Increase the Current Draw of Power Tubes?

[Boots Deville]

Dan Boul of 65 Amps fame has a weekly steaming internet show on UStream every Wednesday.

Yesterday he was talking about their new amp "The Producer".
http://www.65amps.com/the-producer.html

On the website it goes on about how the amp runs EL34s in an "extremely safe and unconventional way that no off the shelf guitar amp transformer can do."

On yesterday's show he elaborates a bit and indicates that it has to do with running the tubes at a lower voltage and higher current.  The following is quoted from yesterday's show:

"Tubes hate voltage and love current.
The less voltage you can put on the tubes, the longer they're gonna last.
A lot of amps drop the voltage level but if you don't change the current swing, the current value of the transformer, it doesn't sound good at all.
With "The Producer", with Mercury Magnetics we've created a power transformer that throws out a lot of current.  It draws more current than a 100W Marshall."

Any idea what's going on here?  How you might get two EL34's to draw in the neighborhood of 280mA like four of 'em do in a 100W Marshall?

[firemedic]

Really low plate voltage. I imagine there would be very little headroom.

[Willabe]

I think that's backwards.

Tubes can take the extra voltage, amp makers have been running them over voltage for decades.

But the more current you run thru them the faster they were out.

Seems to me this is well known and accepted.   


               Brad     

[Boots Deville]

@Brad, his point is that new tubes can't take those over-voltage designs (from the website).  I have heard him say elsewhere that the JJ 6V6 can handle 475 on the plates as long as the screens are kept low.  I think he's saying if you run more current thru them *at a lower voltage*,they don't wear out (as fast).  But how exactly is that accomplished?

@Firemedic - this amp also has what they call a "Master Voltage" which is a form of power scaling, so it can be reduced even further.  I've heard him say that they scale the whole amp, not just the power amp.

[Willabe]

@Brad, his point is that new tubes can't take those over-voltage designs. I think he's saying if you run more current thru them *at a lower voltage*,they don't wear out (as fast).  But how exactly is that accomplished?

I don't think it is.

While it maybe so, that new tubes can't take the over voltage of older designs, that still doesn't mean they can take any more current draw (even at lower plate voltages) and not wear out as fast.

I doubt any new manufacture tube has as good of a cathode as when tubes were in their hay-day. Better materials, including the coating on the cathode and harder vacuum led to a longer life over all. I'm not sure that new tube manufacturers even know what companies like Telefunken and RCA were coating their cathodes with as far as chemistry.

A cathode can only give up so many electrons in their (use full) life time. It's like a battery, it can only give up so many electrons and then, no more to give.

The more current you demand from either of these, the faster you drain them to the point that they have no more to give.

I could be wrong, but from what I've read over the years this is accepted as true.

PRR and HBP could tell us much more about this, hopefully they chime in on this.


                      Brad        

[Colas LeGrippa]

i don't know much about that, but if I want a power tube tube to draw more current, I raise the plate voltage, Can a tube draw lots o current if the plate voltage is so low ? Second, I prefer the tone of an EL34 with 350V on the plate and let's say 65mA that 250V on the plate with 100mA. that's for sure.

[tubeswell]

It not about the voltage or the current singularly, its about both of them together (which equals the power handling).

It you have a lower plate voltage, then you can increase the current to get the same relative power handling. And vice versa. However, with a lower voltage, the amplification of the tube will be less than it would be with a higher voltage, unless you increase the current and increase the load.

[Willabe]

I think he's saying if you run more current thru them *at a lower voltage*,they don't wear out (as fast).

Tubeswell this is what i was refering to.  ^

If you lower the plate voltage __and raise the current draw__ how do you extend the life of a tube? I don't see it.    


                        Brad