Idea for safely discharging capacitors.

[SoulFetish]

At the risk of mongering another Rod Elliot article... well, here is another Rod Elliot article touching on these very themes:

https://sound-au.com/articles/bleeders.htm

[Axtman]

Dave Jones of EEVBlog talks about using a multimeter to discharge capacitors.

https://www.youtube.com/watch?v=vXeZVGMzExw

[loudthud]

Ever wonder why a guitar amp will hum like crazy if the heater center tap becomes un-grounded ? Lift the ground and measure AC Volts between center tap and ground. (Good idea to remove all tubes first.)

[J M Fahey]

Dave Jones of EEVBlog talks about using a multimeter to discharge capacitors.

Well, if you are not in a hurry, why not?

Just imagine the time constant involved considering Multi meters typically have between 1M and 10M input impedance.and, say, 50uF (or larger) supply caps.

Hey, excellent way to grow a beard

[Helmholtz]

The hysterical guy in the video describes 2 methods to discharge a cap with a meter:

1) Using a meter having an Auto-Lo-Z feature.
2) Using the Ohm range relying on the meter's protection circuitry to discharge the cap.

Nothing I'd generally recommend.

[Helmholtz]

Ever wonder why a guitar amp will hum like crazy if the heater center tap becomes un-grounded ? Lift the ground and measure AC Volts between center tap and ground. (Good idea to remove all tubes first.)

Yes, you will see a substantial ghost voltage with a high impedance meter due to capacitance between PT windings.
To distinguish from a "real" voltage (meaning a voltage that can supply some power) meters for electricians often have a low impedance mode.

[R.G.]

I realize that this is an issue for a tech who has to work on any old amplifier, whether it was well thought out or not. For any amp I build or repair, I insert a bleeder resistor across each deadly cap, setting the value to dissipate maybe 1/4W for a half watt resistor at full voltage. Discharging caps on am amp with this addition is then never an issue again. For extra points, put an LED in series with the resistor so you can see that there's still voltage on it.
The additions for actively sensing voltage and discharging it suffer from the same problem - they are not already included in most amps. A resistor is cheaper and more reliable than an active bleeder.

[SoulFetish]

I add bleeders as well, although not on every cap. Still works so long as the you remember to flip the standby switch in some Fender type models.
but even so, I really try and stay diligent and manually discharge them as a safety redundancy.
The first bleeder rig I used went open without realizing it for a while! (Yikes!)
Now I use this 2k/50W setup (I ended up happening upon a box of these resistors for free at some point).

[The Dude]

I always check voltage across caps with a meter, even after discharging, to make sure.