Kustom K200A.4

[bsco]

Are the two diodes 10 volt Zeners? The K200A series of amps should have +&-40 dc supplies for the power amp and +&-24 vdc supplies for the preamps and FX switching. There should be two small pc boards on the back panel, one for each 24 volt supply.

The later K200B series amps used +&-8 vdc supplies for the preamp supply, but these were regulated supplies not Zeners. The much later Kustom 150 and 250 amps used resistors and 12 volt Zeners for the op amp supplies.

If this has been modded, what do the 10 volt supplies connect to? Are the boards all original?

If the signal dies at Q402, check to see if the circuit matches the schematic. Has there been any mods done to this board?

Thanks for the reply....I just had a quick peek as I have to run out.....There is only one board in the back....and by the looks of it, the power amp and power supply are on this board....However......there are four holes in the back panel (next to the footswitch jack), which looks as if there was supposed to be a ckt. board installed there....and on the bottom of the cabinet, it looks as if there were a couple of power transistors that were originally installed as well......but are no longer there......at present, it looks like the amp has 4 output transistors......When I get back later tonight I'll take some pics for you....by the sound of the questions you are asking, it is possible this has been hacked........many, many years ago......I shall be in touch.....

[52 Bill]

Normally there are two small pc boards mounted on the back panel near the foot switch jack. One for each 24 volt supply, each with a large power transistor.

All of the boards should have pc numbers on them. Which ones do you have there? I'm wondering is somebody swapped in some newer boards in there.

[bsco]

Normally there are two small pc boards mounted on the back panel near the foot switch jack. One for each 24 volt supply, each with a large power transistor.

All of the boards should have pc numbers on them. Which ones do you have there? I'm wondering is somebody swapped in some newer boards in there.

Hi. I'll attach a pic of the area in question...There are no boards there that you describe....just take a look.....

[52 Bill]

Well, you can see that there were transistors mounted to the chassis, but they have been removed and replaced with the power resistors and the diodes.

What is the problem with the amp? What boards do you have in there?

[bsco]

Well, you can see that there were transistors mounted to the chassis, but they have been removed and replaced with the power resistors and the diodes.

What is the problem with the amp? What boards do you have in there?

The boost and selective boost isn't working...if you crank up the main and boost volumes close to max the sound will be very distorted...I pulled associated transistors one at a time and tested them...they check ok....the boards that are associated with the boost and clipper are PC402 and PC402A...the clipper circuit works fine....

[52 Bill]

Those are the correct A series boards. You were testing voltages before you found out that there is no 24 volt power supply. How is the boost circuit powered?

[bsco]

Those are the correct A series boards. You were testing voltages before you found out that there is no 24 volt power supply. How is the boost circuit powered?

Ok. Checked that out....Those PC402 boards are powered from those Zener/resistor networks......The diodes are ECG5125A....5W 10V zeners....also, The tech that did this(He has passed away quite a few years ago), had done that....so I guess there were boards there but they were swapped out.....so, if the circuit is supposed to have 24V supplies, the clipper circuit works but I don't know if it sounds right...as it is very buzzy......the selective boost control doesn't appear to change the tone any.....according to the schematic, these circuits are supposed to have plus and minus 24V.......it currently has plus and minus 10V...so all the transistor voltages will be very low......as was mentioned earlier.......and..... as this is the first time I have seen this type of amp, I thought there might have been different versions......anyway, I was fooled......I would like to see a pic of these missing boards if there are any pics floating around......

[52 Bill]

The boards in the amp should be 2-preamps PC102, power amp PC702, Reverb/Trem/Vib PC302A&B, Boost/Clipper PC402A&B, and the two missing boards PC502 and PC602.

You could change the two Zeners and increase the voltages up to 23 volts or you could add a couple of three pin voltage regulators. I need to recharge my camera, but I will take photos of the boards for you.

[bsco]

The boards in the amp should be 2-preamps PC102, power amp PC702, Reverb/Trem/Vib PC302A&B, Boost/Clipper PC402A&B, and the two missing boards PC502 and PC602.

You could change the two Zeners and increase the voltages up to 23 volts or you could add a couple of three pin voltage regulators. I need to recharge my camera, but I will take photos of the boards for you.

Ok All the other boards are there.....I'll see if the local parts store has 24V zeners at 5W....thanks for the reply.....

[bsco]

The boards in the amp should be 2-preamps PC102, power amp PC702, Reverb/Trem/Vib PC302A&B, Boost/Clipper PC402A&B, and the two missing boards PC502 and PC602.

You could change the two Zeners and increase the voltages up to 23 volts or you could add a couple of three pin voltage regulators. I need to recharge my camera, but I will take photos of the boards for you.

I forgot about this.....I can use my lab power supply(that I recently picked up), which has current limit and has two separate adjustable 30V power supplies with a fixed 5V supply as well.....And instead of pumping 24V right off the bat, I ca probably try 15V to see if there is any improvement and I can control the current limit as well just in case there is something wrong.......then if everything still seems to be ok, I can increase the voltage until I reach the 24V mark and see where it all sits then......By all means, post the pics for the 24V supply boards......I would still like to see them......
Cheers

[olddawg]

I would be tempted to recreate the two missing boards on perf board if you can find a layout and/or a circuit diagram.

[52 Bill]

I would be tempted to recreate the two missing boards on perf board if you can find a layout and/or a circuit diagram.

The schematic is available, but probably no layout. I think that this is a customer repair, which makes that a pretty hard sell.

Here is photo of the two regulator boards.

[Jazz P Bass]

Interesting how the -23V rail is 'controlled' by the +23 V rail.

[52 Bill]

Interesting how the -23V rail is 'controlled' by the +23 V rail.

Tracking regulator.

All of the 200 series amps used this approach whether it was +&-24 volts or +&-8 volts. If both voltages were off, then you check the positive regulator. If only the negative voltage is off then check the negative regulator.

[olddawg]

A 1000uf or so cap, an isolation diode and a TIP regulator of the appropriate value for each rail should do the trick. The Zener will probably work though. Quick, cheap, and dirty! Like weekend women...