Home » VintageKustom.com » Repairing Kustom Amps » K 100 8 (Some General Questions)
K 100 8 [message #26991] Sat, 22 September 2018 04:29 Go to next message
FeltonPruett is currently offline  FeltonPruett
Messages: 5
Registered: September 2018
Junior Member
I came across a '69 K100 8 on Craigslist. YA! My first amp in junior high. It works OK for it's age, the only thing I've found so far is a volume drop when the Trem-Vib (which works) is turned on and when the intensity is turned to 5 o'clock there's more treble. The other thing is when the normal channel is dimed it distorts horribly. A wretched, garbled robot death noise from hell. I'm planning on changing out a lot of capacitors and I've done cap jobs on tube amps... why so many electrolytic caps? I've never seen anything like it. At least it looks fairly easy to work on. Any tips, suggestions or advice on this amp much appreciated.
Re: K 100 8 [message #26992 is a reply to message #26991] Sat, 22 September 2018 06:23 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
Hello and welcome!
Yes, a bunch more secondary power supply caps and uncoupling caps in a SS amp as compared to a tube !

I would make a list and replace all the electrolytics that are on the 1400 and the 1500 preamp boards since your in there anyway as your taking well less then 20 bucks worth of parts even if you go with top shelf parts!

While you are working on the normal channel I would also replace the first 2 transistors off of the input jack, as one of these could be your issue and if nothing else new current type transistors have a lower noise floor!

Note that on these amps one input jack is briter sounding then the other, not lower gain like the number 2 input as on tube type Fenders and others!

Also note that the 2N5033 transistors on the 1500 board are FET type transistors, not the common bipolar tyoe.

These two boards run off of a positive and negative 8 volt power supply rail that is regulated .
The negative 8 volt rail tracks off of the positive, so if both rails are reading over 8.750 volts there is a issue.

Be very carful with the metal case diode that is held in the clip on the heat sink between the two output transistors as its leads are prone to breaking off at the body if they get moved around too much.

Keep us informed on how it goes.

[Updated on: Sat, 22 September 2018 06:31]

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Re: K 100 8 [message #26993 is a reply to message #26991] Sat, 22 September 2018 12:54 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Welcome!

There are more electrolytic caps in a solid state amp, because the circuit impedances are lower and all of the coupling caps have to have higher values than those in a tube amp. Typical tube amp coupling cap is less than 0.1uF, which would never be an electrolytic.

Again, welcome!
Re: K 100 8 [message #27000 is a reply to message #26993] Mon, 24 September 2018 01:53 Go to previous messageGo to next message
FeltonPruett is currently offline  FeltonPruett
Messages: 5
Registered: September 2018
Junior Member
Great info, thanks. Starting in on the parts list now. I'll let you know how it goes.
icon5.gif  Re: K 100 8 [message #27013 is a reply to message #27000] Sat, 29 September 2018 04:28 Go to previous messageGo to next message
FeltonPruett is currently offline  FeltonPruett
Messages: 5
Registered: September 2018
Junior Member
Man, I'm already stuck. The caps on this thing have me confused. Really low value electrolytic caps like 33-15, 33pF 15 V am I reading that right? What happens if I put a regular ceramic non polarized in there? Common sense tells me not to do that, what's up with this thing?
Re: K 100 8 [message #27014 is a reply to message #26991] Sat, 29 September 2018 06:10 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
The caps you should be concerned with on that board , or any circuit board in the amp are shown in the schematic on this site as having a + and - at each end of it because they are polarized, and these caps are rated in uf, not pf.
These days we have new electrolytics you can buy that are non polarized which will make your repair work easier .
Re: K 100 8 [message #27016 is a reply to message #26991] Sun, 30 September 2018 21:14 Go to previous messageGo to next message
FeltonPruett is currently offline  FeltonPruett
Messages: 5
Registered: September 2018
Junior Member
OK. So the caps I'm looking at on the boards that say 10, 33, 1 are uF. I can't find some of the lower values like for instance .033 uF in an electrolytic but I'm seeing articles that say MLCC's can replace electrolytic caps. Does anyone have experience with that? Thanks.
Re: K 100 8 [message #27017 is a reply to message #26991] Mon, 01 October 2018 07:33 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
These are the main caps I would be concerned with at first on PC1500
C1501, 100uf/ 25 V
C1503, 33uf/ 25V
C1506 100uf/25v
C1507 33uf/25v
C1510 1.0uf 25v
C1531 33uf/25v
C1532 100uf/25v
C1533 10uf/25v
C1542 10uf/35v
C1522 10uf/25v
Re: K 100 8 [message #27018 is a reply to message #27017] Wed, 03 October 2018 01:38 Go to previous messageGo to next message
FeltonPruett is currently offline  FeltonPruett
Messages: 5
Registered: September 2018
Junior Member
I'm a newbie at transistor amps, they seem a little more complicated to work on than I thought. Great place to start, thanks!
Re: K 100 8 [message #27019 is a reply to message #26991] Thu, 04 October 2018 06:09 Go to previous message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
The early kustom amps before the B series atleast in terms of the preamp sections are much more tube like with there single rail ( positive and ground ) power supplies.
Early solid state Sunn , Accostic and many many others where the same way , even including the output stage in many of them!
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