WEM Custom 15

[Diabolical Artificer]

Pends how you look at it Terry, if the amp has two Mullard EL84's (wot cost and arm and a leg) and a tfmr prone to over heating I would say it's prudent to run at less power OP to give said components an easier life, but under normal circumstances 15w is fine. Nice story BTW.

Andy.

[Bushbaby]

Thank for your replies.
Sticking here rather than the post on transformer wax, I left the amp on for 25 minutes on about 1/4 volume (no input) and switched off. The output transformer wasn't hot at all to be honest, very lukewarm indeed. One thing I have noted though is a loud pop through the speaker when switching off. I hate amps that do this - how do I rectify this?

Many thanks

Rob

[Diabolical Artificer]

Sounds like your mains tfmr is ok Rob, just getting hot when it's cranked up full whack. " One thing I have noted though is a loud pop through the speaker when switching off. I hate amps that do this - how do I rectify this?" Mine did this too, am pretty sure it's the on/off SW, though could be wrong. A cap or snubber across the SW might help. Failing that you could retrofit a sw that cuts the "0v" tap of the secondary, switch this off first, then the main off SW.

Andy.

[Amie]

Just a. capacitor would make the switch arc at turn on wouldn't it Andy?

Thanks,
Amie.

[Terry]

Just a. capacitor would make the switch arc at turn on wouldn't it Andy?

Called EMI/RFI suppression capacitors, they are commonly used to suppress interference caused by any arcing, Amie.

Before switching on a vintage radio or TV for the first time it is common practice to snip out the capacitor across the mains switch (old ones have a habit of going short circuit!) and, ideally, replacing with a modern X rated component.

[Amie]

Between live and neutral though, that's normal isn't it, not actually across individual swich contacts????

[Mark Hennessy]

Perhaps surprising, but yes, it's done. Usually with a low value resistor in series with the cap. More here: https://en.wikipedia.org/wiki/Snubber

Often you can see a spark across switch or relay contacts when they open up - that certainly demonstrates the value of a snubber. You can buy caps with the resistor built in:: https://www.globalsources.com/gsol/I/Snu...971042.htm

The cap between live and neutral is intended to shunt interference between live and neutral, and might well be usefully doing that all the time the item runs. But the RC snubber is only about suppressing switching noise.

[Amie]

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

[Terry]

I have seen those capacitors wired L to N that have puffed out what appears to be stinky steam?

Also known as the magic smoke! (Although they are more likely to go dead short.)

Apologies for mis-reading Andy's post and thanks to Mark for clarifying the situation.

[Bushbaby]

Hi
What snubber value do you recommend??

Best regards