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Need schematic [message #29287] Thu, 11 July 2024 09:10 Go to next message
HutchAmpMan is currently offline  HutchAmpMan
Messages: 7
Registered: June 2022
Junior Member
I need a schematic for a Kustom J695 two channel amp head.  S/N is 10762

The amp had one bad power transistor (replaced with a NOS unit) but has low volume and distortion when volume is set high.  Without a schematic, I'm just reduced to guessing.

There are no markings on the PC boards as to what number they are.  The amp uses three power transistors, the first of which is connected to the preamp board with the other two paralleled from that.  The audio board is mounted on three points to the chassis bottom via 90 degree tabs.

Any help would be appreciated.

Thanks!
Tom
Re: Need schematic [message #29288 is a reply to message #29287] Thu, 11 July 2024 15:22 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4778
Registered: June 2004
Location: NY
Senior Member
Unfortunately up to this point in time  I have never had may hands on a schematic for these .
These very early amps had only two output transistors.
The other (3rd) transistor was is the driver to the phase splitter/ driver transformer.
The transformer should check out as such.

The primary should read 9.7 ohms.
On the secondary side tan to green should read about 5.9 ohms.
Brown to orange is about 6.1 ohms.

Is your audio signal into the PI transformer clean?
Is your audio  signal out of the preamp board clean?$)
All of the electrolytic type caps need to get replaced, and maybe even the main filters off of the power supply diodes.
How close the bias resistors and emitter resistors on the outputs need to test out very very close to stated values on them.

Note that these amps where all of 22 watts of clean power into 4 ohms.
Re: Need schematic [message #29289 is a reply to message #29288] Thu, 11 July 2024 15:33 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4778
Registered: June 2004
Location: NY
Senior Member
[quote title=stevem wrote on Thu, 11 July 2024 15:22]Unfortunately up to this point in time  I have never had may hands on a schematic for these .
These very early amps had only two output transistors.
The other (3rd) transistor was is the driver to the phase splitter/ driver transformer.
The transformer should check out as such.

The primary should read 9.7 ohms.
On the secondary side tan to green should read about 5.9 ohms.
Brown to orange is about 6.1 ohms.

Is your audio signal into the PI transformer clean?
Is your audio  signal out of the preamp board clean?$)
All of the electrolytic type caps need to get replaced, and maybe even the main filters off of the power supply diodes.
How close the bias resistors and emitter resistors on the outputs need to test out very very close to stated values on them.
The good thing about any early SS amps like these is the the PI transformer isolates any problems that may be taking place on either side from blowing up parts on the other side.

You can, if need be listen in on the audio drive signal coming into the primary with a pair of headphones protected by a 10 Uf 15 volt non polarized cap if you do not have a O-scope.
Note that these amps were all of 22 watts of clean power into 4 ohms.
Re: Need schematic [message #29290 is a reply to message #29288] Fri, 12 July 2024 09:31 Go to previous messageGo to next message
HutchAmpMan is currently offline  HutchAmpMan
Messages: 7
Registered: June 2022
Junior Member
I will need to find the schematic for the audio output to the transformer as my board seems go have gone dead (no power to it)

Tom
Re: Need schematic [message #29291 is a reply to message #29290] Fri, 12 July 2024 10:15 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4778
Registered: June 2004
Location: NY
Senior Member
Not likely to happen at this point, I have been looking for 30+ years.

The PI/ driver transformer  gets its power from the red wire source  that runs around the amp just like the preamp board does.

Here’s my email, please send me a bunch of good photos of the inside of this amp.

smag25ra5@yahoo.com
Re: Need schematic [message #29292 is a reply to message #29288] Fri, 12 July 2024 12:15 Go to previous messageGo to next message
HutchAmpMan is currently offline  HutchAmpMan
Messages: 7
Registered: June 2022
Junior Member
OK, just had a pacemaker put in yesterday so my coherent level may have not been good.

I do not seem to have power to the audio board (the long one where all the pots attach via wires) so I guess my question really is where does B+ come from for that board.

Thanks in advance.
Tom
Re: Need schematic [message #29293 is a reply to message #29291] Fri, 12 July 2024 12:17 Go to previous messageGo to next message
HutchAmpMan is currently offline  HutchAmpMan
Messages: 7
Registered: June 2022
Junior Member
OK, will have to go looking.  There is a red wire with a ring terminal that goes to the power lamp and from there through a resistor to ground.  Will have to hunt around but I haven't seen any signs of another red wire.
Re: Need schematic [message #29298 is a reply to message #29293] Sat, 20 July 2024 17:39 Go to previous messageGo to next message
pleat is currently offline  pleat
Messages: 1459
Registered: June 2004
Location: Belding, Mi
Senior Member
The schematic for the Kombo 1 organ has the power amp section on the schematic.
Re: Need schematic [message #29299 is a reply to message #29287] Tue, 23 July 2024 05:11 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4778
Registered: June 2004
Location: NY
Senior Member
Hi Pleat .
I should have updated what's been going on with his amp once we started to email back & forth.

At first by his statements post as to how many transistors he had on the rear of his amp I thought he had one of the first production models.

As it turns out he as a 200 model so the schematic here was was what he needed, and as it turns out his issue is int the regulation circuit.
Re: Need schematic [message #29300 is a reply to message #29299] Tue, 23 July 2024 10:22 Go to previous message
HutchAmpMan is currently offline  HutchAmpMan
Messages: 7
Registered: June 2022
Junior Member
Yes, it was.  Board has been rebuilt with NOS transistors and new capacitors and resistors that were out of tolerance.  Still working on this amp though, now focusing on the audio board.
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