Is there a proper way to ground out a solid state before servicing

[12pack]

Howdy - I've been lurking for some time here and haven't posted very much at all. I'm educating myself as much as I can on amps repair in general and reading tons of books and other internet available stuff.

With a Tube amp - I've learned that if you jump pin 1 from your preamp tube to ground you slowly drain the current that is left in the amp (typically).

Is there a way with solid state amps that apply to drain the entire amp from hidden voltage for servicing as well?

Thanks

[Ronsonic]

Not usually an issue. Most solid state gear discharges itself gracefully.

If you've got something that doesn't grab a clip lead and a resistor say about 1K per volt to avoid sparks and surprise.

[donnyjaguar]

I've designed low-current solid state communications gear and you have to specifically design it to *not* drain the current when unpowered. Ie: using two transistors where you'd normally use only one; routing grounds through a common NPN transistor etc. I seriously doubt a musical instrument amplifier would employ these designs. It should be drained to nothing after a minute.

[andrekp]

"Should be" and IS are two different things. (Granted SS amps are often safer but...)Before you crank open ANY amp you should have some idea how to drain the caps - or more importantly WHAT exactly NEEDS draining! It's not just a question of knowing some crib of grounding out a particular pin (what type of tube? What type of amp? Is the advice the same? Do you know?)

Whether someone on a forum tells you it will drain itself or not, you should have a multimeter and know how to check for yourself whether it's safe or not. If you are not clear about what all this means, then you need to either have someone who knows show you, or keep it buttoned up.

Seriously - it's not a toy.

[12pack]

Thanks all for the help.

Believe it or not I have a degree in electrical engineering. Problem is that was way back in the 80's and that was the last time I rolled up my sleeves. I've worked on many computer systems right after school and know enough that capacitors can store electricity. I use to short out fly back transformers in CRT tubes even to work on them so we wouldnt get shocked - those really sparked.

I haven't used my electronic knowledge since 1990/1991 as I've been selling software ever since. I am by no means an expert - but I want to blow the dust of my old o-scope and pull apart amps and learn how to repair/recondition them. Without any local amp building repair that I know of - I can't even offer to work for free on weekends just to learn.

I appreciate the advice of not pulling apart an amp to reduce the risk of getting hurt - But I am committing myself in getting educated in amps and their technology.

[Ronsonic]

The good news is that at the voltages and frequencies we see, nothing is going to jump out to get you. So you do get a chance to open it up and measure.

I'm not aware of any solid state amps in our trade that even run a high enough DC to hurt much. The big threat will always be the line voltage.

[Rosewood]

I would always check to make sure. Years ago I welded a screwdriver to the chassis of a peavey cs 800 power amp.

[plexi67]

With a Tube amp - I've learned that if you jump pin 1 from your preamp tube to ground you slowly drain the current that is left in the amp (typically).


Not all amps use 12ax7 tubes[ pins 1 or 6 hs the plate voltage], so it would depend on what amp you are working on. Some amps use other tubes that have a different pinout..
There are simple ways to use a clip lead and resistor to drain the voltage off of an amp. You should be able to find the info on how to make one of these on the internet.. As others posted its always best,no matter what your working on,to hook up your meter,and test the amp in different sections to make sure all voltage has drained from the amp.
The thing is.. in amp repair, you need to have the amp fired up and on,while you check voltages and many other things.. etc..
So you'll also have to learn how to work on the amp while it is plugged in and on.

[PRNDL]

As said by other wise ones, solid state amps usually run at much lower voltages than tube amps (typically 100 volts vs. 400 volts DC).

The electrolytic cap cans, however, do store DC voltage and can spark if shorted accidentally. They do need to be drained if you're going to test them. The good news is they last a lot longer than those punished with high voltage.

Most recommend using a current limiter (light bulb) during initial testing.

[12pack]

Thanks again for all the good advice. I appreciate you all sharing your experience with me.

[Crazy Professor]

In order to drain any stored voltage in any amp, the easiest way is to go to the power supply section, find the main electrolytic (a fixed capacitor consisting of two electrodes separated by an electrolyte), attach an alligator clip with a wire to one of the terminals and touch the other terminal with the other end of the same wire. Caution! Make sure you don't touch any of the electrical parts with your hands, and make sure the unit is unplugged! That is the "raw" way of doing it, you can insert a resistor in series with the wire so the discharge will be dissipated by the Resistor instead of a spark, any value from 10 to 500 Ohms will work. once you connect a resistor in parallel with the circuit hold it there for a few seconds. Note: The main capacitor is usually the biggest in size close to the power supply, there might be two of them. In a solid state amp sometimes there are big capacitors in the output stage.

[donnyjaguar]

I think you'll find there are always two supplies in a solid state power amplifier and at least two biggun electrolytics. Some very powerful amplifiers (300Watts+) take a little while to discharge. You can speed this along by shorting, but like the above, you may end up with a screwdriver welded to the terminals. :)