Questions about odd markings on British schematic

[BoomTexan]

I've been fixing a heavily modded Sound City 160 that was blowing fuses. The previous owner wired the neutral to the 3A mains fuse and it was feeding into the transformer. I put it on the variac and got it to about 5V before the variac was shaking violently. Removing the neutral from the fuse holder solved that, but looking at the schematic I'm not sure where the neutral lead is supposed to go.

What is this C marking? Surely I'm not supposed to attach neutral to the center tap, right?

These British wiring designations have been throwing me for a loop for the longest time.

 

[Jasonpatrick]

L is line or live, E is earth and so I’m assuming C is Common? Which is the white wire? Which on fenders I usually hard wire to the transformer then run the black hot or L wire to the fuse base.. I ain’t no pro. Just my guess looking at the schematic .

 

[Pete Farrington]

Do you mean the symbol for the neon pilot light?

Edit - ahh the common end of the winding.
It’s one end of the winding, not a centre tap.
Neutral and C go to either side of one of the poles of the mains switch.

 

[David Barnett]

... I’m assuming C is Common? ...

Bingo!

 

[dan40]

Amps were once wired with the nuetral wire to the fuse first and then on to the switch. Modern code dictates that the hot or "line" wire be connected to the fuse first. Electrically, this is the safer method but the amp will work fine either way. The fact that your variac was "shaking violently" is odd and shouldn't be caused by the neutral wire being wired to the fuse.

 

[robt57]

I first thought it was whitworth. [nudge/wink]

 

[Lowerleftcoast]

I can only imagine how much this beast weighs. It might create it's own gravitational force.

Remember the difference in fuse rating when it is powered with 120v. The Sound City 150 schematic states 3A (5A USA). The schematic you provided doesn't show that.

 

[BoomTexan]

Both

Amps were once wired with the nuetral wire to the fuse first and then on to the switch. Modern code dictates that the hot or "line" wire be connected to the fuse first. Electrically, this is the safer method but the amp will work fine either way. The fact that your variac was "shaking violently" is odd and shouldn't be caused by the neutral wire being wired to the fuse.

Both the neutral and hot were wired together onto one of the lugs of fuse.

Do you mean the symbol for the neon pilot light?

Edit - ahh the common end of the winding.
It’s one end of the winding, not a centre tap.
Neutral and C go to either side of one of the poles of the mains switch.

So what you're saying is that it should already be wired up?
The neon pilot light is kinda also throwing me off. Am I supposed to wire it to the 245V tap and neutral? I've never heard of one of these pilot lights being powered by such a high voltage.

Also, wait, do I hardwire the neutral to the 245V tap? That's wild, never seen that before.

 

[Lowerleftcoast]

Both the neutral and hot were wired together onto one of the lugs of fuse.

That is shorting hot and neutral. Yikes. No wonder the Variac had trouble.

The neon pilot light is kinda also throwing me off. Am I supposed to wire it to the 245V tap and neutral? I've never heard of one of these pilot lights being powered by such a high voltage.

Sure. A 240v lamp can be powered by 240 volts. It can light with USA voltages as well.

do I hardwire the neutral to the 245V tap? That's wild, never seen that before.

The 240v primary coil has taps for the lower voltages.
Neutral will terminate with the *C* end of the coil. (If wired to UK specs, it should terminate at the *Mains On/Off* switch, before heading to the *C* end of the coil. Just like the schematic shows).
Hot will go through the fuse, then *Mains On/Off* switch and then terminate at the voltage selector switch.

 

[David Barnett]

I can only imagine how much this beast weighs. It might create it's own gravitational force.

Remember the difference in fuse rating when it is powered with 120v. The Sound City 150 schematic states 3A (5A USA). The schematic you provided doesn't show that.

And being a Sound City amp, it's probably got Partridge transformers. It may not be as heavy as an SVT, but I bet it's not a fun thing to lift.

 

[Jon Snell]

It is just poorly centred capacitor over the polarity death cap.
For 110volt non grounded mains only. Not considered 'safe' elsewhere so not used!

 

[Bob Womack]

From the folks who gave us Lucas Electrics for cars, creator of the three position switch - "Dim, Flicker and Off." Who else wires everything positive ground and insists it is the only proper way?

Bob

 

[BoomTexan]

And being a Sound City amp, it's probably got Partridge transformers. It may not be as heavy as an SVT, but I bet it's not a fun thing to lift.

Actually, mine is a 1974 model, they stopped using the Partridges in 72-73 iirc, which is rather unfortunate. They're still MASSIVE though. I think it's close to 60lbs without tubes. I do actually have a SVT right now as well, and it's far heavier, but the Sound City isn't easy to move.

It is just poorly centred capacitor over the polarity death cap.
For 110volt non grounded mains only. Not considered 'safe' elsewhere so not used!

Yeah, I took the ground switch out of the circuit, which shouldn't be an issue at all, just put ground to the chassis and that should be good, right? I've been having so many problems with this amp, it was modded a while ago, and not done well, and there's so many issues with it that are just absolutely ridiculous. I'm having to redo parts of the amp that look very concerning that I later discover were fine to begin with, and parts of the power supply that I deem too easy to be screwed up at any point have been SEVERELY screwed up.

 

[Pete Farrington]

Am I supposed to wire it to the 245V tap and neutral? I've never heard of one of these pilot lights being powered by such a high voltage.

That’s kinda what we’re stuck with over here. We make do, where there’s a will there’s a way
Whatever, by the magic of transformer action, provided that the intended voltage is connected to the intended primary tap, 245V will appear at the 245V point shown on the schematic. Hence a neon intended for 245V will get the correct voltage.