Draining Filter Cap Question

[boyt_bpc]

OK, I've been doing this for over 30 years. What strikes you as a bad idea? Essentially, you drain the caps through the speaker load. You need to provide a signal in order to help the caps drain faster, so I use the hum from an open cable being held in my hand. It could be from a guitar or signal generator as well. Best of all, it's totally non-invasive and does not require thinking about where to place a bleeder resistor. If the amp, by some chance, will not power up, the caps are probably discharged anyway.

And, like I said, I ALWAYS double-check when I open the amp with my DVM, and you (meaning everybody) should too!

The reason I said that was because not all amps will drain the caps that way, so it doesn't always work. Not all amps have bleed resistors.

[Bruce / Mission Amps]

I don't think there is anything wrong with John's method either.
I do the same thing with my signal gen when working on my bench.

The real downside is that the tube amp must have hot vacuum tubes in order for them to work and drain off the B+ rail.
If you flip an amp on and off too fast, the rectifier will charge up the hi-voltage caps instantly if solid state (and very quickly with a rectifier tube)... but the other tubes might not heat up and will not conduct!
So then the filter caps do stay charged up and can give you serious poke.
Just respect that and the method John is stating is fine most of the time.

[jrfrond]

.....And, like I said, I ALWAYS double-check when I open the amp with my DVM, and you (meaning everybody) should too!

There's a good reason I said this.

Use your head, and you'll get to keep it.

[boyt_bpc]

There's a good reason I said this.

Use your head, and you'll get to keep it.

It sounds like the common knowledge is "It works" but the mantra in learning is "Don't do this."

[jrfrond]

It sounds like the common knowledge is "It works" but the mantra in learning is "Don't do this."

I've been repairing and building amps, guitars and drums for 30+ years. I'm involved in electronics, woodworking, metalworking, finishing, power tools (some potential very dangerous) and I have made and gotten away with more stupid and dangerous (personally) moves than I care to count. I don't advocate the use of dangerous practices, but every experienced tech does it, and occasionally pays for it (a few with their lives). This is why I recommend the DVM-backup approach to ANY method of cap discharge, whether it is my down & dirty method, or the bleeder resistor approach. I was once on the receiving end of a paramedics' defibrillator paddles from a massive shock when I first started in this business, and now have a healthy respect for electrical current. You should too. THAT is the proper school of thought.

[boyt_bpc]

I've been repairing and building amps, guitars and drums for 30+ years. I'm involved in electronics, woodworking, metalworking, finishing, power tools (some potential very dangerous) and I have made and gotten away with more stupid and dangerous (personally) moves than I care to count. I don't advocate the use of dangerous practices, but every experienced tech does it, and occasionally pays for it (a few with their lives). This is why I recommend the DVM-backup approach to ANY method of cap discharge, whether it is my down & dirty method, or the bleeder resistor approach. I was once on the receiving end of a paramedics' defibrillator paddles from a massive shock when I first started in this business, and now have a healthy respect for electrical current. You should too. THAT is the proper school of thought.

I am of the belief that, if it can kill you, don't take the shortcut.

[Enzo]

The bottom line is we want to empty our caps. Whatever method you chose, if it works and you check with a meter, then IT DOESN'T MATTER WHAT THE METHOD IS. We can endlessly debate whose method is "better," but if it works it works. The fact that someone like John seems comfortable doing it doesn't detract from its efficacy. I may seem nonchalant doing my benchwork as well. Doesn;t mean I am not aware of the safety issues, they are part of my routine. I feel a lot safer relaxed and confident in my approach than being all tense, uptight, and fearful.

[boyt_bpc]

The bottom line is we want to empty our caps. Whatever method you chose, if it works and you check with a meter, then IT DOESN'T MATTER WHAT THE METHOD IS. We can endlessly debate whose method is "better," but if it works it works. The fact that someone like John seems comfortable doing it doesn't detract from its efficacy. I may seem nonchalant doing my benchwork as well. Doesn;t mean I am not aware of the safety issues, they are part of my routine. I feel a lot safer relaxed and confident in my approach than being all tense, uptight, and fearful.

Agreed.

[chordfinger]

when you make your own cap drain tool can you put an LED after the resistor going to ground for visual progress purposes? thanks