EL34 Pin out?

[mike_mccue]

Hi,
I am trying to relearn some basics about the EL34. I'm starting a D.I.Y. project based on the EL34... I'm working with the AX84 P1eX design.

I recall the EL34 has a pin out that uses pin 1 for the screen.

I am trying to understand the details of why it's OK to place a tube like a 6L6 (with proper bias adjustment) in a tube socket that has been wired to work with a EL34.

This was explained to me once many years ago... but it only became pertinent now that I am trying this DIY project.

Is it simply the case that the EL34 is a true Pentode while the Beam Tetrode design simply doesn't have the extra screen?

Thanks very much,
mike

[Gtr_tech]

Pin 4 is the screen, pin 1 is the suppressor grid. The 34 is a std pentode and thats why there's a seperate connection to the suppressor. Beam tubes operate on a slightly different principal and don't require a suppressor grid to have a linear response. That suppressor must be tied either to gnd or the bias supply to do its job and thats why pins 1 and 8 are tied together in amps that use the EL34.

Think of it this way: Electrons are emitted from the cathode, "allowed" past the control grid via the voltage on it. Next in the path is the screen, which acts as an accelerator....sort of boosting the momentum of the electrons so they can reach the plate without getting lost along the way. If this happens (screen failure), the electrons just "hang around" in a cloud (space charge) and don't reach the plate. Next in line to the plate....the suppressor. When the screen whips electrons at the plate, the velocity can be so high that a portion can bounce off and get lost. The suppressor's job is to reflect them back to the plate. This improves effeciency and smooths out the response curve. Early on pentodes were called "Kinkless tetrodes" due to the new design that eliminated the kink in the characteristic curves.

[mike_mccue]

Thanks,
I apologize for being so casual with the term screen and using it rather than suppressor grid.

best regards,
mike

[mike_mccue]

I need to ask a simplistic question... to help eliminate any ambiguity in understanding.

Is it correct to think the no Beam Tetrode has a Suppressor Grid?

Thanks.

mike

[Gtr_tech]

Not a grid, no. The beam forming plates take the place of the suppressor grid in beam tubes.
http://www.radiomuseum.org/forumdata...way_Spbg57.png

[mike_mccue]

Thanks.

best regards,
mike