EH Toroidal and Duncan's PSU designer II/Puretube???

[aron]

Duncan's PSU designer is asking for the following:

V RMS (voltage)
and source resistance.

Alternate, the calculator asks for:

Primary Supply voltage (I suppose 10V)
Winding resistance in ohms ?

Secondary

Off-load voltage V RMS ( I assume 220V?)
Winding resistance in ohms ?

Obviously the turns ratio is 22 (10V in 220V out)

What is the impedance (in ohms) of this EH Toroidal?

Puretube, any ideas???


Here's a question:

If I power the transformer off of a regulated voltage, do I need to do anything after the transformer? (i.e. rectify, filter?)

I'd like to use this for a couple of projects:

One needs 125V DC for a tube.
Other is a tube preamp.

Thanks,

Aron

[puretube]

1: sorry, don`t have access anymore to the precise data;

information lost...

[aron]

Thanks!

I have a question, re: ohm/resistance of the transformer. To measure, do I simply set my meter to ohms and measure the resistance of the primary and then the secondary? Wouldn't it be very close to zero ohms?

[puretube]

information lost...

I tend to not use the expressions "primary" and "secondary" anymore - too misleading in these 2-transformer cases -

[puretube]

btw, Aron: what happened to the "Schematics trading - dist. pro, red Llama, hotcake, tbiac" thread ?:
http://diystompboxes.com/sboxforum/viewtopic.php?p=144380#144380

I didn`t think it was that bad? It suddenly disappeared round june, 22nd.

:?:

[aron]

At the end it did get kind of bad. I received complaints so I got rid of it.

[puretube]

arrgh, I missed the end, while sleeping...

[aron]

Puretube,

Given that 12VAC is input into the transformer, are the heaters powered off of the 12VAC?

[puretube]

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:wink:

[moosapotamus]

I'm thinking of building a two channel Alembic F-2B and powering with one of these toroids.

So, two rectifiers, then?... one on the output of the toroid for the high voltage (prior to filtering), and another in parallel with the toroid to rectify the 12VAC?

How do you go from 12VAC down to the 6.3VAC that's indicated for the heaters in the Alembic?

Thanks!
~ Charlie

[aron]

I believe that if you rectify the 12VAC, into DC, then you can use a standard LM7812???

For 6V, you can try the LM7806 (pretty close) or simply alter the fixed voltage regulator to a variable one.

I think it can handle up to 1 amp w/heat sink.

Or, I think you can ignore the 6.3V requirement and drive the tubes off of 12VDC mode.

[moosapotamus]

The Alembic scheme indicates that the heaters want 6.3VAC, tho... not DC.

http://www.geofex.com/FX_images/alembpre.gif

~ Charlie

[aron]

Charlie, you can feed these tubes AC or DC. DC being quieter. A popular mod for a lot of amps to make them quieter is to feed the heaters DC instead of AC to reduce hum.

There are also 2 modes of running the heaters 12v or 6v, off the top of my head, I can't remember how to wire them, but it's really easy.

As far as tone difference between 12V and 6V, I'm not sure if there's a difference.

[moosapotamus]

Cool, Aron! Guess I need to go do a little reading. I'll go bone up on the DC heater stuff.

If anyone can point me to a good source of info on this, I'd appreciate it!

Thanks, again!
~ Charlie

[R.G.]

The first time I did the back to back transformer setup, I was amazed at how the winding resistances affected things. Specifically,  to Aron,

V RMS (voltage) and source resistance.

That is the net source resistance in the sense of all the way from the power company generator to the output of the winding feeding the low voltage winding you're trying to drive. If we make the sweeping generalization that we can ignore the power company resistance to at least the wall plug, then we only need to know the DC resistance of the wall wart primary and the DC resistance of the wall wart secondary, then refer the primary resistance to the secondary by the square of the turns ratio; that is then the source resistance that the power supply designer is looking for.

If it's a 120Vac to 12Vac wall wart good for 1A, then it's likely that the "12vac" is actually higher than 12Vac unloaded. It's the 120Vac to the unloaded voltage that is the turns ratio. If you want to know what you're going to get, you have to measure the AC wall voltage carefully, then measure the unloaded secondary voltage, then compute the source resistance as Rsource = Rsecondary + ((Vs/Vp)**2)*Rprimary.

If you do that, the standard death-warnings apply to the process of measuring the AC line, and any messing about with the 230Vac coming out of the thing.

To calculate the sag at the output high voltage side, you have to also throw in the driven transformer's resistances as well.

I had  two 120Vac to 12Vac transformers that I could have sworn were big enough, but the output voltage kept sagging badly. Sure enough, when I measured the resistances, I was losing my voltages in the winding resistances of the two transformers in series. It sagged about 45%!

By the way, the sag is much bigger than you'd think from the output current. The pulsed nature of rectification means that (relatively) huge current pulses are pulled through all those winding resistances in series.

I tend to not use the expressions "primary" and "secondary" anymore - too misleading in these 2-transformer cases -

It's important to keep the primary and secondary terms for what they really mean - the primary is the driven/input winding, the secondary is the output winding. This usually means specifying the voltage and maybe a transformer designation as well. The calculation of voltage losses is a major reason to keep which is primary and which is secondary (in the sense I just gave) straight, especially where a fair amount of the output power is siphoned off for filaments in the inner LV:LV windings.

[Lonestarjohnny]

Tone wize, you won't hear a difference, but on the Quitness you will, the DC can be used to drive any 12v or 6v or 5.4 v tube and you don't have to contend with 60 cycle hum that you do with A.C. you can look at this on any scope and see the difference.
JD

[puretube]

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[puretube]

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[Lonestarjohnny]

Puretube, You can run 35 to 40  Postive charged volts through the heater's on any tube as long as you" don't " reference the tube's to Ground and the higher the voltage the cleaner tone you will achieve, this is done a lot now day's for a studio quite amp.
You may have other plan's, if you do forget what I'm saying, no offense takin.  
JD

[puretube]

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