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Repairing A Kustom 100 4 CH PA head [message #28027]

Mon, 15 February 2021 02:07

Cody UNO
Messages: 35
Registered: February 2021

Member

Hello.
Hope everyone is staying warm. Not only is Mardi Gras cancelled, but we are expecting a big winter storm here in New Orleans.

Before I tell you about my amp issues, I just want to say that I am very thankful for this site and the info I have gotten. I just started collecting these amps and don't know much about them so all your knowledge and help is greatly appreciated.

So, on to my amp situation...

I drove 14 hours total yesterday ($75 was hard to turn down) for a cool little gold K100-5 Kustom 4-channel head. Serial #35817. I tested it tonight and noticed a few odd things. I think a few of the issues may have been addressed in a previous thread about a 200 version so I wont mention them.

1. The bass control on Channel One works until it goes over about 90% then it kinda cuts out. Im thinking some Deoxit might solve this issue. *Update: Contact cleaner fixed this*

2. You can hear the reverb tank make that typical sound (?) whenever the amp is first turned on as well as anytime I unplug from one channel and plug into another.

3. The reverb doesn't actually work on any of the channels. If I turn up the reverb knob, it lowers the volume a little bit on that channel. I opened the amp and everything is still plugged in (RCAs).

4. Channel Four has less volume than the other three. When I set all four amps to the same settings (as close I can) then Channel Four requires more volume. To give you an idea, if Channel 1-3 is at 9 oclock then Channel Four would need to be around 11-12 oclock for the same volume.

5. The power light occasionally dims for a moment. I have the amp plugged into a Furman Power Conditioner. Hoping the K100 may just need a new bulb.

6. This isnt an issue, but a question. What are the outputs on the back? Mine isnt labeled like my K250. Im assuming two speaker out, a RCA out, and a module out?

[Updated on: Mon, 15 February 2021 04:10]

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Re: Repairing A Kustom 100 4 CH PA head [message #28029 is a reply to message #28027]

Tue, 16 February 2021 07:31

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Hi!

Your trouble with the Bass pot as you have assumed is due to needing to be flushed out well with something like CRC brand electromotive cleaner and then lubed up with Deoxit brand F5.

Your reverb problem is due to two things or 3 things.
1) one of your reverb pan cables are bad. This can be checked with a ohm meter / continuity test out.
2) A wire has broken off of the RCA jack ohm the inside of the pan.
3) A wire has broken off of the coil bobbin inside the pan. This condition would require ordering up a new tank.

The volume difference on ch 4 could be due to the pot itself since they have a 10 to 20 percent resistance tolerance, or the first gain stage Transistors on that preamp board needs to be replaced, or has been replaced already with one who's gain factor is lower.

The pilot lamp dimming on this and many other Kustom amps is normal since it's powered off of the D.C. Voltage side of the power supply.
The louder the amp is played the more the pilot lamp will dim.

The rear of the amp has the two speaker outs wired up in parallel .
The amp is made for a 8 ohm load so the two original PA speakers where 16 ohms each.
The RCA jack is a recording output , but could be used to drive another unbalanced power amp
Max signal output on this jack is 3 volts.

[Updated on: Tue, 16 February 2021 07:33]

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Re: Repairing A Kustom 100 4 CH PA head [message #28030 is a reply to message #28027]

Tue, 16 February 2021 13:10

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Steve forgot to mention that the last 1/4" jack on the back is for the reverb footswitch.

There could also be another reason for the dead reverb. The drive circuit of the amp may be faulty. The cable, connection, broken tank wires are the most common reasons for no drive problems.

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Re: Repairing A Kustom 100 4 CH PA head [message #28032 is a reply to message #28027]

Tue, 16 February 2021 18:02

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Thanks for catching me on that Bill!
Gez! You'd think that since a band I was playing in the early 70s and the fact that we had a K200B-5 that I would remember the foot switch jack, lol!

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Re: Repairing A Kustom 100 4 CH PA head [message #28033 is a reply to message #28027]

Wed, 17 February 2021 06:40

Cody UNO
Messages: 35
Registered: February 2021

Member

Thank you guys so much for the replies and help. I can't tell you how much I appreciate it.

I have several voltmeters here at the house. I've used them to test the output on guitar pickups before. Is there a certain way I can test to see if that is the issue on this Reverb tank?

If the tank itself is in fact bad is there a particular brand or model that you would recommend? Mine is mounted to the top of the chassis.

I sprayed deoxit on the bass pot and it cleared it up right away.

The Channel with less volume actually sounds good even though I have to turn it up more. I'm going to eventually get my friend who is going to convert the power cable to a 3-prong to look at it so I'll mention that transistor to him.

My cascade K300 six channel head was supposed to arrive yesterday, but the UPS driver said it wasn't on his truck for some reason. They guaranteed me delivery today so I'm hoping everything works like it should on that one. I got it from a Guitar Center in Syracuse, New York and the manager claims to have tested it thoroughly. But we are talking about GC here haha.

Now, I just need to buy some more Kustom cabs. Smile

Thank you again for sharing your knowledge. This site is absolutely amazing. I wish my Dad was still alive so I could tell him about it. He was the one who got me into all of these amplifiers.

[Updated on: Wed, 17 February 2021 06:41]

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