grid current draw

[JC@]

It would be easier to measure than to ask but I don't have any amp to check right now.
About how much current does a tube (EL34 i.e.) draw from the bias supply?
I have to calculate the power for the bias supply in my 25xEL34 burn-in rig.
Thanks

[Arthur B.]

It would be easier to measure than to ask but I don't have any amp to check right now.
About how much current does a tube (EL34 i.e.) draw from the bias supply?
I have to calculate the power for the bias supply in my 25xEL34 burn-in rig.
Thanks

It depends on you bias voltage.

[JC@]

That leaves me right where I was.
I'll ask it this way: about how much bias current per tube it is needed in any tube amp more or less properly biased?

[carlg]

I didn't know they drew any significant amount of current, but I guess with 25 going at once it might be something measurable. Curious to know the answer to this one.

[nico.verduin]

Based some specs on the web, the max rating is 0.3uA. I would guess that for 25 x EL34's you should have enough on 10mA. I think it is more important to take into account the load from the filter caps and resistor divider.....25 x 400V x 40mA.... wow...Big PT or is it going to be a switching supply?

[JC@]

Based some specs on the web, the max rating is 0.3uA. I would guess that for 25 x EL34's you should have enough on 10mA. I think it is more important to take into account the load from the filter caps and resistor divider.....25 x 400V x 40mA.... wow...Big PT or is it going to be a switching supply?

I thought it was going to be little, but that is tiny. I couldn't find those specs, now I feel more confident.

Trying to simplify things, If I use a small lab adjustable power supply as the negative bias supply, positive to ground negative to the grids, should I take some kind of protection with this, like a diode placed between positive and chassis ground?

I decided not to put audio signal to the tubes, so a switching power supply will be used for the B+ if I find one. If not, I already found a 400/380 to 240/220/117 volts industrial transformer I will use backwards. It's big enough and cheap.

[nico.verduin]

About the PT... Msart idea. Never thought of that one. You could also make a small powersupply by using a cheap transformer, diode couple of caps and a couple of resistors and a simple lin pot (wirewound) for the adj. voltage. A lab would be fine as well as long as then Neg is not connected internally to GND.
Never found a switching supply yet with these voltages yet. If anyone knows one? (sorry for borrowing your thread).
Nico

[JC@]

About the PT... Msart idea. Never thought of that one. You could also make a small powersupply by using a cheap transformer, diode couple of caps and a couple of resistors and a simple lin pot (wirewound) for the adj. voltage. A lab would be fine as well as long as then Neg is not connected internally to GND.
Never found a switching supply yet with these voltages yet. If anyone knows one? (sorry for borrowing your thread).
Nico

The PS I found was 0-80 volts, fine for 6L6 and EL34, but maybe to small for the KT tubes except the KT66, so definetely I'll go for the little home made power supply for the bias.

Thank you very much for pointing me out about the neg to ground internal conection. I tend to forget this kind of things.

About the switching high voltage power supply, no, nor do I. The only ones I find are used huge linears from HP and such, quite expensive, and the shipping cost is outrageous for these...