Power Supply for 4 x EL84's in PPP

[kleuck]

Obviously, an 290v/300 mA PT and a 2*290/300mA are two different animals, and do not have the same output power.
It like comparing the color of apples with the taste of pears, if you plan to build a 36 watts amp, you need a 80 to 100 watts PT, center-tapped and non-tapped obviously exhibiting different voltages and currents, but identical powers.
If you suppose from the beginning the same current for a tapped and a non-tapped PT, obviously you are describing from the beginning two PT with different power ratings, so the comparison is weird imo, or am i missing something ?

[krx]

Obviously, an 290v/300 mA PT and a 2*290/300mA are two different animals

That is exactly the point you were missing in the Hammond design guide where they are measuring voltage across the WHOLE winding (look at the diagrams) irregardless of whether it has a center tap or not.

A 290-0-290 is 580V, a 0-290 is 290V. If you want to get 408V out of the 0-290, you will need to use a bridge rectifier and you will not get the specified current but rather 0.62 multiplied by the specified current. If you want 408V out of the 290-0-290, you can use a full-wave and get the specified current. You could also use a bridge rectifier to get a whopping 818V out of it, but you'd only get 0.62 times the original current.

This is pretty basic stuff here.

[krx]

Okay. So you wanna build a 36W? You need 4 EL84s. They're going to run with the plates around 340 and dissipation around 12W. That means the plate current is going to be about 40mA max (it could be less if you bias colder, of course, but we're talking about an 18 which is usually biased very hot). Add in some extra current for screens and preamps, and you really should have at least 200mA current available from your power supply. That's the minimum I would use, though I'd feel better with 250mA.

Let's assume you have a cap input power supply and are using silicon rectifiers. You can either use a full-wave bridge or a full-wave. If you use a full-wave, easy, you want 275-0-275 @ 200mA. If you use a bridge, you will only get 0.62 times the current stated in your PT specs. That means you need a PT that will put out at least 200mA/0.62 = 325mA with 275V across the primary.

The original post specified a 310mA PT @ 280V, which I think is cutting it close unless you KNOW your PT is overbuilt or you aren't planning on running the amp hard.

[guitarmike2107]

Not that he needs it but KRX is right.

IMHO There is no need to use a centre tapped transformer unless you plan to use a valve rectifier or would like the option to do so.
So most of my trannies that I have made up for diode rectification are set up for bridge rectification, they generally tend to work out slightly cheaper this way and there is no significant draw backs. But you have to heed what KRX is saying about specifying the current properly.

Also I think it has been said that 36watter prefer slightly lower voltages than 18watter and its good to have some factor of safety built in … so saying that

So I would go with a 0-260v @ 350mA secondary.

Your filament current spec is borderline… 3.8A to 4A would be better … ……

[kleuck]

This is pretty basic stuff here.

Hehe, even basic stuff can be misunderstood in a foreign and technical language.
You are right, but it's not rational to me to compare PT this way, the right way would be to compare PT with the same power ratings, and see what current and voltage are in each case rather than comparing different pieces of winding in the same spreadsheet.
That's why the Hammond PDF looks strange to me.

[radstringz]

No one has addressed the problem with the heater circuit in EDL's original post.

It's a good idea to reference ground through 2 x 100 ohm resistors; I'm pretty sure that directly grounding one leg of the heater line is a recipe for disaster.

jr

[breakfastbuddy]

its the same power output , no matter how its rectified , were is the pages that you find that answer that the current nearly lose half the current ?
62% , the current goes down to 70% and the voltage goes up .
if you can use the whole voltage , if you can not you lose more .
and what do you mean is the relation of tube power vs that 12watt power ?
i know its a good idea to have the PT bigger than you need , but its good to know were the theoretical values are .
sorry about my bad english .

[kleuck]

No one has addressed the problem with the heater circuit in EDL's original post.

It's a good idea to reference ground through 2 x 100 ohm resistors; I'm pretty sure that directly grounding one leg of the heater line is a recipe for disaster.

jr

Hoops, indeed !

[breakfastbuddy]

and its 200 ma .
http://www.ampmaker.com/275-0-275v-36w- ... 254-0.html
so i dont think your info is correct

http://www.ampmaker.com/275-0-275v-36w- ... 254-0.html

[guitarmike2107]

The info is correct, I suggest you go research the difference between full wave rectifiers and bridge rectifiers and transformers.

That 275-0-275 transformer could also be described as a centre tapped 550v.

So if we choose to use the centre tap and full wave rectifier, after rectification you only have ~388v @ 200mA say.

If we did not use the centre tap (i.e. no connection) and used a bridge rectifier we would get ~770v @ 124mA.

it all depends on how you look at a transfomer and what type of rectification you use...

[chabby]

Obviously, an 290v/300 mA PT and a 2*290/300mA are two different animals

That is exactly the point you were missing in the Hammond design guide where they are measuring voltage across the WHOLE winding (look at the diagrams) irregardless of whether it has a center tap or not.

A 290-0-290 is 580V, a 0-290 is 290V. If you want to get 408V out of the 0-290, you will need to use a bridge rectifier and you will not get the specified current but rather 0.62 multiplied by the specified current. If you want 408V out of the 290-0-290, you can use a full-wave and get the specified current. You could also use a bridge rectifier to get a whopping 818V out of it, but you'd only get 0.62 times the original current.

This is pretty basic stuff here.

Just as an FYI - There is no such word as "irregardless" as the term regardless already means without regard to. Irregardless would then mean: without, without regard to. think for a minute....what does regardless mean? It means without regard to. Now think of it's opposite....with regard to. You can't not attribute meaning to something twice in the same thought, because you're voicing a single idea.
Anyway, I just have to point this out because I know if it were me, I'd want to know. Because I used to use that term too, until I realized what was up.

So the term for "irregardless"is simply regardless.

Therefore using a made up term "irregardless"is like saying regardless twice. It's a common misnomer and misinformed use of the english language.The only reason I point it out, is because my ex-girlfriend used to say it and wouldn't change her mind, even after I explained that to her and referenced the dictionary. Her trailor park roots were too deep and the poot wasn't good enough to overlook it.