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Need schematic [message #29287]

Thu, 11 July 2024 09:10

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

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Re: Need schematic [message #29288 is a reply to message #29287]

Thu, 11 July 2024 15:22

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.

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Re: Need schematic [message #29289 is a reply to message #29288]

Thu, 11 July 2024 15:33

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.

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Re: Need schematic [message #29290 is a reply to message #29288]

Fri, 12 July 2024 09:31

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

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Re: Need schematic [message #29291 is a reply to message #29290]

Fri, 12 July 2024 10:15

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

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Re: Need schematic [message #29292 is a reply to message #29288]

Fri, 12 July 2024 12:15

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

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Re: Need schematic [message #29293 is a reply to message #29291]

Fri, 12 July 2024 12:17

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.

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Re: Need schematic [message #29298 is a reply to message #29293]

Sat, 20 July 2024 17:39

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.

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Re: Need schematic [message #29299 is a reply to message #29287]

Tue, 23 July 2024 05:11

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.

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Re: Need schematic [message #29300 is a reply to message #29299]

Tue, 23 July 2024 10:22

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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