Replacement Caps

[bobloblaws]

Hello there,
So I have this vintage Canadian amp here, no schematic, and I'm replacing a number of caps that have drifted way high in terms of capacitance measurement. Photos below. I'm not sure what to replace these with. For starters, both the red ones and the gray ones have power ratings of 600 WV. I assume WV means "watt-volt". For my purposes can I just read that as 600 V?

The gray ones appear to be electrolytic but have a relatively low capacitance (.05uF) and no clear indication of polarity, unless the silver on one end indicates negative and the black on the other end indicates positive. I usually order caps from Digikey and the lowest value electrolytic I can even search for is 0.1uF. They are between mains power (on/off switch, fuse) and chassis ground.

The red ones have even lower values (.005uF to .25uF) and have a black stripe on one end to indicate polarity. But does that mean they are necessarily electrolytic? Here I run into the same problem of being unsure whether it's even possible to source electrolytic caps with such low values.

Can anyone advise on suitable replacements?

[mozz]

Mouser should have those, maybe .05 is called 50 nanofarads 50nf. WV should be working voltage.

[Enzo]

Yes, WV - working voltage.

The gray ones are not electrolytics. Note they are connected between ground and the incoming 120vAC. They are mains rated film caps.

The red ones are also film caps and have no polarity. The black stripe indicates "outer foil". Outer foil really doesn;t matter to you, though I am sure we can start an argument over that.

0.05uf is 50nf, but Mouser will be happy using 0.05uf.

0.1uf is a common standard value. 0.05 is a rather dated value. There are still 0.05 in the catalog, but you will find more hits using 0.047, which is a standard value.

[bobloblaws]

Yes, WV - working voltage.

The gray ones are not electrolytics. Note they are connected between ground and the incoming 120vAC. They are mains rated film caps.

The red ones are also film caps and have no polarity. The black stripe indicates "outer foil". Outer foil really doesn;t matter to you, though I am sure we can start an argument over that.

0.05uf is 50nf, but Mouser will be happy using 0.05uf.

0.1uf is a common standard value. 0.05 is a rather dated value. There are still 0.05 in the catalog, but you will find more hits using 0.047, which is a standard value.

Ok, thanks Mozz and Enzo, that helps a lot to know that they are not actually polarized electrolytic caps. I thought they might be because the gray ones kind of look like electrolytics and the red ones SEEMED to have a polarity marking, I wasn't aware of the "outer foil" previously. Also the fact that all of them measured quite high, I thought that might be an indication of dried out electrolytics. Good to know for now and future reference. Thanks for clarifying the meaning of "WV" as well.

[Mick Bailey]

Older caps do measure high and they had pretty slack tolerances from new. Any cap attached to the mains is worth replacing with a modern (safer) class cap. Signal and other non-electrolytic caps I leave alone unless they're leaking DC or show outward signs of deterioration.

[g1]

If the caps are going to mains, they should likely be removed with a 3-prong AC conversion anyway.
I'm hoping this is not a 'widow maker' type amp. What is the tube complement?

[Jazz P Bass]

"both the red ones and the gray ones "

The grey capacitors should be removed.
One clearly goes to the mains fuse holder & the other appears to go to a 'polarity reversal' switch.

Need a better pic of the red caps.

[bobloblaws]

Older caps do measure high and they had pretty slack tolerances from new. Signal and other non-electrolytic caps I leave alone unless they're leaking DC or show outward signs of deterioration.

When I say high, I mean quite high. For example the one going from the fuse to ground is labeled .05uF and measures .5uF. There are 4 of those red caps in the amp and measure as follows:

1. spec: .25uF act: 1 uF
2. spec: .033uF act: .09uF
3. spec: .1uF act: .68uF
4. spec: .005 act: .037uF

You wouldn't change caps measuring that far out spec as a matter of course?

Any cap attached to the mains is worth replacing with a modern (safer) class cap.

So a modern cap is safer by virtue of modern safety standards or do I need to look for specific safety ratings?

[bobloblaws]

If the caps are going to mains, they should likely be removed with a 3-prong AC conversion anyway.
I'm hoping this is not a 'widow maker' type amp. What is the tube complement?

Yes, I am planning to install a 3 prong cord. So those two caps are not needed? what was their original purpose? Not a widow maker, it has a power transformer. Tubes are 5Y3, 6AT6, 12AU7, 12AX7, 2 x 6BQ5 (EL84).

[bobloblaws]

... the other appears to go to a 'polarity reversal' switch.

For what it's worth, it goes to the on/off switch.

[Mick Bailey]

The caps intended for mains use are Class X (line-to-line) and Class Y (line-to-ground). Most modern power supplies use them for EMI/RFI filtering and switching noise suppression. In one sense 'death caps' secretly made a comeback with SMPS supplies, though those classification of caps fail safe. Even some recent non-SMPS amps have a filter section comprising one or more common-mode inductors and a number of safety-rated noise suppression caps. More common perhaps in consumer audio gear where immunity from noise is as important as reducing noise fed back into the mains.

I always remove death caps and install a 3-prong lead. Here in the UK they had no functional use and usually were not installed at manufacture, but I see plenty of imported US gear that still has them in place. Where there are other suppression caps (across switch contacts, for example) I replace these with a Class X cap.

Otherwise, as far as cap values go, unless the value has particular significance I leave it alone. There are very few places in a tube amp where the cap value has any impact. Otherwise I'd be doing wholesale cap replacements in almost every 50-odd year old amp that comes my way. Particularly some AC30s where not a single component reads anywhere near what it's supposed to be.

[Enzo]

Are you measuring these caps while they are still wired into the circuit? That will sure alter readings.

ANything is possible, but I have a hard time believing a film cap has gone up to seven times its original value.

[bobloblaws]

Are you measuring these caps while they are still wired into the circuit? That will sure alter readings.

ANything is possible, but I have a hard time believing a film cap has gone up to seven times its original value.

Out of circuit.

[bobloblaws]

The caps intended for mains use are Class X (line-to-line) and Class Y (line-to-ground). Most modern power supplies use them for EMI/RFI filtering and switching noise suppression. In one sense 'death caps' secretly made a comeback with SMPS supplies, though those classification of caps fail safe. Even some recent non-SMPS amps have a filter section comprising one or more common-mode inductors and a number of safety-rated noise suppression caps. More common perhaps in consumer audio gear where immunity from noise is as important as reducing noise fed back into the mains.

I always remove death caps and install a 3-prong lead. Here in the UK they had no functional use and usually were not installed at manufacture, but I see plenty of imported US gear that still has them in place. Where there are other suppression caps (across switch contacts, for example) I replace these with a Class X cap.

OK, so if I understand you correctly I can just remove those two caps (and I SHOULD remove them anyway since they are death caps) because grounding the mains will (more or less) eliminate noise that the caps were installed to suppress.

[Mick Bailey]

The original death cap was intended to provide an AC chassis ground reference for a mains plug that could be inserted either way round. It was usually wired to a switch that would flip one end of the cap to either leg of the mains. Some amps had them hard wired and if the amp buzzed you unplugged it from the wall and inserted the plug the other way round.

If the cap was referencing the live side of the supply and shorted out, the chassis would be live. In any case if a death cap leaks you can get a floating voltage on the chassis. Even if it doesn't leak, there will still be a residual voltage because of the reactance at 60hz.

With a 3-prong supply these are redundant, and in any case not a good idea nowadays. I'd remove them.