1960's Kustom K100 Amp - Trouble after repair - PSU Q's

[anticpunk]

Hey,

I opened the amp to remove the deathcap and install the new grounded power cord, and I found a huge mouse nest (guess how long it's been since I've used this one). The vermin had eaten alot of the wires. After cleaning out the mess and repairing/replacing the affected wiring, I decided to install some new power supply filter caps. I had been noticing some pulsing of the power indicator when I ran the amp at high volume and played chunky low notes, so I went for them first since they are basically the only electrolytics in the whole amp.

Anyway, long story short, I finished it all today, hooked it to my cab, threw the new switch to the on position and it took a fraction of a second for the power light to come on (it always just sprang to life before) and I have no audio, just a big loud low-endy mmmmmmmm.

Looking inside I don't see any misconnected wires or anything broken/out of place.

Questions:

Could replacing the power supply caps have effected the circuit in a negative way?

Is it possible that the mice nesting in side could have screwed up something more sinister than just the wiring?

I can't find a source for the schematic, so I'm hoping maybe someone here has some experience with these as I am stumped on this one and don't mess with amps all that much.

Any help would be much appreciated as usual,

Thanks!

Jay

[creaturesleeper]

Hey,

I opened the amp to remove the deathcap and install the new grounded power cord, and I found a huge mouse nest (guess how long it's been since I've used this one). The vermin had eaten alot of the wires. After cleaning out the mess and repairing/replacing the affected wiring, I decided to install some new power supply filter caps. I had been noticing some pulsing of the power indicator when I ran the amp at high volume and played chunky low notes, so I went for them first since they are basically the only electrolytics in the whole amp.

Anyway, long story short, I finished it all today, hooked it to my cab, threw the new switch to the on position and it took a fraction of a second for the power light to come on (it always just sprang to life before) and I have no audio, just a big loud low-endy mmmmmmmm.

Looking inside I don't see any misconnected wires or anything broken/out of place.

Questions:

Could replacing the power supply caps have effected the circuit in a negative way?

Is it possible that the mice nesting in side could have screwed up something more sinister than just the wiring?

I can't find a source for the schematic, so I'm hoping maybe someone here has some experience with these as I am stumped on this one and don't mess with amps all that much.

Any help would be much appreciated as usual,

Thanks!

Jay

I would check the Polarity on the caps just to make sure you didn't accidentally reverse one....and make sure the cord is grounded right...the green wire should go to chassis and the white and black wires to the fuse and switch...Also did you turn this on before you made changes and did it hum than? I looked on schematicheaven.com and they didn't have one either...

[anticpunk]

hey!

Thanks for the reply.

I will pull it apart again and recheck the caps.

I have done the cord/deathcap mod on several Kustoms before with never an issue.

I used this a bunch of times in the past and it had just a tiny hum in the noisefloor when the guitar was muted. Other than that, it was lacking a little lowend and the power indicator dimmed when I hit hard chords. Figured the caps were crapping out due to age, so it seemed like a logical move to replace the big electrolytics.

I'll let you know what happens when I open it again.

Thanks!

Jay

[anticpunk]

Update:

I checked polarity on the caps, all looks right.

The center tap on the secondary is connected to the chassis connection and also the heatsink for the power transistors ties their cases to gnd also.

Is it possible that the center tap or heatsink bond could be looping?

The circuit layout at the "PSU" section:

Rectifier + to c1 + and off to circuit
c1 - to c2 + along with the CT connect and the Chassis connect at the output jack
Rectifier - to c2 - to circuit

These connections were done 1 for 1 as the old caps came out.

Seems like a simple thing........... If thats a little unclear, I can post a schematic that I made of the current connections.

Thanks Again!

Jay

[Scodiddly]

Bad rectifier? Massive hum and no audio would be the result of that.

[creaturesleeper]

Bad rectifier? Massive hum and no audio would be the result of that.

Word! If you have a tester check your voltage after the rectifier diodes it should be some high DCV and no ACV. Also check the individual diodes for continuity...they should pass voltage one way but very little the other way... Also there should be a voltage drop of about 1.5 volts after each one and remember they reverse the voltage so reverse your leads or you'll see a voltage gain!I'm assuming this amp probably has some sort of diode rectifier. As you know a schematic would be nice! Also go to el34world.com for a wealth of info on troubleshooting amps in general. I found this site to be extremely valueable. If this is your problem Diodes are very cheap..
Good luck!

[anticpunk]

Hey, thanks again for the info!

It has a large bridge rectifier that mounts to the chassis near the transformer. I have a standard DMM and a Fluke so between the two I should be able to suss that out.

I'm not really sure why it takes a second to power up the light, I would figure that since the caps are just cleaning up ripple, they wouldn't have to charge before the circuit got power, sound miswired no?

Also, is the grounded center tap normal?

I have a 7A bridge rec that I'll replace the original with, Should be substantial enough right?

Thanks,

Jay