Question about wiring a multi-section can capacitor

[BoomTexan]

I'm thinking about buying a double-section 100uF + 100uF 500V can capacitor for my Selmer TNB 100SV, but I've never actually dealt with these multi-section can caps before. How should I wire it up for the capacitors to be in series, like in the schematic below? Is it even possible?

Would it just make more sense to get eight 220uF caps at 250 or 300V and wire them in series to reach 110uF at acceptable voltages, then in series again like in the schematic? Or maybe like 4 multi-section 50uF+50uF 500V caps in parallel?

 

[Phrygian77]

What did they use in the amp? How much room do you have?

I don't know why you're considering anything other than 100uF unless you're wanting more filtering. Also, I don't understand where your getting 8 from. You're not going to need more than two in series.

I'd use four F&T 100uF 450V caps, a pair in series for the main filter, and a pair in series for the screen filter, exactly like they are on the schematic. If you want more filtering for the input filter, use F&T 220uF 300V for the first pair.

 

[dsutton24]

Depends on the cap construction. Usually those multi section caps use the case as a common lead for the caps. Wiring those caps in series would be impossible.

 

[Phrygian77]

I haven't seen multi section caps that don't have a common negative. Save me the trouble of looking through your other threads on this amp, and post the pictures here of the filtering arrangement.

 

[BoomTexan]

The bottom 4 are the 100uF filters.

They're single section cans, and they're wired pretty straightforwardly. The issue is that I can't find any 100uF 500V cans for less than $25 apiece, and I'm not paying that kind of money.

The issue with getting the F&T 450V is that the transformer output is right at 460V. If I were to order a 25 or 50V one and wire them in series, it'd half the capacitance. I guess I could order some Zener diodes and drop that by 16-32 or so, but that's kinda cutting it close and losing 30 volts or more across all components is bound to cause a lot of tone change.

I got 8 because I'd need to double the voltage coming from the 220uF caps, so wiring in series is necessary. I'd get 110uF for 2 of those in series, reasonably close there, and 600V for voltage, which is well over any surge voltage. I need to replace all 4 can caps, they're each about 50% out of spec and I just don't want to risk it. Thats where I got 8 caps from.

I guess this info puts an end to the 100uF+100uF idea, but I could apparently still use the 50uF+50uF at 500V can caps or the dual 220uF in series.

 

[schmee]

Some multi section are isolated so the case is not ground. These have a tab for ground. Ran into this capping an old Sansui Stereo recently. It had 5 cap cans and two IIRC were isolated.

 

[Phrygian77]

The issue with getting the F&T 450V is that the transformer output is right at 460V. If I were to order a 25 or 50V one and wire them in series, it'd half the capacitance. I guess I could order some Zener diodes and drop that by 16-32 or so, but that's kinda cutting it close and losing 30 volts or more across all components is bound to cause a lot of tone change.

I got 8 because I'd need to double the voltage coming from the 220uF caps, so wiring in series is necessary. I'd get 110uF for 2 of those in series, reasonably close there, and 600V for voltage, which is well over any surge voltage. I need to replace all 4 can caps, they're each about 50% out of spec and I just don't want to risk it. Thats where I got 8 caps from.

I guess this info puts an end to the 100uF+100uF idea, but I could apparently still use the 50uF+50uF at 500V can caps or the dual 220uF in series.

I'm sorry, but you're not making any sense. I'm not following your logic.

If you replace the 100uF cans, exactly how they are wired now, with F&T 100uF 450V caps (one for each can!), how is that not sufficient? It's way more than enough voltage capacity.

 

[BoomTexan]

I'm sorry, but you're not making any sense. I'm not following your logic.

If you replace the 100uF cans, exactly how they are wired now, with F&T 100uF 450V caps (one for each can!), how is that not sufficient? It's way more than enough voltage capacity.

The output from the transformer is 460V when it first hits the caps. I don't want to have the voltage 10V higher than the caps are rated for.

 

[Phrygian77]

Check the diameter of those cans. If they'll fit, the JJ 50+50uF cans are $10 each. So, for what you'd pay for a good high voltage 100uF (unless it's Illinois Capacitor) plus a terminal strip and the trouble of all that, you could just use those JJ cans ... again, if the existing cans are 1.375" diameter. You'd wire the two positive terminals together to make them 100uF caps. Then, each pair is wired in series, exactly like they are in the amp now.

 

[Phrygian77]

The output from the transformer is 460V when it first hits the caps. I don't want to have the voltage 10V higher than the caps are rated for.

They're in series. They're already in series in the amp as it is. You basically get one 50uF 900V cap out of two 450V 100uF caps.

 

[Phrygian77]

Let me put it this way. Look at the schematic. Look at the amp. There are two filters. Each filter consists of two 100uF caps in series plus balancing resistors. Two 100uF caps in series makes a single 50uF filter with twice the voltage rating of the individual 100uF caps. The whole reason they used two caps in series for each filter was to double the voltage rating of the filter.

 

[BoomTexan]

They're in series. They're already in series in the amp as it is. You basically get one 50uF 900V cap out of two 450V 100uF caps.

I'm so sorry to waste your time like this explaining this to me. I have no idea how I didn't see that, it was right in front of my eyes the whole time, I'm so embarrassed.

Thanks for helping me on this, I'm trying to keep the dumb questions to a minimum, but I've only been at this for 4 months now and a vintage 100W tube amp is a pretty difficult piece of work for someone of my limited expertise.

 

[Phrygian77]

I'm so sorry to waste your time like this explaining this to me. I have no idea how I didn't see that, it was right in front of my eyes the whole time, I'm so embarrassed.

Thanks for helping me on this, I'm trying to keep the dumb questions to a minimum, but I've only been at this for 4 months now and a vintage 100W tube amp is a pretty difficult piece of work for someone of my limited expertise.

I'll all good. You were scaring me talking about 8 caps. I just want to encourage you not to do something like this, which I found in a 1962 6G2 Princeton.

One of those 100uF 50V caps would have been perfectly fine.