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K50 [message #28446]

Fri, 11 February 2022 10:52

pleat
Messages: 1454
Registered: June 2004
Location: Belding, Mi

Senior Member

After all these years on this forum, I have a K50 amp that was working and sometimes would go into a loud hissing/frying bacon sound, then all of a sudden the amp won't pass a signal. The amp will produce the crashing reverb sound if shaken. I used to have a repairman in my area, but he has retired. I have three K50's and one of my other amps is starting to produce a slight background hiss that comes and goes at random. I've used the K50's as my main gigging amp for the last 24 years and I need some help getting at least one back up and running. Any thoughts?
Thanks
Pleat

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Re: K50 [message #28447 is a reply to message #28446]

Fri, 11 February 2022 12:03

JDinPA17603
Messages: 69
Registered: May 2018
Location: Lancaster, PA

Member

Question 1. Is it still hissing?
Fact that you hear the reverb crash shows driver/output/power supply is good. Means issue is mainly in the preamp section. I haven't had one of these on my bench yet, but my first guess would be the FET 2N5033.
I believe Stevem and ChicagoBill have had experience with these. I only see a schematic for the K50-2 on the board here. Hope this starts you in the right direction. Do you have any tools/soldering skills/ test equipment?
John

Old Us Navy Vietnam Vet
Playing for my own enjoyment and irritation of the neighbors.

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Re: K50 [message #28448 is a reply to message #28447]

Fri, 11 February 2022 13:59

pleat
Messages: 1454
Registered: June 2004
Location: Belding, Mi

Senior Member

No, the K50 is now dead silent, but will amplify the crashing reverb sound if struck. Chicago Bill repaired a K50 for me a few years ago. I am more a kustom historian, having used Kustoms and sold Kustoms since 67. Not a tech by any measure.

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Re: K50 [message #28449 is a reply to message #28446]

Sat, 12 February 2022 07:17

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

The volume pot in these amps is before the first gain stage which is that 2n5033 FET, so if it's bad then cranking out the volume pot will not increase the hiss level heard.

That could be bad , or the filter caps C6 and or C5 could be fully bad or leaky.

A lot of FETs that in general good bad in amps and stomp box's I find are taken out in Winter time by clothing produced static discharge .
Keep in mind it takes at least 1000 volts to jump a gap between you finger and door knob or wall light switch, and no FET will stand up to that!
If you can not find a tech / repair location close enough to you and if you are willing to take out the chassis you could send it to me, or maybe Bill can help you if he is closer , or maybe even John here is willing?

If any of these small filter caps are have gone south, or are going south then all of them should get replace, in fact one of these starting to go leaky could be what has sent that FET to its grave!

[Updated on: Sat, 12 February 2022 07:24]

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