I'm in the process of building my first express using the A1a schematic. The stupid question I have is concerning the EL34 tube wiring. What do you do with the third or unused grid? Lets say the pinout for the grids are
pin5=grid 1 (nearest cathode)
pin 4=grid 2
pin 1=grid 3 (nearest plate)
Here is where I'm at...
pin 1 hooked to 1k resistor then to B+2
pin 5 hooked to 1k5 resistor then to bias resistor
Thanks,
Eric
That's not a dumb question! The screen grid is on pin 4, so that connects to B+2, the control grid is on pin 5 (which you've wired right), and the suppressor grid is on pin 1. Connect a jumper between pin 1 and the cathode at pin 8, ground the two of them together, and you're all set.
Thanks for the correction, that's a very good point you make about tying the suppressor to the bias supply. It does provide better reliability in the EL34, but at the same time it does change the sound a bit, so I guess it's really something a person should try for themselves to see if the difference is a good thing. I sure like the tube life in those old Traynors though!
I find just changing to a slightly darker sounding EL34 counters the little extra brightness you get. I use JJ E34Ls routinely, and these are perfect for wrecks to my ears. I just like the way my screen voltage doesn't go through the floor as the grids go thermonuclear when you hit a big power chord
That's a great idea when using the JJ's! I formed my personal opinion on that particular trick when using the somewhat bright SED's, but I can really see how that might be just the ticket with the darker tubes. I'm really looking forward to trying that out. Thanks!
