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Vintage threads from the first ten years

Poking around...

9/22/2000 9:56 PM
anonymous	Poking around... I just bought this Fender Bassman 50 and I'm curious to look inside and see. Is it safe to just drop the chassis and take a look with touching anything. Don't wanna die ! Thanks.

9/22/2000 10:56 PM
Tubehead	If you don't know anything about amps or electronics, DON'T do it! You could die! Look around on the internet, there are plenty of nice pictures of the insides of amps there, and unless you are using your computer in the bathtub, it's very unlikely you'll die. Good luck

9/22/2000 11:00 PM
anonymous	I just want to be able to get to my cab. It needs re-finishing terribly and I need to know what to do in order to drop the chassis with out harming myself or anything else... Thanks

9/22/2000 11:33 PM
Stan Cotey	I too would recommend not proceeding. However, if you feel you must, here are some ideas you can use. I do not mean to imply that no harm will come to you and I urge you to use common sense and caution. And of course, in no way will I accept responsibility if things go astray. Here's what I would do in your situation. First of course, be aware that there are lethal voltages present inside your amp. With the amp unplugged, the filter capacitors can still store enough charge to harm or at least maim you. All of the old guys talk about the "keep one hand in your pocket at all times" rule, which is a good one. It prevents you from placing one hand on the grounded chassis and t'other on a live voltage source with your heart being the lucky receipient in the middle. If you still want to remove your amp from it's cabinet, I would do it like this: Step 1) Set the amp up as though you were going to play, i.e.- plug the amp in to a speaker as you normally would and your guitar into the amp, etc. Step 2) Switch on the power switch and let the tubes warm up. Then, switch on the standby and play like the wind. Play like you've never played before. Okay, just play loud. Step 3) Then, while you're playing, reach around and switch off the power switch while leaving the standby switch "on". Keep playing -- the sound will collapse and die. Step 4) Unplug the amp from the wall and cautiously proceed with the disassembly. Remove the back panel and the four screws on top of the amp. If your amp has been in a basement for a while, make danged sure you look with a flashlight underneath for spiders, etc. Assuming the filter cap cover (a metal box sitting under the right side of the chassis as you look at it from the rear with rounded corners) is in place, there should be nothing to hurt you exposed under the chassis. You can then slide the chassis out. What you did was to mostly discharge the filter caps by switching off the power transformer. Hawever, they will recharge slightly on their own just sitting there and, you will only discharge them while the tubes are still hot. As soon as you switch off the AC, the cathodes begin emitting less. So the method is not perfect and the caps will still retain some charge. If you want perfection, once the amp is out of its cabinet, grab an aligator clip lead and attach one end to the chassis and the other to a sacrificial screwdriver (that rusty old Craftsman that's been rattling around in your kitchen drawer, for example). Then with the standby switch still in the "on" position -- and the amp most definitely unplugged from the wall (!) -- touch the tip of the screwdriver to either terminal on the standby switch. It should make some degree of spark. After this, the filter caps should be safe. Remember a few things: it's always cheaper to have someone work on the amp who knows what they're doing than to have loved ones figure out how to eat after you're gone. Amps are not sensitive creatures and they will damage you regardless of your karma. It's just the dogma of it. BE CAREFUL!!! If you have any questions about this, e-mail me privately and I'll give you my phone number. I would also recommend not taking my word for it. Let's see if some of the old timers here yell at me first. And like previous wise people have said, if you don't feel a large degree of confidence about this, don't do it!

9/22/2000 11:33 PM

Stan Cotey

I too would recommend not proceeding. However, if you feel you must, here are some ideas you can use. I do not mean to imply that no harm will come to you and I urge you to use common sense and caution. And of course, in no way will I accept responsibility if things go astray.

Here's what I would do in your situation. First of course, be aware that there are lethal voltages present inside your amp. With the amp unplugged, the filter capacitors can still store enough charge to harm or at least maim you. All of the old guys talk about the "keep one hand in your pocket at all times" rule, which is a good one. It prevents you from placing one hand on the grounded chassis and t'other on a live voltage source with your heart being the lucky receipient in the middle.

If you still want to remove your amp from it's cabinet, I would do it like this:

Step 1) Set the amp up as though you were going to play, i.e.- plug the amp in to a speaker as you normally would and your guitar into the amp, etc.

Step 2) Switch on the power switch and let the tubes warm up. Then, switch on the standby and play like the wind. Play like you've never played before. Okay, just play loud.

Step 3) Then, while you're playing, reach around and switch off the power switch while leaving the standby switch "on". Keep playing -- the sound will collapse and die.

Step 4) Unplug the amp from the wall and cautiously proceed with the disassembly. Remove the back panel and the four screws on top of the amp. If your amp has been in a basement for a while, make danged sure you look with a flashlight underneath for spiders, etc. Assuming the filter cap cover (a metal box sitting under the right side of the chassis as you look at it from the rear with rounded corners) is in place, there should be nothing to hurt you exposed under the chassis. You can then slide the chassis out.

What you did was to mostly discharge the filter caps by switching off the power transformer. Hawever, they will recharge slightly on their own just sitting there and, you will only discharge them while the tubes are still hot. As soon as you switch off the AC, the cathodes begin emitting less. So the method is not perfect and the caps will still retain some charge.

If you want perfection, once the amp is out of its cabinet, grab an aligator clip lead and attach one end to the chassis and the other to a sacrificial screwdriver (that rusty old Craftsman that's been rattling around in your kitchen drawer, for example). Then with the standby switch still in the "on" position -- and the amp most definitely unplugged from the wall (!) -- touch the tip of the screwdriver to either terminal on the standby switch. It should make some degree of spark. After this, the filter caps should be safe.

Remember a few things: it's always cheaper to have someone work on the amp who knows what they're doing than to have loved ones figure out how to eat after you're gone. Amps are not sensitive creatures and they will damage you regardless of your karma. It's just the dogma of it.

BE CAREFUL!!! If you have any questions about this, e-mail me privately and I'll give you my phone number. I would also recommend not taking my word for it. Let's see if some of the old timers here yell at me first.

And like previous wise people have said, if you don't feel a large degree of confidence about this, don't do it!

9/22/2000 11:47 PM
Don Symes	Stan gives good advice, to which I'd like to add about a point and a half. 1) Put a sock or rubber glove on one hand and _gently_ remove the tubes before you take out the chassis screws. Place them IN ORDER someplace secure and out of your way. The sock/glove is about not getting oils and sweat on the glass - this can (rare but not unknown) gradually eat its way through and kill a tube. If the tubes aren't in ther chassis, you can't crush 'em when you almost drop it trying to slide it out. 1.2) While you're out getting the wire and 'gator clips, pick up a resistor of 1k ohm (+/- 700) 2 to 5 watt resistor and put this in series with your clip-wire-screwdriver. That short-cicuit discharge is a tough thing on a cap, espescially an old one. 1.3) If you have the money handy, pick up a DVM that can deal with 1000VDC. You can use that to reassure yourself that the caps are discharged. 1.4) Geofex have some good safety info posted. 1.5) When you look under the chassis, if you see can-like structures with wires coming out of their ends - those are the caps you're worried about. Take the amp to someone skilled. Be careful.

9/22/2000 11:47 PM

Don Symes

Stan gives good advice, to which I'd like to add about a point and a half.

1) Put a sock or rubber glove on one hand and _gently_ remove the tubes before you take out the chassis screws. Place them IN ORDER someplace secure and out of your way. The sock/glove is about not getting oils and sweat on the glass - this can (rare but not unknown) gradually eat its way through and kill a tube. If the tubes aren't in ther chassis, you can't crush 'em when you almost drop it trying to slide it out.

1.2) While you're out getting the wire and 'gator clips, pick up a resistor of 1k ohm (+/- 700) 2 to 5 watt resistor and put this in series with your clip-wire-screwdriver. That short-cicuit discharge is a tough thing on a cap, espescially an old one.

1.3) If you have the money handy, pick up a DVM that can deal with 1000VDC. You can use that to reassure yourself that the caps are discharged.

1.4) Geofex have some good safety info posted.

1.5) When you look under the chassis, if you see can-like structures with wires coming out of their ends - those are the caps you're worried about. Take the amp to someone skilled.

Be careful.

9/22/2000 11:53 PM
Stan Cotey	Good points all, Don. Thanks. I use the resistor discharge method so I don't know why I didn't think to write it.

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