Silverface Vibro Champ recap question

[Beyer160]

I recently picked up a '73 Vibro Champ and am planning on recapping it. It's all original and actually sounds pretty good, but there's a little hum and I want to do a tonestack bypass mod (Silverface Champ mods?), so I figure I'll do the caps while I'm in there.

My question is what to do about the can cap. There seem to be three schools of thought on this-

1. Get an exact replacement from CE
2. Kludge a JJ cap in, although it's too large to fit in the stock hole
3. Make a bundle of individual resistors

I'm leaning towards the CE can, but only because I can't figure out how to mount the JJ without reaming out the hole. I've heard of people disconnecting the stock Mallory and leaving it in for aesthetics, and mounting a JJ inside the chassis. Has anyone here done this?

I'm also planning on replacing the cathode resistor.

Thanks!

[Enzo]

The caps probably do need refreshing, but this is a single ended amp, and they will be hummier than push pulls. Not only that, the plate supply comes right off the rectifier - the first B+ node, so that also results in more hum than we are used to. Point being, you may replace every cap within a city block and still have some hum.

I like method 3, though I think you mean a bundle of capacitors. A 20uf (more likely 22uf these days) 450v cap is the size of my pinkie, like the size of a skinny 12AX7 might be. Plenty of room for them. I would cut off the terminals from the old cap and leave the can there for appearance. The three caps can be soldered directly to the eyelets on the end of the board, where the can cap wires are now. Then gather their negative ends together, and solder them to one of the ground tabs on the old can. Or better yet, to the ground lug where the red/yellow power transformer wire is grounded.

It is only three caps. SOmetimes I mount a small terminal strip to make things easier. But that is just me, you may not want to.

Personal choice - I try to avoid can caps unless I have no other option.

I have mounted JJ type can caps under the chassis, yes. Not on a Vibrochamp, but does that matter? I generally mount the can clamp on a side wall of the chassis so the can sticks in towards the center from the wall. Run wires as needed.


And lastly, mounting a JJ on top in place of the can. The JJ doesn't have to fit THROUGH the hole, it only has to fit OVER the hole. Position the clamp so the cap terminals are centered in the hole and not touching the edge. And then mount the clamp in that position. If woried, you can insulate the hole edge with some grommeting material.

[Beyer160]

Wow, thanks for the detailed response!

I'm actually surprised at how quiet it is with the original 39 year old caps, but I don't see any harm in replacing them. It may sound silly, but I don't want to drill a hole in the chassis for a can clamp for the JJ- I generally consider musical equipment to be tools not investments, but I've hacked up enough gear over the years that I kinda want to keep this one unmolested. The tonestack bypass mod is easily reversed, but a hole is forever. I was a little hesitant to stuff extra caps in the chassis in lieu of the can (yes, I meant caps in the original post: note to self, don't post at the end of a long day), but you have a point that they're small enough to fit easily. That's probably what I'll do.

[madkatb]

If you want to get really funky...
Rebuilding Can Type Electrolytic Capacitors | Stereo Raven
Mouser has Nichicon 22uF/450V electrolytics that measure1/2"x1". Vibrochamp pictures that I googled show the can to be bigger than an octal socket (so, bigger than 1") and approx 2"+ high. So, you could fit three inside.
Mouser also sells capacitor clamps that could nicely hide the "cut" and secure the can.
I stacked caps inside a can that I drilled out on a small amp I modded for a friend. (Don't drill the can out. The walls are very thin aluminum.)

[Riffraff]

I replaced mine with individual caps as Enzo mentioned. It was a snap. You should also consider replacing the 2W 470 ohm resitor that is paired up with a 25uf cap just after the power supply connections on the board. That resistor tends to drift and get really hot which eventually takes it, the cap next to it and your power tube out when you push the amp....usually in spectacular fasion.

[Beyer160]

You should also consider replacing the 2W 470 ohm resitor that is paired up with a 25uf cap just after the power supply connections on the board. That resistor tends to drift and get really hot which eventually takes it, the cap next to it and your power tube out when you push the amp....usually in spectacular fasion.

I was already planning on replacing that cathode bias cap & resistor, but thanks for the heads up!

I've been traveling so much for work lately that I haven't had time to even order the parts yet, it'll probably be another month before I get to working on it. It's waited this long though, another 30 days shouldn't hurt.

[riz]

I love my Vibro-Champ! I used the CE can when I rehabbed it, but I must say that in most of these I've worked on, for other people, the original can was still working fine... I like the discreet caps for replacement most of the time.

I left mine alone, but in other, similar amps I have had good luck rebuilding the heater supply with an elevated artificial center tap (two 100-ohm resistors grounded to the top of the 6V6 cathode resistor) as a way to get rid of some of that hum. Like I said, your can cap just may be doing it's job, so you may have to look elsewhere in the circuit to reduce the hum.

[schoolie]

I wanted to keep my Vibro champ looking vintage, so I just installed a small set of radial capacitors

[guitician]

Be sure to let us know how it effected the tone after you replaced them....

[Beyer160]

Be sure to let us know how it effected the tone after you replaced them....

Wound up getting busy with other stuff and never got around to it! As I said, it sounds fine I just figured it was good preventative maintenance. It's still on my back-burner project list, but there's a whole lot of stuff before it.