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BRAUN SK5 Power Issues AC on Chassis
Old 4 weeks ago
  #1
Here for the gear
 

BRAUN SK5 Power Issues AC on Chassis

Hello!

I'm working with a '58 Braun SK5 (AKA Snow White's Coffin). Single ended, hifi system.

Currently, there is AC voltage on the Chassis. Sometimes as much as 60v, usually close to 6v, and once I had all 120v.

Whats been done thus far:

1. New tubes are installed
2. C49 and W27 on the power EL84 power tube replaced
3. Most resistors are testing well enough for their age and haven't drifted too far


If anyone has worked on one before, what other capacitors could potentially be leaking this much AC to the chassis?

My first thought was a death cap that is on the AC side of the diodes that was leaking, however the schematic doesn't read a death cap.

Attached is the schematic.

Thanks for any help!
Attached Thumbnails
BRAUN SK5 Power Issues AC on Chassis-braun_sk5_sch_better_quality.jpg  
Old 4 weeks ago
  #2
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Radardoug's Avatar
 

Only a 2 wire power cord shown on the schematic. Have you put a proper ground on it?
Old 3 weeks ago
  #3
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Quote:
Originally Posted by Radardoug View Post
Only a 2 wire power cord shown on the schematic. Have you put a proper ground on it?
I have not. I was warned that any AC on chassis is problematic and the fix is not as simple as a grounded cable.

Is this correct?

I've replaced dozens on guitar amplifiers, but this is my first time working with a live chassis.
Old 3 weeks ago
  #4
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Radardoug's Avatar
 

That amp uses a transformer, so the chassis should not be live. You are probably measuring leakage. Try this. Unplug, put an ohmeter between the chassis and one of the mains input wires. This should read very high, many megohms. If it does, just ground the chassis with a third wire. If it then blows the fuse, you have a leaky power transformer.
Old 3 weeks ago
  #5
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JohnRoberts's Avatar
 

If grounding the chassis blows a fuse you have a real problem, if not it may just be high impedance stray leakage.

Did this just begin, or might it have been like this for some time?

JR
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