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need help with static problem [message #20525]

Sun, 27 April 2014 16:05

vintagefan
Messages: 166
Registered: March 2014
Location: Dallas

Senior Member

Hi all......I've got some bassy pulsating static starting in my 1969 Kustom K100C-8 4-10 amp......I occurs after powering on and lasts about a minute then fades away. Occasionally the static will come back, but usually only happens right when turning the amp on. It's a bassy sounding pulsating sound as if the tremelo is on at medium speed and then it fades out. Unplugging the guitar and turning any or all the knobs on the amp have no effect on the static. While the pulsating static is ocurring I can still play and hear the guitar ok, but the static is louder than the guitar. This problem started when I played my Gibson ES135 thru the amp. The static did not start when I plugged the Gibson in, but rather when I started playing the Gibson. I sense that the humbuckers putting out a bassier sound is what caused the original static because previously I only played a tele thru the amp which puts out much less bass and the tele never caused any static. However, now static occurs when turning the amp on even with a tele. The amp is all original and I don't know if or what previous work has been done to the amp.
Trying a different cord didn't eleminate the static.

Ideas as to the problem to give a tech where to start to remedy the static?.....thanks.

[Updated on: Sun, 27 April 2014 16:06]

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Re: need help with static problem [message #20526 is a reply to message #20525]

Sun, 27 April 2014 19:52

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The reason the amp is doing that is the Gibson, just send the guitar to me and the problem will be gone. Rolling Eyes

My first guess would be that there is something loose inside the amp and playing low frequency notes has made it vibrate enough make noise.

Try this, turn off the reverb and then give the amp a good thump with your fist. Does that either cause the amp to start or stop making the noise?

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Re: need help with static problem [message #20528 is a reply to message #20526]

Sun, 27 April 2014 20:44

vintagefan
Messages: 166
Registered: March 2014
Location: Dallas

Senior Member

No, turning off the reverb and banging on the amp has no effect. I'll open it up and see if anything is loose..... thanks.

[Updated on: Sun, 27 April 2014 20:50]

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Re: need help with static problem [message #20529 is a reply to message #20528]

Sun, 27 April 2014 22:13

oren hudson
Messages: 274
Registered: March 2008
Location: Gastonia, NC

Senior Member

I'd do a good spray with Deoxit of all controls and work them real good. Dirty pots can cause this problem sometimes. Smile

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Re: need help with static problem [message #20530 is a reply to message #20525]

Mon, 28 April 2014 06:35

stevem
Messages: 4739
Registered: June 2004
Location: NY

Senior Member

My guess is that the amp has a electrolytic cap going bad in one of the circuits, maybe the tremolo, it could also be in one of the 8 volt regulator circuits, and or one of the two big main rail electrolytic filter caps mounted on the floor of the amp.
If it's a solder connection on a circuit component the most likely ones I have had that happen to are the big orange colored caps that are used in spots on all three circuit boards in the amp.
Another thing to check would be the two connections screws on top of each main rail filter and make sure that they are tight.

To get at all of this you will need to pull out the reverb pan which is done by removing the 6-32 pan head screws at each end of it's two mounting bars.
Then you need to unplug each of the RCA cables that go to the board.
Theses cables need to go back to the same jack you pulled them from or the reverb will not work.
You will not harm the amp if they get plugged in wrong, but it will not work so mark one of the cables a left or right side.
You can turn the amp on and play without the pan in the amp and if the problem is gone than you have a pan problem or a Issue in the reverb send or recovery circuit which is a good way to narrow things down.
Note that when and if you put the pan back in that the on/ off switch is very close to the pans case, so make sure you have no shorts.
Also note that the box type 5 watt resistor on the pilot lamp gets very hot and even when the amp had been off for two minutes can still burn your fingers!
The highest voltage inside the amp is the wall ac voltage, so once the amp is unplugged and the main filters drained which takes no more than a minute or two there is no risk of shock.
If all of this sounds like too much than its time to take the amp and a print off of this posting string to a tech for repair.
Good luck and kept us informed!

[Updated on: Mon, 28 April 2014 06:41]

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Re: need help with static problem [message #20533 is a reply to message #20530]

Mon, 28 April 2014 16:06

vintagefan
Messages: 166
Registered: March 2014
Location: Dallas

Senior Member

Can anyone recommend a good tech with experience recapping amps in the Plano, Texas area(Dallas)? What is your advice about what these amps need to make them last such as recapping this amp and anything else you recommend? Lastly, what 's a fair price to have this done? I plan on keeping this amp as it has the vintage bright tone I like.

I 'm in the process of cleaning and lubing the pots, cleaning plugins, & other stuff right now.

I appreciate everyone 's advice. Thanks.

[Updated on: Mon, 28 April 2014 16:18]

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Re: need help with static problem [message #20534 is a reply to message #20525]

Mon, 28 April 2014 17:15

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I don't know of anybody down in Texas, but I'm sure that one of the others here will chime in.

I personally am not a big fan of overall recapping these amps. I prefer to replace what is needed and leave the rest. But I do my own work and it is not a big expense thing for me to fix them as they need it.

I personally have never seen a set of the big Mallory caps really go bad. I'm not saying that they don't go bad, but they are often replaced for no good reason other than the fact that they are old. There are many people that feel that old caps must be replaced, but I'm just not one of them.

Steve is right, there are voltages inside the chassis that can do you harm and if you do not feel comfortable in working inside there, you should take the amp into someone that can do it safely.

I would suggest that if you have the chassis out and unplugged, go through and make sure that all of the screws are good and tight as well as the controls, etc. This includes the screw terminals on the top of the main filter caps. Don't over tighten them, just be sure that they are making good contacts.

Some circuits are grounded by mounting screws and by jack and pot nuts, so if they come loose, all sorts of odd things can happen.

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Re: need help with static problem [message #20535 is a reply to message #20534]

Tue, 29 April 2014 15:38

Kustom_Bart
Messages: 601
Registered: October 2010
Location: Greenville, MichiGUN

Senior Member

I too agree with chicagobill, Kustom amps are not the amp that you want to replace everything or do a wholesale rebuild, unless it needs it. Simply replace what is bad and play on. They do not like having everything replaced and will 99 times out of 100 give you more fits by going that route.

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Re: need help with static problem [message #20536 is a reply to message #20535]

Tue, 29 April 2014 18:50

vintagefan
Messages: 166
Registered: March 2014
Location: Dallas

Senior Member

No luck, still have pulsating bass static when powering on for a minute and then it fades away. Same static even with the reverb pan unhooked. I deoxited the pots, inputs, & some connections and everything is tight and secure. ......After the pulsating bass static fades out, the amp sounds great for hours.

If this is something like a bad cap, will it damage other components as time goes by? I'm searching for a tech with experience with these amps but I had a bad experience with a tech here ruining my Fender Custom Vibrolux Reverb tube amp and finally had to get rid of it. So I'm leary of techs here and especially techs that don't have actual experience with these transister amps.

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Re: need help with static problem [message #20537 is a reply to message #20525]

Wed, 30 April 2014 06:58

stevem
Messages: 4739
Registered: June 2004
Location: NY

Senior Member

When you turn the amp off do you get a quick pop out thru the speakers, or does the normal idle hiss just fade away?
If you have or cam borrow a voltmeter that has a Frequency test feature hook it up across the speaker output and power the amp up, what is the frequency the meter shows?

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Re: need help with static problem [message #20538 is a reply to message #20537]

Wed, 30 April 2014 09:26

vintagefan
Messages: 166
Registered: March 2014
Location: Dallas

Senior Member

Yes, there's a pop coming out of the speakers when I turn it off...and also when I turn it on.....Sorry, I don't have a volt meter.

I have 3 of these K100C-8 4-10 amps. They all pop when I turn them on or off, but this is the only one with the pulsating bass static......thanks.

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Re: need help with static problem [message #20544 is a reply to message #20538]

Wed, 30 April 2014 19:42

vintagefan
Messages: 166
Registered: March 2014
Location: Dallas

Senior Member

I will have a tech look at it next week. thanks.

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