kustom amp

[billcreller]

 I'm looking for a schematic for a Kustom K100B5 amp.  My son uses one for a PA, and it has developed a hum.  Not being into SS stuff, it may be a power supply filtering issue (??)  Of course if I get into it a bit I may figure out where the PS filters are, and what they are. This thing has to be from the late 60s to early 70s.  I bought it new but don't remember when.
BILL

[6G6]

P/S filters are still the same on SS stuff as they are on tube stuff, just lower voltage.
If it is that old, I'd say they are due for replacement, wheather that fixes your hum or not.
I never worked on an old Kustom, but I do remember seeing in one and there's not a lot there
 to figure out.

[tubesornothing]

I would solve hum just like a tube amp.

Like you figure it is likely the filter caps, but there are a few things you can do before going down that road.

Is there any particular things that changes the hum?  Unplug guitar cable? Rotate pots any change?

Is it 60Hz or 120Hz (A# on 6th string).  Most likely 120Hz if it didn't have the problem before and was a production amp.  A scope will help a lot here if you can get your hands on one, as its difficult to pull transistors (unlike tubes).

Try chopsticking too, it might be a loose connection.

[GroundhogKen]

Just like Tubesornothing said---look for problems like input jacks with open shorting contacts.  Look for broken solder joints.

If you have a spare 47uF cap for a tube amp, you can wire it in with alligators to the main DC supply and see if it quiets the hum.  If it doesn't, the filter caps are not the primary source of the new hum.  (You may need two caps if it runs bi-polar)

My brother has a Kustom 200b.  I put a grounded cord into it.  It didn't look like it would be fun to work on beyond that.  Sounds great though--plug in and you've got instant Creedence Clearwater Revival.


Ken

[PRR]

> 47uF cap for a tube amp, you can wire it in with alligators to the main DC supply and see if it quiets the hum.

Transistor amps often run 1,000-4,700uFd main caps. Even if dead, 47uFd isn't going to make a big difference.

Try a DVM on AC range with a 0.1uFd cap in series with the red lead. Put black to ground, touch red to each "live" point on the main filter cap(s). At idle it should read 1V AC or less (after the thump of connection). If it shows 30V AC, the filter cap is quite useless.

[bnwitt]

Bill,
try getting ahold of Kustom:

http://www.kustom.com/Default.aspx

[billcreller]

Thanks for all the responses guys.  I will get into it and see if I really want to fool with it.

[jjackson7]

I have one of these that a friend gave me. The bridge was shorted and the first filter cap is shorted. Anyone know where to find these 2500ufd 50v mallory screw terminal caps? Also, if anyone has found a schem please share. Thanks, Jordan.

[PRR]

> screw terminal caps?

Lose them. Supposed to be "Computer Grade", but they failed a LOT.

Modern snap-in caps are built much better.

[jjackson7]

Oh my mistake the caps are fine. It was the transistor collector grounding to the heat sink. Got it going. Now if I just had a practical use for this thing. Probably headed to CL.