Kustom K200A.4

[bsco]

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

I have thought about that......but for some reason I don't have the board layout...I do have some single sided copper clad boards....and I do have lots of pads and tape for etching......it would be alot neater to actually etch a couple of boards as the owner is in no hurry for it but I want to make sure everything is ok.....which is why I suggested using my bench supply as the substitute power source.....just to check everything out....

[bsco]

OK. Back at this one again...I had ordered in some Zener diodes....15V, 18V and 20V...I installed the 15V zeners and behold...The boost and clipper ckt worked....So. seeing as these Zeners are connected to the 23V supplies, I decided to install the 20V zeners....when I did that, The boost and clipper ckts worked but , I did notice that when the clipper ckt is maxed out, there is noise there...and this noise is there with the 15V zeners as well.... I have been told before that this circuit did not sound very good when on max....Is that true??? and when using the tremolo/vibrato function, there is a fairly noticeable hum present which is not there with the 15V zeners installed....and, I am not familiar as to how these amps are actually supposed to sound as I have never used or heard them before.....any thoughts, comments, etc welcome.....

[52 Bill]

The boost and clipper ckts worked but , I did notice that when the clipper ckt is maxed out, there is noise there...and this noise is there with the 15V zeners as well.... I have been told before that this circuit did not sound very good when on max....Is that true???

What sort of noise? The clipper is a fuzz tone. As it uses the signal from the preamp, it works best when the channel volume is turned up a little.

....and when using the tremolo/vibrato function, there is a fairly noticeable hum present which is not there with the 15V zeners installed....

Exactly what voltages are the two Zeners producing for the preamp power supplies, +&-20 volts? How much filtering is there on the two low voltage Zener supplies?

The amp originally had two 24 volt power supplies, somebody removed them and replaced them with two 10 volt supplies. Just fix the two supplies to 20 or 24 volts and move on.

The Zener supplies will need filtering on the output to help stabilize the voltages. You may need to increase the values of the caps if any are installed in there.

This is a fairly well designed guitar amp that was popular back in the day. This is the model that John Fogerty of CCR used for all of those big hit records. It shouldn't be any more noisy or any more hummy than any other amp from that time period.

First make it work and then tweak things if it's needed to make it sound better.

[bsco]

What sort of noise? The clipper is a fuzz tone. As it uses the signal from the preamp, it works best when the channel volume is turned up a little.

Exactly what voltages are the two Zeners producing for the preamp power supplies, +&-20 volts? How much filtering is there on the two low voltage Zener supplies?

The amp originally had two 24 volt power supplies, somebody removed them and replaced them with two 10 volt supplies. Just fix the two supplies to 20 or 24 volts and move on.

The Zener supplies will need filtering on the output to help stabilize the voltages. You may need to increase the values of the caps if any are installed in there.

This is a fairly well designed guitar amp that was popular back in the day. This is the model that John Fogerty of CCR used for all of those big hit records. It shouldn't be any more noisy or any more hummy than any other amp from that time period.

First make it work and then tweak things if it's needed to make it sound better.

The volume control is turned up and when the clipper ckt is engaged, and you turn it up on max, this is where you get this HF type noise...if doesn't appear to have much LF in there....if you turn the clipper level down 10 or 15% then it sounds fine.......as far as the zeners are concerned, there was no extra filtering on them...The were originally just soldered in place and grounded..so the only filtering that would be there would be the filtering on the boards themselves....I will take a peek at the schematics again to see what is on the Vib-Trem boards as this is where the hum resides when the voltage is increased past 15Volts... ......there is no noticeable artifacts when using the amp without the effects engaged...as a matter of fact, the amp is louder...I shall get back to you shortly....
Thanks for the reply.....

[R.G.]

Let me insert my common comment. Others here will be bored to death with it by now, but it's valid.

When you're resurrecting something like this, replace all the electrolytic caps before you start trying to debug.

The K200s were a late-60s kind of thing, so the caps in it are over 40 years old. Electros may last a long time if they're well taken care of, powered up every week or so, not exposed to heat, and you 're just plain lucky. They eventually rot into uselessness no matter what you do.

Electros often bypass biasing elements, and this can throw off the bias point of circuits that otherwise work just fine. IMHO, it's a good investment of your time to replace them all before any significant troubleshooting and tracing, and a waste of time if you find a bad cap, get it "fixed" and then have another cap fail in a week.

[bsco]

Let me insert my common comment. Others here will be bored to death with it by now, but it's valid.

When you're resurrecting something like this, replace all the electrolytic caps before you start trying to debug.

The K200s were a late-60s kind of thing, so the caps in it are over 40 years old. Electros may last a long time if they're well taken care of, powered up every week or so, not exposed to heat, and you 're just plain lucky. They eventually rot into uselessness no matter what you do.

Electros often bypass biasing elements, and this can throw off the bias point of circuits that otherwise work just fine. IMHO, it's a good investment of your time to replace them all before any significant troubleshooting and tracing, and a waste of time if you find a bad cap, get it "fixed" and then have another cap fail in a week.

Thank you R.G. this amp was in storage for quite a few years....and I noticed that the majority of caps in here are orange disc shaped caps which are polarized.....the clipper ckt works fine unless of course you max out the clipper controls...turn them down a bit and you have a pretty good sounding distortion....and the owner had told me that it was always that way ever since he owned it....the trem/vib function works great at 15V but when trying to increase that voltage up to 20V, then this function produces a hum just with the function turned on....and this hum will be "In Time" with whatever way the speed and intensity controls are set...keep the voltage at 15 and it sounds great....if filter caps in this circuitry were the problem, then wouldn't it also produce this hum at 15V as well??? The owner gave me another set of schematics.....now I have two sets...one with plus and minus 8V supplies and the other with 23V supplies....I am going to have to go through these to see exactly which ones apply to this unit....this could be part of my problem........if any thing else comes to mind, fire away.....
Cheers.
P.S. That transformer tester you had posted on line works out great...I have used it a few times since I had found it with great results.....Thank you very much....

[R.G.]

I noticed that the majority of caps in here are orange disc shaped caps which are polarized.

?? I don't know of any electrolytic caps that are disc shaped. The only common disc shaped caps are ceramic, and those are not polarized. That confuses me. All the polarized caps I know of are either cylindrical if aluminum electros, or rounded-blob for epoxy-dipped tantalum.

the trem/vib function works great at 15V but when trying to increase that voltage up to 20V, then this function produces a hum just with the function turned on....and this hum will be "In Time" with whatever way the speed and intensity controls are set...keep the voltage at 15 and it sounds great....if filter caps in this circuitry were the problem, then wouldn't it also produce this hum at 15V as well???

Electros are used as much more than filter caps. In most if not all solid state stuff, they're used for signal coupling, emitter bypassing and sometimes helping with feedback networks. It is possible that electros are behind the issues with trem here. Or not. But there's no good way to tell until you eliminate the possibility, and replacing them all is the same amount of work or less than isolating whether it's an electrolytic cap causing the problem.

When you check schemos against the actual circuit you have, let us know which schemo applies and I can help with sorting out which cap is electro and which isn't.

The owner gave me another set of schematics.....now I have two sets...one with plus and minus 8V supplies and the other with 23V supplies....I am going to have to go through these to see exactly which ones apply to this unit....this could be part of my problem.

Yep. That will be very important!

P.S. That transformer tester you had posted on line works out great...I have used it a few times since I had found it with great results.....Thank you very much....

You're very welcome. Glad I could help.

[bsco]

?? I don't know of any electrolytic caps that are disc shaped. The only common disc shaped caps are ceramic, and those are not polarized. That confuses me. All the polarized caps I know of are either cylindrical if aluminum electros, or rounded-blob for epoxy-dipped tantalum.


Electros are used as much more than filter caps. In most if not all solid state stuff, they're used for signal coupling, emitter bypassing and sometimes helping with feedback networks. It is possible that electros are behind the issues with trem here. Or not. But there's no good way to tell until you eliminate the possibility, and replacing them all is the same amount of work or less than isolating whether it's an electrolytic cap causing the problem.

When you check schemos against the actual circuit you have, let us know which schemo applies and I can help with sorting out which cap is electro and which isn't.


Yep. That will be very important!

You're very welcome. Glad I could help.

Ok R.G. The schematics for the piggy back boards for the reverb and tremolo/vib function are P302A and P302B...and it shows the B+ line as 23V....I am going to take a couple of pics and post when I get back in...Have to run an errand.......will be in touch...
Cheers

[52 Bill]

Ok R.G. The schematics for the piggy back boards for the reverb and tremolo/vib function are P302A and P302B...and it shows the B+ line as 23V....I am going to take a couple of pics and post when I get back in...Have to run an errand.......will be in touch...
Cheers

This will be my last post on this thread.

We already proved by the board numbers that this is a K200A-4 amp. The power supplies for the preamps and for the switching are supposed to be plus and minus 23 volts dc.

We also know that the previous tech had removed the two low voltage regulator boards and replaced them with a power resistor and Zener diode to set the voltages at 10 volts. Maybe he thought that because the newer version K200B amps used + and - 8 volt supplies that this one should too. I don't know why some people do the things that they do.

The orange disc caps are actually tantalum caps. Kustom used a lot of tantalums in all of their amps, some were orange, some black. I'm certain that they all need to be replaced, but for now fix the real problems and then upgrade.

[bsco]

This will be my last post on this thread.

We already proved by the board numbers that this is a K200A-4 amp. The power supplies for the preamps and for the switching are supposed to be plus and minus 23 volts dc.

We also know that the previous tech had removed the two low voltage regulator boards and replaced them with a power resistor and Zener diode to set the voltages at 10 volts. Maybe he thought that because the newer version K200B amps used + and - 8 volt supplies that this one should too. I don't know why some people do the things that they do.

The orange disc caps are actually tantalum caps. Kustom used a lot of tantalums in all of their amps, some were orange, some black. I'm certain that they all need to be replaced, but for now fix the real problems and then upgrade.

OK there BILL.......I get your point.... I just wasn't sure and wanted to check.....yes they are tantalum..... they are usually yellow in color....at least all the ones I have seen in the past....have a good Christmas.....

[Enzo]

A lot of tants are yellow, but they also can be orange or blue or puke green or brown... I don't think of color, I ID them by their shape. The ones I have seen over the years tended to be little round blobs, tear-shaped.

[bsco]

A lot of tants are yellow, but they also can be orange or blue or puke green or brown... I don't think of color, I ID them by their shape. The ones I have seen over the years tended to be little round blobs, tear-shaped.

Thanks Enzo....These threw me off because they were extremely large for a 35V cap....they reminded me of the 1600V ceramic discs you would find in TV ckts only bigger......and of course a different color.....Merry Christmas....
Cheers

[Downpour04]

Anybody here have any experience with this head?? It is original....of course it needs a good cleanup.....pots and jacks...etc...tremolo and reverb work...but there is a Selective Boost circuit and a clipper circuit.....I guess the boost selection will increase overdrive which then can be controlled by the Boost volume........this does not do anything so I have a problem there......but what about this clipper circuit......what exactly is it's function? Is it used to manipulate high freq content in some way?? any info greatly appreciated......
Cheers,
Bernie

Do you happen to still have this amp?

[bsco]

Do you happen to still have this amp?

No. That was years ago..and I have never seen a Kustom amp since....

[bsco]

Do you happen to still have this amp?

Did some checking in my stash of schematics...I can't find them at the moment as I shut my repair business down back in Aug....I have everything stored in boxes and haven't got everything unpacked and sorted out...the clipper ckt is a fuzz ckt...if you remove the front panel boards for servicing, you must ground them to the chassis as the chassis is the ground for the boards when they are bolted into place...I used a jumper wire to clip a pot body to the chassis for ground while working on the boards....I have only seen one of these and the one I had for repair needed a good cleanup and recap...hope this helps you out...
Cheers