How/where to place filter caps inside

[alfi27]

Hi guys,

I've been doing the SE Lead mod on my 2204 from 1981, and it sounds great! It's quite an immersive mod and requires two additional filter caps (33uf and 100uf), which are a bit hard to fit. The 100uf has space on the board, and I'll get it fastened entirely with cable ties or possibly glue. The 33uf, however, is just "flying in the air" on a tag strip. Is it possible to put it on the floor of the chassis, and then put some kind of isolation between the cap and the chassis? And could there arise any issues having the 100uf on the board there? I was kind of hoping to not having to extend the leads, but that's inevitable no matter where it's placed...

[pompeiisneaks]

You definitely do not want to leave it hanging in the air like that, vibrations over time are likely to break a lead. If you can lay it flat on the chassis, and silicone it to the chassis that will keep it from moving, then you want to ensure you cover the positive lead with some shrink tube so that it reduces the chance it can touch something and arc. Other than that the negative side, so long as it's directly grounded, can't hurt to accidentally ground a second time so you should be fine there. You just need to make sure both ends of the leads are well connected, which you're doing with the terminal strip.

~Phil

[alfi27]

Thanks a lot Phil, much appreciated! So the capacitor itself can touch the chassis, as long as the positive lead doesn't? It's already grounded really well, the brown wire comes from one of the other filter caps' ground lug and obviously the left lug on the tag strip also funtions as a ground lug

Maybe I should put silicon both under and over it, to reduce vibrations (and reduce the risk of shorting)? Is there a particular type you would recommend, preferably one that can also seal the big one on the PCB? It has to be reversible, in case I ever want to reverse the mod, or that they need to be replaced (in 20 years or so)... Haha!

Just as a sidenote, I was eager to wire it up with DC heaters and started to look into it, but actually it's surprisingly quiet for such a high gain circuit. Especially considering that those lazy tea drinking Brits didn't even twist the filament wires, but I did for the added tube

[Stevem]

If you get a roll of insulating paper from antique electronics you can do as I have done.
Flatten out a section of paper 1/2" larger around then the filter and clear silicone glue it to the chassis, then once dry silicone the filter to that.
It takes a lot of force to remove either one dry!

[pompeiisneaks]

Thanks a lot Phil, much appreciated! So the capacitor itself can touch the chassis, as long as the positive lead doesn't? It's already grounded really well, the brown wire comes from one of the other filter caps' ground lug and obviously the left lug on the tag strip also funtions as a ground lug

Maybe I should put silicon both under and over it, to reduce vibrations (and reduce the risk of shorting)? Is there a particular type you would recommend, preferably one that can also seal the big one on the PCB? It has to be reversible, in case I ever want to reverse the mod, or that they need to be replaced (in 20 years or so)... Haha!

Just as a sidenote, I was eager to wire it up with DC heaters and started to look into it, but actually it's surprisingly quiet for such a high gain circuit. Especially considering that those lazy tea drinking Brits didn't even twist the filament wires, but I did for the added tube

I use GE Silicone II (or they seem to have rebranded it to GE Silicone 2) it's non acid curing so it won't etch pcb's and components.

Yeah DC heaters are rarely as needed as most people think they would be.

~Phil

[alfi27]

I have been thinking a bit about this, and I have a new idea: What if I replace one of the 50+50uf cap can with a 100+100uf, and then get a 16+16uf or 32+32uf and mount it horizontally like mr Suhr have done in this amp? No silicone needed, and easily replacable and reversible if required! The only potential issue I can think of is that the chassis doesn't have a lot of room on each side inside the head cabinet, but the screw(s) for the mounting clamp shouldn't add that much.

Skjermbilde 2019-04-02 kl. 13.00.05.png

[pompeiisneaks]

If you've got room, it will work. It's been done a ton.

I think the usual reason is that two x 50 is cheaper than 1 x 100 but that may not always be the case.

~Phil

[alfi27]

If you've got room, it will work. It's been done a ton.

I think the usual reason is that two x 50 is cheaper than 1 x 100 but that may not always be the case.

~Phil

I just measured, and there is plenty of room. A 2204 JCM800 has so much room that you could probably fit 6 preamp tubes if you wanted to...

I won't replace a 50+50 with a 1x100, but a 100+100 so I can remove the big cap resting on the circuit board. And a 32+32 in a horizontal clamp will replace the one hanging in the air. A little icing on the cake on that one, when the filter caps need replacing I can just swap to the other lug as I will only be using half of it at the time

[pompeiisneaks]

sounds like a win win!

~Phil

[alfi27]

Yeah sure is, can't believe I didn't think of that before I bought them (the 100uf at least). If the Royal Mail is quick I'll get it sorted by the weekend, and I'll post some pics when it's done!