deluxe reverb 6v6 plate current ?

[danger-russ]

I think I'm missing something here.
So looking at the data sheet for the jj6v6s
420v to the plate
6.6k ot
420v ÷ 3.3k = 127ma. Class a
420v ÷ 1.65 k= 254ma Class b
When I plot the class b load line on the chart 254ma is off the chart.
Even the class a 127ma seems to be more than the pt can supply.

Not sure what I'm doing wrong here?

[stratele52]

Plate current calculation is to use tube lower than max watt , 14 watts with your plate voltage.

If your amp work in Class A  , around 90 %   at 400 volts plate = 27 ma each tube.

That why you always need to do bias , if not, tube can go up to 127 ma like you write and burn.

[danger-russ]

Seems I had an idiot moment.  I've drawn out a bunch of load lines for pre amps, this was my first for power tubes.
The chart came out completly different,  I thought I was doing domething wrong. Turns out I had the load lines right.
Just wasn't thinking in terms of a push pull amp. The chart shows the valve working either above Pa max or at  cut off.
Just looked wrong to me. Of course with two tubes working together in push pull it's right.

[PRR]

> 254ma is off the chart. Even the class a 127ma...

You are using the Triode curves. Surely you plan to run Pentode?

The usual 6V6 pentode plots only go up to 250V on G2. Available current will rise at higher G2 voltage.

However 250mA is huge even with full 425V on G2.

Frankly this amp is over-Volted. Yes, I know they sometimes run this way sweetly for decades. I suspect because speaker impedance is generally higher than nominal, also the current-clipping against impedance dips is musically useful.

> more than the pt can supply.

In a hi-fi Sine test, the average current will be 0.707 times peak, so it isn't as bad as you may think.

In OVER_driven guitar, it may hover near square-wave much of the time.

> class a

In Class A your peak current can not be more than twice the idle current. At 420V in a 14W plate the idle can't be over 33mA. So 66mA peak, at say 380V peak swing, is over 11K per plate, 22K plate to plate, and only 380V*0.066A/2= 12 Watts RMS output (same as you could get with more reasonable 250V-300V 8K-10K operation).

The peak current does NOT depend on bias class A or class B. In class B the bias is zero current. In class A the bias must be (nearly) half the peak current. And any way I slice it, 420V even 380V 9with tube drop) into 8K or 6K comes over 200mA. 6V6 will almost-barely do 200mA and low plate-drop with 400V on G2.

[danger-russ]

The only graph they have in the jj6v6s data sheet is for triode.
The jj6v6s is supposedly a cross of a 6v6 and 6l6 and can handle 500v, don't know if i belive that.
It will be pentode.
I'm considering dropping the b+ plus down or running an 8 ohm speaker into the 4ohm tap.
The graph looks a lot better with a 13.2k ot.

[jazbo8]

It is strange why only triode curves are available for the JJ 6V6S, wouldn't most people want to run it in pentode mode?

Jaz

[tubeswell]

Bias the JJ at 18-22mA in that amp and they should sound fine