WEM Custom 15

[Diabolical Artificer]

I'm no expert on this Amie but have seen caps across SW's on several bits of gear and various schematics, but it can mean power is on with the power SW in the off position, a cap passes AC right? Therefore I think you have to get the value right or better use a snubber, IE a resistor and cap in series, again I'm no expert. This amp might have a neon indicator meaning if a cap or snubber is used it will stay lit, not ideal.

No idea Rob, I would try what you have, I have several pulled of old PSU's but from memory they are usually something like 47r and 10n, but I reckon for your amp a SW on the 0v tap of the secondary would be better. The tap and chassis ground are right near the mains primary voltage selector, so it's easily done.

Whilst on the subject of adding switches, I added a tremelo SW to mine so the tremelo can be kicked in without a FS. Again easily done without much hacking, having said that a 1/4" jack plug with tip and sleeve connected will do the same job, all your doing is grounding one valves cathode.

Andy.

[Terry]

I mention an X rated capacitor in my previous post but these would need to be Y rated to ensure the equipment didn't become live when switched off in the event of a fault.

Snubbers aren't expressly covered here but you should find the article of interest.

https://www.allaboutcircuits.com/technic...apacitors/

[Mark Hennessy]

Thanks Mark. Yes I understand the snubber across the contacts, but am surprised that just a capacitor is used. If you happen to close the switch at peak mains, it must arc (Shorten the life of the switch), or is it just the best of a bad choice. I have seen those capacitors wired L to N that have puffed out what appears to be stinky steam?

Amie

Yes, while an RC network is best, a single C can work.

Will it shorten the life of the switch?

It depends. How much worse was it with no cap?

Of course, the arc caused be the capacitor depends on how much energy was in the cap, and that depends on luck, basically. While it's possible to get very theoretical about snubbers - and sometimes that's necessary - a lot of them are just plucked out of thin air. But then, rules of thumb are often good enough.

You're thinking of the infamous RIFA X2-rated caps - paper dielectric sealed in a resin case. All fine until the resin cracks and exposes the innards to the atmosphere. Paper, of course, is hygroscopic. There's a lot of moisture in the air!

https://lanas-kenwood-spares.co.uk/wp-co...-BOARD.jpg

The trouble with the smoke from these is the deposits, which can be hard to clean up. I dread to think how bad the fumes must be for us!

The real fun is when those caps are embedded inside those filtered mains inlets:

https://www.vintage-radio.net/forum/show...hp?t=88137

Often with no fuse protection beyond what's in the mains plug, as the equipment fuse is normally downstream of the filtered inlet. And because of the potting compound, the explosions are often more violent. Not good!

[Bushbaby]

I'm certain I have some polyester x1y1 caps in my workshop so I assume I can wire this in series with a resistor (100R 2watt too big??) but I need to know what the values are (I believe they are 275v). Very naive question though here and its because I do not want to blow anything/cause an electric shock - where should I wire them across??

Best Regards

[Diabolical Artificer]

"where should I wire them across??" Good question. the mains SW on mine was DPST, so does that mean two snubbers or just one on the live? That means the SW has four contacts two for live, two for N, the RC goes from contact to contact. Now your going to ask R before C or C before R on the feed? : ) R before C I'd say but Bog knows, try it one way, if that don't work try it tother way. Tack/bodge/attach with flying test leads - them in first to see if it does any good, somehow I doubt it. As I said before the mains SW is a combined SW and pot, wiper to control grid, so any arc or pop is going to be amplified quicker than the HT can drain. A bit like me letting off a banger near your ear.

Way I see it you have several options. 1) try a snubber
2) Fit a "htr" SW
3)Fit another mains SW, leave in present SW/pot as volume control.
4) Fit some sort of timed off/relay combo between amp and speaker, or between EL84 cathodes.
5) Flog the amp and buy a new hat/handbag/toolbox for the missus.

Andy.

[Terry]

RC or CR shouldn't make any difference, Andy!

In any case, with AC mains, how do you know 'which way up it is' at the instant you operate the switch?

[Kalee20]

Catching up on this thread... Try 10 ohms in series with 0.1uF 'X' rated capacitor.

Thanks Mark. Yes I understand the snubber across the contacts, but am surprised that just a capacitor is used. If you happen to close the switch at peak mains, it must arc (Shorten the life of the switch), or is it just the best of a bad choice. I have seen those capacitors wired L to N that have puffed out what appears to be stinky steam?

Amie

It's a good point. Connecting a capacitor across the contacts will fix impulse noise when they open (the voltage rise is controlled) at the expense of trouble when they close (current impulse can be huge). Gives the contacts a hammering.

It also means the capacitor is seeing mains all the time the equipment is switched off (but still connected). Having experienced the dreaded Rifa capacitors as Mark says, only suggestion to Bush Baby is to switch off at the wall after you've switched off at the switch.

It all seems a lot of trouble just to remove switch clicks!

[Terry]

Catching up on this thread... Try 10 ohms in series with 0.1uF 'X' rated capacitor ...

... It also means the capacitor is seeing mains all the time the equipment is switched off (but still connected). Having experienced the dreaded Rifa capacitors as Mark says, only suggestion to Bush Baby is to switch off at the wall after you've switched off at the switch.

Not if Y rated caps are fitted instead of X rated!

Please see my previous comments in post #42 and don't forget to follow the link!

[Bushbaby]

Hi All
Seasons Greetings to you.
Sorry I've not been online recently but I've been very busy work wise.
I've had a look through the caps I have and found these - any thoughts?

           

[ppppenguin]

The first 2 are 100n X rated. The last is 1n (103 means 1 followed by 3 zeros) X and Y rated. All are OK across the mains. The 1n part is also OK for mains to earth.