simpson 260 multi-meter on the output cable and I think I am getting 3 volts. I set the meter on DC+, 10v, and it is giving me 3 if I'm reading the correct scale I took a look inside, didn't see any thing obvious, like swelled popped caps, looks like a large cap has been replaced on the effects board, and it looks like there are 2 legs sticking out of same board that aren't attached to anything, but seems they should be (one has a blob of solder on end), maybe why the vibrato never worked. I took some photos, but I can't post them yet. I don't think that I am going to able to do much with it myself, but have someone that I can take to, and will pass on tips from you guys to him, and the schematics.
Thanks,
Bob W
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| Re: Fired up my Kustom Amp For First time in 20+ Years [message #26696 is a reply to message #26682] |
Wed, 09 May 2018 00:10 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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The three volts on the speaker would cause the hum that you are hearing. Your tech should check all 4 output transistors and the four biasing resistors that are connected to them, 820 ohms 1 watt and 8.2 ohms 1/2 watt.
The effects board should have a light bulb and a cds photocell to make the vibrato work. They are enclosed in a heat shrink tube. If either is missing, the vibrato will not work.
While you have the meter out, you should read the voltage across the two main filter caps. You should get plus and minus 40 volts dc or so. The last voltage test would be the preamp power supply voltage which should be around plus 25 volts dc. It is generated on the driver pc board on the rear panel. If you look at the bottom edge of the driver board, there are two or three wires that connect the driver board to the effects and preamp board. I think that the red ones will be the 25 volt lines.
The ink pen numbers on the edge of the chassis are the factory codes when the chassis was built. One fellow here figured out what they all meant and could date the chassis by reading them. He hasn't been around here recently, but if you list the serial number, somebody will be able to give you an estimate as to when it was built.
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