Getting inside of the Rebel 20

  • Thread starter Thread starter RichieGB
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RichieGB

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This question is probably very newbie but it's important to me.

I'm learning about the inside of my Rebel 20. It's developed a hum that I want to investigate, and I have some common problems I would like to take a look at before sending off to repair. But I'm new at amps, and so before I can get in and start checking things, my first priority is safety. Specifically, I want to make sure I'm doing a proper drain of the power supply filter caps.

I understand that I can do this by using pins 1 or 6 of the V1 tube:
XJ7JCe7.jpg


Is this accurate? I turned off and unplugged the amp, then measured between pin 1 (or 6) and the chassis and it only read around 5-7 VDC...pretty small. The measurement drops even lower by applying a resistor between pin 1 (or 6) and the chassis, which I would expect.

Does this mean that the power supply filter caps are drained and the amp is safe to work on, or am I missing something? Thanks in advance.

P.S. I am doing this all with one hand in a pocket, as many suggest.
 
Hi RichieGB,

Seems like you are on top of things. Make sure that the standby switch is in the Play position (as if amp were ready to play), and I would check each preamp tube pins 1 and 6, and each output tube pin 3 to be sure all voltages are drained, and you should be good to go.
 
Richie, drain the filter cap AT the filter cap.
Use googles, dielectrics can explode.
Use a wooden amp jig to hold chassis on carpeted floor, use rubber soled shoes. The ground you are standing on may be at the same electrical "potential" as the chassis.
Yes, you can be electrocuted with only one hand in your amp.

Use a 25k 10watt power resister & a HT pliers. Bend leads similar to caps and touch lead to lead.

How long? T=R•C
T being time
R being resistance in ohms
C total capacitance of all caps. Usually wired in parallel.

Try and work with someone around.

I know this sounds overly cautious, and I've seen old hands discharge caps with a screwdrivers.

I think they are stupid..
 
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