EL84 SE BIAS

[TIMBO]

Hi guys, Building a SE El84 clone of a much sort after little amp http://el34world.com/Forum/index.php?topic=19477.msg201773#msg201773
Using what I have on hand transformer wise I have come up with this.

I originally did not have a valve rectifier.
With the SS rectifier I was hoping my voltages were close to this.

Knowing that I'm not going to be able to get the voltages close to the original amp I've increased the cathode resistor to 390ohms.
As per the voltage chart the EL84 is at about 90% plate dissipation (just under 11W).
With the valve rect in the plate dissipation is lower as expected.


Should I increase the cathode resistor to 470 ohms just to relieve a bit of stress???

Also I'm thinking that a DPDT switch to add in a 100ohm resistor in series to the 390ohm would work when in SS rect mode.

[shooter]

I'd say ship it.  you using modern tubes?  I did a PSE el84 at about 11w a tube and to my knowledge she's still out in the world making music

[TIMBO]

Hey shooter, Just did the calcs on the original amp
Plate-264v
Screen-266v
Cathode-7.3v
Plate-cathode 256v
Plate diss-12.7w

[labb]

It is pretty common to bias single end amps at 90% dissipation. I think that if you look at some of the old Fenders you will find some at 100%. I have built several SE amps and all are at 90%. Not a problem.

[EKDENTON]

I have the el84's biased hot in my Orange amp with a 120 ohm resistor.  I have not had any problems at all. It sounds awesome and I use that amp a lot. I tried a larger value resistor and the amp did not sound very good. Of coarse this one is PP and your doing a single ended but I just wanted to say i am using the JJ brand tubes and they must be pretty stout, the data sheet suggests 270 ohms for pp class ab.

[TIMBO]

Thanks guys, A good day in the shed and I think this one is sorted.



On to the fun bit...........the cab 

[TIMBO]

Hi guys, CAB is done!!

[shooter]

very fine as always!, I like how you stacked one on the other, so the bottom amp is next

[TIMBO]

Hey shooter, WHICH one do you want me to do next 

[TIMBO]

What about one of these.............

[shooter]

 
Son, you win
you need to go play in the desert for awhile!

[TIMBO]

Hey shooter, A mate did a clip for me.
https://www.youtube.com/watch?v=V3FmZ2_1ppE

[shooter]

sounds great! although I do lean pretty hard SE, PSE, QSE

[super&plexi]

Dug the tube rect. Clips....its got more breath, like a songwriting amp. Cool as hell. And loved your presentation