Wiring in some filter caps

[Matt300ZXT]

I'm almost done with my Red Bear refurbish. Assuming I didn't wire in a preamp tube socket incorrectly, or a power amp tube socket with those huge thick wires incorrectly (don't want to burn my house down). Also, hopefully I hooked the pots up correctly so that my EQ works as it should lol

Anyways, I'm about to make/mount my custom board for my new axial style JJ filter caps since they don't make the type of caps my amp came with anymore and had a question that was confusing me a little and want to make sure I get this absolutely perfect.

I understand that the type of cans I had used the body to ground themselves through the nut that secured them to the chassis and the 1 lead was the positive, so when I mount these, I'm just going to ground the negative leads on all 6 caps and not even worry about that part, but I'm kind of confused as to why some of the positive leads also lead straight to ground and some are grounded through resistors.

I'm going to follow my notes and obviously re-route a couple wires due to a whole new filter cap section going in, just looking for some clarification as to why some positives are grounded. It's just one more nugget of information I can store away for myself.

[xtian]

Note that the copper on those plates under the original caps are not grounded, unless they are specifically wired to ground! So, for example, the cap in the upper left is not grounded directly--it's negative lead is connected in series with the positive lead of the cap just below. On the right, those resistors that you suggest are connected to ground are just connected to the copper plate...you need to reevalute what you're looking at with this in mind.

[Phil_S]

Why did you ground the + terminal on some of those caps?

[Matt300ZXT]

I haven't touched any caps in the amp yet, I only did the pots and sockets and copied exactly the way they were before I got in there. The picture shown is how the amp looked before I even started doing all this.

I'm actually working now on a design to lay out the caps so that I can hook wires up properly with as little wire replacement as possible.

As far as the copper plate, it's a little hidden but there are little ground wires going from the lower ones to solder tabs that are on the bottoms of standoffs to ground the plate.

[Matt300ZXT]

I see what you're saying Xtian, I didn't notice the break in the copper, the 2 lower squars go to ground but I see what you mean by the ground plates of the top 2 being tied to the positive leads of the others because they don't ground themselves.

To copy that, do I just need to ground those 2 caps, then run a second wire to the positive leads of the other 2 caps, or run only 1 wire from the negative straight to the positive of the others?

I did some wire tracing:

Top left cap-2 white braided wires go to the rectifier and the other to the h.t. fuse

Bottom left cap-1 white braided wire to the stand by switch, the purple wire leads to a cap on the power board

Top middle cap-1 yellow wire to choke

Bottom middle cap-none

Top right cap-1 white wire to the preamp board

Bottom right cap-1 red wire goes to a lead on a preamp tube

[xtian]

I think you've got the idea now, Matt. It's always best if you have a schematic to compare against, but I understand the situation.

[Matt300ZXT]

Here are better schematics. Can't remember if I posted any in my last thread about what caps to buy but this is a very clear, easy to read set of schematics since Xtian requested I post them.

[xtian]

Yeah! That PDF schematic clears up the wiring. Very good.

[Matt300ZXT]

Here is my extremely rudimentary drawing lol I think this is how I'm going to lay out the caps on my board.

If you guys can verify I got those things laid out smartly that'd be awesome. It seems I got all the wires run from the proper component to the proper cap (copying the old layout I took notes on), just looking to see how to exactly wire those 2 negative terminals that tie in to the positives of other caps and I think I've got this amp done.

[Phil_S]

LOL, joke is on me. Those two caps with + to ground must be for the bias supply. I'd have never suspected can caps for a bias supply. Thanks for remembering to tell us that was how you found it -- its original state. I'm going to be a spectator for a while on this one. Xtian seems to have this well in hand.

[Matt300ZXT]

Oh, in case someone is curious why I labeled the caps with 1-6 and not in order, in notes I took before taking it apart I labeled the caps as 1 and 2 for the top left and middle, and 3 and 4 for bottom left and middle. The two off to the side w/o copper plates I labeled as 5 for the top and 6 for the bottom.

I was writing that stuff down for my own notes in my head so you don't really have to pay attention to the numbering I gave the caps.

[xtian]

Yeah, um, sorry. There's no way I can confidently say you've sketched correctly. Go over every point three times, make sure it has the right number of connections to other components, and that each connection is correct. Then turn the drawing upside down and do it again. Then repeat the process tomorrow.

[Matt300ZXT]

Perhaps I should have posted a pic of the actual board I installed so the drawing makes a bit more sense. Since I'm having to go with this layout since I didn't wanna go with radial caps that were available, I'm going to lay the 6 caps out along this board, hence the drawing I made with the various wires going here and there.

Were you able to tell by the schematic, Xtian whether those 2 caps need to be grounded AND tied into the positive of the other caps, or tied in to the positives of the other caps only?

[xtian]

Were you able to tell by the schematic, Xtian whether those 2 caps need to be grounded AND tied into the positive of the other caps, or tied in to the positives of the other caps only?

This is what worries me, Matt! It's right there in black and white. Look at the schematic, but don't trust it--compare with the amp as a reality check.

I'll do this first one for you. I marked three spots on the schematic, and marked the corresponding spots on the photo. Can you see how this works?

[schaublin65]

Hi,

this might be obvious to you. If it is, then forgive me for pointing it out.

Those filter caps are "stacked" in series between the B+ and ground.

The schematic shows a B+ of 394 volts. Too close to the limit for 400 volt caps. Stacking them gives you an 800 volt limit.

The 220k resistors are there to equalise the work they do.

Hope you knew that. No harm meant by spelling it out.

Take care.

John