I just purchased a used KB-100 Keyboard Amplification System.
3 Channel Input, with pull Gain
Master Reverb
4 Channel EQ

Detailed info:
Seriel #: 7A-02815100
Model: KB-100
Number in bottom right of tag is 87A

I played it for a bit to test it, and it sounded excellent. At this time it was extremely dusty, so I pulled the speaker, spring reverb and amp out so I could blow it out with compressed air.

I then proceded to wipe down the exterior (cabinet only) with an armorall dampened rag to shine it up.

When I put the system back together and started to play it, the speakers now crackle badly, as if they were blown..... (This happens when run through any channel, so this problem has to be common to the 3 channels.) To make sure I hadnt damaged the speakers, I connected them to another amp (same ohmage and wattage) and they test out fine...

Next I connected the amp itself to another set of speakers and the other set of speakers makes the same rattling sound so I know for sure it is indeed something to do with the amp. Again, it must be common for all 3 channels, as it happens with all of them.

I also noticed that when nothing is plugged in, and the 4 channels on the EQ are maxed (this is while I was testing it) that the compressor comes on and (inside the cabinet, center of the heat dissipator) the compressor makes a very high pitched whine (I have really good ears, my wife cant hear it).

Is there possibly some way to bypass the compressor to see if it is what is causing the problem?

Any Ideas as to the solution to this problem (Please dont tell me to purchase a new amp, as I just got this one and would like it fixed, as its just the right size.) would be appreciated.

Thanks,
Arrick.

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Thanks for the post, however after having completed those tasks (cleaning) and no change, what's next?

This also happens with the spring reverb disconnected all the way....

Isolate the problem.

Plug your signal into the power amp in jack on the amp. How does that sound? SOund OK? Then the power amp is OK. Still bad? Probe a plug in and out of the headphones jack a few times. Does the probing seem to affect things? I mean other than cutting out the speaker each time.

How does it sound through headphones, for that matter.

Run a cord from preamp out jack to the input of some other amp and speaker. This way we listen to the preamp's sound. OK or bad? If OK the problem lies after that point If bad still, the preamp has the problem.

SInce the preamp out and power amp in are the same point in the circuit, try this: Plug a spare cord from preamp out to power amp in jacks. Any help?

Is there an "Insert" jack on the panel? Probe that jack a few times. ANything?

Plug a cord into the insert and run it to another amp. This comes from the point where the three channels JUST meet and join. DO they sound OK? Bad?

And plug your signal into the insert jack, but stop halfway in at the firwst light click. SHould have sound out the speaker - how's it sound?


Once we determine where in the amp the problem lies, we can narrow down the cause. I'd be looking for things knocked loose in the cleaning process. Like cracked solder on the larger filter caps, or the rectangular cement resistors.

Ok, I have singled it down to two possible critters....

does anyone have a schematic for this amp, so I can get the correct part numbers (they are too muddlesd to read).

I believe the built in compressor is the problem, or at least the two items on the (I believe this is it) heat board in the amp.

There is the item in center with the 2 yellow wires, but I believe the other two items (on the ends) are the problems.

Ummm........


Peavey has all the schematics you need, contact customer service and request them.

How have you determined this fault? The compressor functions are not on the heatsink .

The items on the ends of the heat sink rattle rather loudly if you turn the amp unit upside down, and they both tend to get *really* hot.

The compressor also stays lit when mid and mid-high are both above 7 with nothing plugged in (seems to be something wrong with that picture to me), however when I use canned air to blow on the two items on the ends of the heat sink, the compressor light goes off, and the unit seems to play fine. (only until it heats up again.)

I am having serious trouble with loose things on the heat sink getting hot. How about posting a photo?

Attached is a copy of the visual of the board, I dont have a digital camera at the moment, my son dropped it in the lake last summer.

The parts that are circled are the ones that get really hot (hot enough to cause the shell to melt a table cloth under the amp when sitting upside down on the kitchen table).

These items are not loose on the heat sink, however, they do make a rattling noise. It is unknown to me at this time what those two items are.
Part: Q9 and Q6,
Item Number: 6392 (they are identicle, except the Q9 and Q6 identifiers)

Thanks for all the replies.

OK, those are your output power transistors. If they get real hot, somehting is very wrong. They should not be loose in any way. When you turn the amp over you say they rattle? Are you sure you are not hearing the chassis mounting nuts moving in their little mounts?

Those transistors are type 6392 - that is a Peavey part number. PV will sell some to you, or you could order generics - MJ15015 from som ewhere like Allied Electronics. Even MJ15003 would work fine. But chances are very good now that other parts are also bad. The two smaller transistors with their little individual finned heat sinks are suspect. Also ther are a number of small resistors we'd need to check for burnt out condition.

Will do when I get back from vacation (Next Week). Thanks.