PT confusion

[soje]

I'm looking for a PT for a 50W build with juice enough for two el34.

However I'm getting confused. Regarding #124, with a 022756 fender trafo, you have around 440V on the plates. But I've read that you get 1.25 * Vrms after silicon rectification. The mentioned trafo I believe is spec'd 320v - 0 - 320v @ 450mA, so:

1.25 * 320V = 400V

....in the words of pumba: "Hey, but you said errr....."

- How do you end up with 440V on the plates? Is this mesured without a load?
- How many amps (before/after rect.) should the PT be rated for, in order to drive two EL34 into 50W ?

Thanks!
Soje

[benoit]

The multiplier should be 1.414, which would give you about 450V DC, less with an actual load.

[UltraHookedOnPhonix]

I used a Fender Twin (TF130) PT for my 50W EL34. Puts out 457V loaded with 320-0-320 secondaries.

[soje]

So next question is this:

How much current will two EL34 PP draw, with a plate voltage of 440V? I can't figure it out from the datasheet.....maybe I'm just daft

...or in other words, how many amps should the PT be rated for in a 50W EL34 dumble clone (three 12ax7 in the preamp)?

[benoit]

So next question is this:

How much current will two EL34 PP draw, with a plate voltage of 440V? I can't figure it out from the datasheet.....maybe I'm just daft

...or in other words, how many amps should the PT be rated for in a 50W EL34 dumble clone (three 12ax7 in the preamp)?

Are you asking about the 320V secondary or the heaters?

[UltraHookedOnPhonix]

how many amps should the PT be rated for in a 50W EL34 dumble clone (three 12ax7 in the preamp)?

Each EL34 will draw 1.5A and each 12AX7 will draw .3A. Your total draw is going to be somewhere around 3.9A which is well within the maximum current draw of a Twin PT which is 5A I believe. Mine is running very cool!

[UltraHookedOnPhonix]

double

[heisthl]

The multiplier should be 1.414, which would give you about 450V DC, less with an actual load.

Moot point but
1.414 is the multipler for a full wave, for a "summed" half wave add the secondares and multiply by .707 - same number.

[soje]

Doh, forgot to mention

The heaters I have no problem finding from the datasheet. It's the 320V sec. I'm thinking of.

How do I determin the currentdraw of two EL34 in PP with 440V on the plates? I've looked araound, but it can't seem to find an answer. It should be more than just the bias sum for the two tubes right?


Regards
Soje

[heisthl]

read the tube chart for maximum plate currents for all tubes and add them together then for good measure increase it by 20%.

[soje]

I'm really starting to feel silly here, but I can't find a max anode/plate rating on the datasheets.

The cathode however has a max rating of 150mA. Is this what I'm looking for?

[Structo]

Plate current will be annotated as Ia.

Plate voltage is Va.