need help reading tube charts

[dragonbat13]

Does anybody know of a source that can tell me what all the specifications on a tube chart mean. I have been searching for something that will tell me what the different numbers mean according to the letters they are labled with but to no avail. Thanks for any help

[LeftyStrat]

Some general guidelines first:

- V is obviously voltage
- I is current
- a means anode or plates
- g refers to the grid
- g2 refers to screens (grid 2)
- P is power (output or dissipation)
- Z is impedance

So lets look at the data for an EL34

http://tdsl.duncanamps.com/show.php?des=EL34

The first section is ratings

Vh - Heater voltage.
Ih - Heater current draw.
VaMax - Maximum plate voltage
Vg2Max - Max screen voltage
VhkMax - Cathode to heater potential, max
PaMax - Plate dissipation
Pg2Max - Screen dissipation

If we're designing an amp, let's say 2xEL34, and 3x12ax7, then we know we need a PT with a 6.3VAC (Vh) winding with enough current handling capability for 2 times 1.6 (Ih) plus 3 times .3 (heater current for a 12ax7).

PaMax helps us when biasing the amp, because in class A/B we don't want to exceed 70 percent of this value.

Now let's look at the next section. Say we're shooting for around 50 watts. Looking at the Pout column (power output) I see an entry for 55. Va is 400, so I would need a PT that would put this much voltage on the plates. Zout is 3,400, meaning I would need an OT that had a 3.4k primary. THD (Total Harmonic Distortion) would be 5 percent. Vg1 is -38. This is the theoretical grid bias.

Does this answer your questions? Maybe others can chime in and correct any errors, I'm still on my first cup of coffee.

[dragonbat13]

That explains everything I need to know the way I needed it explained. To the point. Thanks I am going to print this for reference.

[mhuss]

Nice summary, Lefty!

--mark

[LeftyStrat]

I made a few edits "we're" instead of "were" and I originally had 2x12ax7 but then calculated 3x12ax7 on the heater current.