‘Correct’ power switch / fuse wiring

[StrummersOfThunder]

The advice on the internet is all over the place with this

Fuse before switch makes sense inc see you have a shorted switch issue

SPST vs DPST ?

I’m aware modern commercial guidelines call for breaking both the hot and neutral but I see SPST calling switches are still the mainstay of home built vintage style tube amps.

Should I bin the SPST and go the DPST route or can I continue on my merry way ?

[jeremyb]

I think you'll find a standard kiwi wall socket is only single pole so its probably not a big deal

[Cdog]

Pretty sure DPST is the ISO standard. Definitely safer than SPST if you plug into a transposed power circuit.
SPST is from the days when amps had death caps an no earth pin

[NippleWrestler]

IMG_20241110_104142.jpg (568.76 KiB) Viewed 1342 times

Speaking of no earth pin, this is what I discovered today in my new (to me) Mesa. I tried it at the guys house, it sounded huge, drove it home, plugged it in, turned it on to a massive pop, a brilliant flash of light from the power tubes and some smoke from one of them.

The fuse, grid resistors, filter caps we're all fine so I didn't know wtf was going on, then saw that when I was about to call it a day.

I replaced it with a big yellow bastard that actually allows for some flex in the power socket and now all is well, apart from the fright taking a few months off my life.

IMG_20241110_105131.jpg (419.87 KiB) Viewed 1342 times

Aren't guitar amps fun?

[jeremyb]

JINKIES!!!!

[StrummersOfThunder]

Yikes

[NippleWrestler]

JINKIES!!!!

That's similar to what I said.

I'm somewhat surprised I didn't hook myself up to the mains by flipping the (metal) standby switch, but I guess somebody thought of that which is nice. It would be a bit shit if people's lives were held in the balance of a skinny brittle wire.

[TmcB]

This is why people shouldn’t buy mesas….

[robthemac]

This is why people shouldn’t buy mesas….

Oh you just want them all to yourself.

[TmcB]

This is why people shouldn’t buy mesas….

Oh you just want them all to yourself.

Mesas sound great but if you follow any of the amp tech channels they loathe them for just doing absurd crap like this

I wouldn’t say no to a lone star special even knowing that though….

[robthemac]

This is why people shouldn’t buy mesas….

Oh you just want them all to yourself.

Mesas sound great but if you follow any of the amp tech channels they loathe them for just doing absurd crap like this

I wouldn’t say no to a lone star special even knowing that though….

Yeah I play and hope. Have owned three. Still own one. thankfully haven't needed any work outside of warranty period.

[NippleWrestler]

Here's the thing. I've owned and worked on about 10. I'm not an amp tech yet I can fix them by looking at a schematic and deducing what's wrong. If I can do and I'm half-retarded then what are these guys doing? To me it's a bit of a fallacy that they're hard to work on, as since they're all through hole components you can see the parts and do most of the work topside. The bits are right there, and it gets tight, sure it does, but an amp with 2 channels, 4 modes, recording bits, tube or diode rectification, and whatever else isn't going to be point to point unless it was the size of a fridge. And then people would complain it's the size of a fridge.

In this particular instance, I've not seen this in my other amps, and I can tell someone else has been in here. But then again, the amp is 30+ years old so I'm not surprised it may have been dicked with. Was that little wire stock? Maybe. Maybe not. It did come loose when I drove it home though and that's not good, but now it's fixed so job done I suppose?

So forget YouTube techs. Trust your own experience. Mine tells me it's no different to work on a Mesa than anything else, in most cases they're easier than Marshall, Peavey, Engl, Etc of the same era because, as mentioned, everything is right there and the wired pots are a great boom over the board mounted ones a lot of companies use.

On the other hand, if someone is set in their ways and opinions I'm not going to change them, nor would I expect to or even care to, that's not really my thing. I've just been inside a ton of mesa amps from up to 40 years ago and not really encountered something I couldn't fix myself, which is pretty good for a guy who just reads a schematic and owns a soldering iron.

Anyway. As you were.

[TmcB]

The mesa thing is more that they under spec many components for the voltage going across them (e.g. all the orange drops) and do bonkers stuff like giant heat sinks that are just bolted to the chassis with nothing remotely nearby that needs heat sinking.

When I saw the crucial earth wire to chassis being a paper clip I thought that was in keeping with their odd mentality.

I do hear you on the pots being accessible though, PCB mounted pots are incredibly frustrating when all the need is a shot of cleaner to fix but they’re buried under a mountain of stuff. Don’t get me started on Fender reissue boards….

[sizzlingbadger]

Several Youtube "Techs" like to pick on certain brands, not really sure why or what they want to achieve.

Surge voltages are quite normal in power-on situations.

Capacitor surge voltage is standardized in IEC/EN 60384-1. For aluminum electrolytic capacitors with a rated voltage of up to 315 V, the surge voltage is 1.15 times the rated voltage, and for capacitors with a rated voltage exceeding 315 V, the surge voltage is 1.10 times the rated voltage.

The surge voltage is the maximum voltage which may be applied to the capacitor for short periods of time, i.e. up to 5 times for 1 minute each per hour. Surge voltage testing is conducted according to IEC 60384-4.

So as long as the capacitors are good quality and have a proper surge rating they will be fine. Which is why there are 1000's of Mesa amps out there without issues.

All manufacturers build to a price, and that all do that in their own way, it's easy to pick on them when you don't have to answer to the financial burdens of running a company in the 21st century. That aside some do some questionable shit sometimes.

[TmcB]

Several Youtube "Techs" like to pick on certain brands, not really sure why or what they want to achieve.

Surge voltages are quite normal in power-on situations.

Capacitor surge voltage is standardized in IEC/EN 60384-1. For aluminum electrolytic capacitors with a rated voltage of up to 315 V, the surge voltage is 1.15 times the rated voltage, and for capacitors with a rated voltage exceeding 315 V, the surge voltage is 1.10 times the rated voltage.

The surge voltage is the maximum voltage which may be applied to the capacitor for short periods of time, i.e. up to 5 times for 1 minute each per hour. Surge voltage testing is conducted according to IEC 60384-4.

So as long as the capacitors are good quality and have a proper surge rating they will be fine. Which is why there are 1000's of Mesa amps out there without issues.

All manufacturers build to a price, and that all do that in their own way, it's easy to pick on them when you don't have to answer to the financial burdens of running a company in the 21st century. That aside some do some questionable shit sometimes.

To be fair though, it’s not the cheap cheerful stuff getting picked on, it’s the multi thousand dollar amps that are being built with corners cut. Shrinkflation at its best

Sure, they might be rated to handle a surge but surely it’s better to buy the part that can handle the surge in its stated range when it’s probably 2c more? They’re not thinking consumer here.

I get the tech’s complaints - amps aren’t being built for them to easily work on/service AND the consumer is paying high price for cost cutting. That’s what they’re going after.

They can still do it right if they want - one look at your Astoria will tell you that. When your PCB (not good pcb) Deluxe Reverb is barely shy of $5k and you could get a Tone King imperial for comparable gold, there’s something broken. Not saying Tone King is amazing, more that assembly line stuff is now getting into boutique price range.

Maybe I just like hearing people grizzle.