Replaced Ampeg VT40 cap cans with non-insulated cap cans, ouch!

[Charlie Wilson]

Well, I learned something the hard way when I was replacing the filter capacitors in an Ampeg VT40. I replaced the originals that have a cardboard sleeve on the outside with ones from CE Distribution that do not. The cap cans are in series with 100k bleeder resistors going across each one and each cap is on an insulated plate. I found out the hard way that since the first cap is not grounded that there is voltage on the negative non-insulated outside of the cap can. I am going to try and get the cardboard sleeve off of the originals and put them on the new caps but it makes me wonder how many guys have recapped their Ampegs not knowing that one of the cap cans will shock them if touched.
CW

[TUBEDUDE]

Covered in the sticky at the top of the technical discussion:

Screenshot_20211210-050444_Brave.jpg

[Stevem]

Yes. They are stacked!
Lesson learned right?
Use can use the inner paper tube from a toilet paper roll, or Trim up a tall paper coffee cup like from McDonals.

[sluckey]

Back in the b&w tv days it was very common to see a mix of cap cans on a chassis. Some were bare metal cans and those used a metal mounting plate, while others had a cardboard cover over the can and those used a phenolic mounting plate. Didn't take long to figure out why. At that time cap cans were cheap but they came in a box that included one metal mounting plate and one phenolic mounting plate. The phenolic plates were easy to break when changing a cap. The box of "extra" screws under the bench also contained plenty of these mounting plates. Now days you pay a premium price for these cap cans and have to pay extra for the mounting plates. At least you can still get some of the more common values.

[xtian]

All the cap cans I've seen in 50s and 60s amps are riveted to the chassis. How did they expect people to replace them?

[sluckey]

All the cap cans I've seen in 50s and 60s amps are riveted to the chassis. How did they expect people to replace them?

It's the mounting plate that is riveted, not the can. The can has twist tabs that slip through little slots in the mounting plate. Then you slightly twist the little tabs to lock the can to the plate. One or more of the twist tabs are usually soldered to the plate to complete the can installation. To remove the can just remove the solder from the twist tab (not always easy and requires a big gun). Now straighten all the twist tabs and pull the can off the mounting plate. Many times it's easier/quicker to just break the tabs off. The mounting plate stays attached to the chassis and is reused. No need to bust the rivet.

The can in this pic has been replaced and the mounting plate is still riveted to the chassis and was reused...

http://sluckeyamps.com/sunn/sceptre1.jpg

Hammond usually did not use riveted mounting plates. They simply stamped a hole in the chassis. Like this...

http://sluckeyamps.com/hammond_2/big_guts.jpg

[Stevem]

When I was working on TVs the zap from a hot shell of a can cap was only second to the 22,000 volt zap of the anode of the CRT !

[Charlie Wilson]

Yeah, lesson learned. The weird thing is the outside of the cap can had about 600v on it and it shocked me but a pretty minor zap. I'm going to consider that an early Christmas present. I was able to get the cardboard sleeves off of the original caps. The caps are gooped on the inside but they come off pretty easily. Just know that paper sleeves are not an ideal insulator. I can measure between 5-10 vdc on the outside of the sleeve when the amp is on. Ampegs are a little sketchy safety wise.
CW

[martin manning]

"The burned hand teaches best. After that, advice about fire goes to the heart." - J.R.R. Tolkien