Why use the EH toroidal at all?

[ragtime8922]

I assume there's a good reason for it but it doesn't make sense to me as a first time tube builder.
Why go from 120AC wall volts to a 12 volt wall wart to the toroidal to get 120AC again just to get the 160 DC?

Could you just skip the wall wart and the toroidal tranny and just rectify the AC right from the wall if you only need 160VDC?

I understand that you need the filament power but you could just use a voltage divider, right?

Please, no links. I read about a million of them from the last million threads on trannys and power supplys and don't remember anything that directly relates to using only wall AC rectified.

[slajeune]

A power transformer is used to isolate you from the mains (i.e. the 120VAC coming from a plug in your house).  Without doing this, there is a good chance that you will become the link between the mains and the ground which isn't a good thing.  Many older radios didn't use transformers to isolate the mains from the radio.  They are also know as 'death traps'.

You can use a 1:1 ratio transformer (also known as isolating transformers).  Hammond makes interesting transformers (look at the 262 series, they are isolating transformers with a filament out!).

Cheers,
Stephane.

[Ge_Whiz]

That 12V has got to be accurate and stable, or else your filaments will go pop. It also needs to be at comparatively high current, which would be difficult with a voltage divider unless you used big, hot resistors.

By comparison, the needs of the HT supply are much less critical, and it's quicker and easier to do it as shown, rather than buying specialist transformers and so on.

[R.G.]

There's a much more important reason not to do this.

You -- could -- die.

Never, never, never do anything with the AC power line except attach it to the primary of a transformer through appropriate switching, fusing, etc. wiring.

The reason for the transformers is to keep you breathing.

[ragtime8922]

There's a much more important reason not to do this.

You -- could -- die.

Never, never, never do anything with the AC power line except attach it to the primary of a transformer through appropriate switching, fusing, etc. wiring.

The reason for the transformers is to keep you breathing.

One of the main things that concerned me when making the transistion to tubes from 9V FX was the high voltage and AC in general. I always wondered how to NOT get a hot chassis. Years ago I used to fix video poker machines and one time a guy was playing and while pressing buttons on the machine he touched a metal counter and got blasted. He ended up being OK but it scared everyone. I put my meter from the poker machine chassis and the counter and got 110v!!! My boss grounded a wire and that was that.

So, when you isolate your circuit with a transformer you COMPLETELY save yourself from making a hot chassis?

Also, when you hear circuit ground and earth ground are they the same point electrically only referring to keeping the connections to one area(star grounding)?

The reason I asked the first question is that it just seems dangerous to connect anything to the chassis with AC but yet it is considered to be safe.

[puretube]

nevertheless:
http://diystompboxes.com/sboxforum/viewtopic.php?p=200736#200736
http://diystompboxes.com/sboxforum/viewtopic.php?p=200758#200758
:lol:

[object88]

So, when you isolate your circuit with a transformer you COMPLETELY save yourself from making a hot chassis?

No, there are always people finding new and inventive ways of electrocuting themselves.    I bought a slightly broken Ampeg Gemini, which was shocking the player plugged into it.  Someone had added a master volume pot to the rear and then proceeded to smash it in.  The broken pot (with some 300V+ on it) was rattling around inside, making contact with the chassis.  This sent a nice little surprise up to the guitar player via the grounded instrument wire.  It's mostly fixed now.  :lol:

If I understand it correctly, a transformer will burn up and create an open circuit long before the circuit sees that 120V at 20 amps you'd get from the wall socket if it weren't there.  I think that's where the protection element comes into play.  But it has additional benefits, as mentioned before.

Also, when you hear circuit ground and earth ground are they the same point electrically only referring to keeping the connections to one area(star grounding)?

Yes, so far as I understand.

[puretube]

little side-note: it doesn`t need to be E-H or toroidal,
but a (good) transformer should be there!

(a so-called "auto-transformer" won`t do its job, here!!!)

[william]

There was a what I thought was a really good discussion on transformers a while back.  http://www.diystompboxes.com/sboxforum/viewtopic.php?t=19799&start=0&postdays=0&postorder=asc&highlight=death

[zachary vex]

for many years consumer tube-loaded products like phonographs and radios were wired up without isolation transformers.  i used to hate it... i learned as a young child to touch the phonograph in the garage with the back of my hand before changing a record, to see if i had to reverse the plug first.  even with isolation transformers, lots of guitar amps only had 2 prong cords early on, and had those silly ground switches which moved a smallish cap (.01 or .1?) back and forth from one leg of the a.c. to the other to stop buzz... same deal, really.  searching for the ground leg (the neutral is connected to ground back at the fuse box).  

i never heard of anyone dying as a result of those radios and phonographs that had hot chassis.  but they sure were a pain in the ass.

[puretube]

it used to happen in europe, @ 220V...
those "allcurrent" devices (with their "U"-series tubes) were supposed to be designed such, that absolutely no metallic parts were to be touched from the outside;
there always were warnings on them, a.o. not to connect any stuff (e.g.: external loudspeakers) to them...