How many tubes from EH Toroidal Transformer!

[Frankgb]

Hi,

I'm hoping someone can tell me how many 12ax7 tubes I'll be able to power with one of these.

I would like to use it to build a Matchless Hotbox, which has two 12ax7s.

cheers

Frank

[the_random_hero]

What is the output voltage and current rating?

[snoof]

 it depends on how you wire the heaters of each x7.  6v or 12v.  One way it's 300-ish ma, and the other is 150ish ma for each tube. Can't remember which is which.  check the data sheets for the x7's, it'll tell all.

[CraigR]

The main current draw from any tube is from the filament.  The way you wire the EH transformer is with a 12VAC adaptor powering both the primary of the transformer and in parallel, the filaments of the tubes.

The plates of the tubes are the only loads present on the transformer secondary.  Although I have not seen a rating for the transformer, I think you should expect it to be somewhere in the neighborhood of 2 x the usual plate current draw of the two 12A_7's typically used in the EH tube pedals - maybe 200ma or so assuming 50ma per tube..

I would extrapolate from that that you could probably drive up to 3 12A_7's as long as you used a wall wart capable of handling 3 x 300ma for the filaments, plus an additional ~150ma for the plates, times a safety factor of 2, ideally ~2 amps.

Does that make sense to you?

Craig

[Johan]

for a 12ax7, each heater pulls about 1watt ( but that is before the EH-tx, right? )and each funktion ( amplifier, cathodefollower) about 1-2watts to be happy..not knowing the specs. for the EH transformer, we are only talking about 4-8 watts..I would be surpriced if it cant handle that...
j

[puretube]

OUCH !

[bancika]

and each funktion ( amplifier, cathodefollower) about 1-2watts to be happy..

one 12AX7 triode draws about 1mA for the plates, with ~150V at the plates it's only 0.15W.

[aron]

Check out this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=23209.0

[the_random_hero]

it depends on how you wire the heaters of each x7.  6v or 12v.  One way it's 300-ish ma, and the other is 150ish ma for each tube. Can't remember which is which.  check the data sheets for the x7's, it'll tell all.

Basic math - double the voltage, halve the current drawn. The difference is if you connect power to pins 4 and 5 and connecting pin 9 to ground (running the heaters in parallel requires 6.3VAC/VDC and will draw 300ma. Running them in series involves you connecting pin 4 to power and pin 5 to ground (running the heaters in series requires 12.6VAC/VSC and will draw 150mA)