Safety First... Tips?

[Tim.]

Being new to all of this and very interested in the inner workings of amplifiers, I would like a few safety guidelines from our community here.

regretfully, i am not dinking around with a tube amp right now. here's what i have:

marshall lead 100 mosfet

main problems:
the pots have dead spots, faded spots and are scratchy.

i would like to take the amp apart and clean the pots if possible and replace if needed.

as of now the amp has been unplugged for 23 hours. i really dont know how long they can hold energy. a solid state amp in this case...

so, how-bout it? what should i watch out for?
thanks!
tim

 

[Cygnus X1]

SS amps don't hold much electricity in the caps.
Just make sure it's unplugged.

Buy some deoxit spray, spray into the back of the pots, and rotate vigorously.

Don't use WD-40.

 

[Tim.]

SS amps don't hold much electricity in the caps.
Just make sure it's unplugged.

Buy some deoxit spray, spray into the back of the pots, and rotate vigorously.

Don't use WD-40.

been waiting all day for someone to chime in

also watched a bunch of safety vids and looked up some rules but all for tube amps.

i didnt see anything about discharging capacitors (tube amps) that is something i want to know about too. it gets mentioned but i didnt see any good info.

im off to dive into that amp! thanks

 

[Cygnus X1]

Don't look forward to replacing the pots, could be major surgery on that amp.
Probably board mounted...I wouldn't want to do it.

While it's open take a REAL CLOSE look for any little resistors that look like they have gotten too hot and caps that may be bulging.
Should be OK, but always best to check.

And use your nose, it should tell you very quickly about the health of the amp.

 

[Tuya Customs]

Sorry for the the thread jack, but cyg, how long do tube amps hold charge? I'm tweedifying my champ this week.

 

[Tim.]

Sorry for the the thread jack.

no problem.. stuff i wanna know too

 

[Birdy]

Pretty good vid for toob noobs. Basic for some, rocket science for others.

Mesa Boogie Tube Troubleshooting 101 Video

 

[Cygnus X1]

Depends on the power supply setup.
5 minutes to several days!

Had an old PA amp that refused to give up the charge on the caps unless discharged
directly.
Don't use a screwdriver kids!

 

[Standard 64]

SS amps don't hold much electricity in the caps.
Just make sure it's unplugged.

Buy some deoxit spray, spray into the back of the pots, and rotate vigorously.

Don't use WD-40.

rotate the pots vigorously,not yourself!!!!

 

[LPV]

Sorry for the the thread jack, but cyg, how long do tube amps hold charge? I'm tweedifying my champ this week.

Discharge them. It's a good habit to learn. Just make sure to do it safely.

 

[Tuya Customs]

Discharge them. It's a good habit to learn. Just make sure to do it safely.

How?

 

[Cygnus X1]

Heavy neoprene or rubber gloves, and an alligator clipped lead holding a 10 watt 1K ceramic resistor.
[EDIT] (D'oh):
Any plate to ground will work.
(Pin 1 or pin 6 of a 12AX7 type tube for example).
Leave it clipped in place while you work on it.

I always probe with the meter in various spots to make sure.

And don't forget to remove it prior to startup!

 

[LPV]

This is what I do. You have to decide what method you feel safe with yourself. I use the resistor wire as cyg mentioned with alligator clips and connect one side to the chassis then clip one end to the tip of a chopstick. A hand behind the back and touch the cleanest access to a plate pin or positive side of a filter cap. Keep it on there for a minute and then check the voltages. Make sure that your meter is looking for dc voltage. If you have it on AC it will read 0v even if there is a charge. Seems obvious but I did it.

 

[hipofutura]

How?

I use a pair of 100 ohm 10W resistors. Radio shack sell the resistors (2 per pack) and the alligator clips.

Take one alligator clip and cut it in half. Solder one to each resistor. Then jumper the two resistors together on the other end. Wrap with electrical tape and you're done.

 

[FLICKOFLASH]

Good & much needed thread

 

[FourT6and2]

I just use a wire with alligator clips. No resistor as the resistors in the bias supply will keep the caps from draining too quickly. I place one end on pin 1 of V1 and the other end on the chassis. Wait a few minutes and you're good to go.

This method will depend on the amp, though. The amp I do this on is a Marshall Super Lead.

You can wire up a resistor in series with the clip if you want, I guess.

 

[coldengray]

a lot of amps have bleed resistors built in, but it's imperative to still check and be able/prepared to drain the caps yourself.

 

[Liam]

I always go for grounding pin 1 of any on the preamp tubes as Cygnus has suggested. Also leaving it in place, as with some amps the caps "grow back" the voltage after you've drained them. Some sort of weird electrolytic memory effect...

But back to working on solid state amps. Stay away from the AC power supply when it's plugged in. The rest of the circuit will be relatively low voltage, just don't lick anything or work on it in the bath - you'll be fine.

Liam

 

[Tim.]

Really appreciate the tips and safety rules so far. Anyone has more safety questions to ask, please do so. Many of the less experienced like me would be so grateful.

Btw, got my amp back together and it is much the better after my tinkering. Everything inside looked and smelled normal and the pots cleaned up nicely.

 

[SteveGangi]

Here's a basic tip that doesn't require any "special tools and gizmos", and yet it is one of the most important.

Always work with only one hand. Keep the free hand well away, in a pocket if you have to. That way you never become part of the circuit. You may still get "bit" once in a while but you get to talk about it later.