EL84 power amp with fixed bias - does it exist?

[NSB_Chris]

For my next build, I was thinking about going EL84 on the power amp.  It seems most "modern" lower wattage tube amps I see these days are built on an EL84 platform.  Maybe because they allow for a compact construction, power amp distortion characteristics ...

My original thought was fixed bias with SS rectification. Sort of like a low wattage Marshall.  I built a version Rob Robinette's RR800V, which is a JCM800 preamp with a 6V6 power section that was great.  I thought, why not try something similar with an EL84!  I thought I could find an AC15 schematic or a forum original, but I am coming up blank.  In my research, I am finding only single ended or push-pull with cathode bias.  Is there some reason for that that I am missing?

Any insight, knowledge, advice would be greatly appreciated! 

[sluckey]

Here's one...

     http://sluckeyamps.com/november/november.htm

[NSB_Chris]

That is really great, Thanks!
Did you ever try the hammond PT?

I found references to the ax84 site, but it looked like it was defunct.  They had a note saying something like "click here for our forum in its former glory".  Spelunking through it now to see if I can find some of the schematics that inspired your amp.

[NSB_Chris]

I think I may have found one of the references:
LoWatt by Bryan James

OT:
The print out is difficult to read but it looks like the output transformer is Hammond 1650F.  Hammond lists this as a 25W  7.6K c.t. OT - they don't list the EL84 among the suggested tube types.
The Hammond 1650E might be a good choice also.  15W 8K c.t.   
Thoughts?

PT:
They have a Hammond 270FX, which looks like a 550V PT with ample 5V and 6.3V current capacity.  With a SS rectifier, is 550 too much for the EL84.  It looks from the data sheets that the EL84 is not as forgiving on the B+ voltage level.  Should this be lower output voltage?

[sluckey]

I used a 270FX and 1650F in my second November amp.

[NSB_Chris]

What B+ voltage did you get on the second November amp?  The data sheet for JJ EL34 says the max plate voltage is 300V, which I assume is reasonably typical for the tube type.

Now that I look at the LowWatt schematic, they put a 330 ohm resistor before the B+ tap!

[sluckey]

Voltages are on the schematic at the bottom of this page...

     http://sluckeyamps.com/vox/vox.htm

[tubeswell]

Traynor YBA-2B is another one

[NSB_Chris]

Thanks Sluckey!  So the voltages on both the November project examples are essentially the same.

Thanks Tubeswell for another example!  This one even has a higher B+ voltage.

So all of these have EL84 plate voltages that are higher than the max listed for the EL84.  Is the data sheet that conservative for the max voltage, or am I missing something?

Sluckey, the split chassis design is very interesting.  I am currently building a split chassis design.  Covid-19 has slowed the process because I have limited access to my shop.  That is why I am thinking beyond it to the next project :-)
The motivation for this one is to have the head close to the pedal board with short 4 cable method runs and knobs close for tweaking, but have the speaker wherever it needs to be.

[Bantam]

Very interesting build. Love to see more. Is the tube running between filter can and O.T. between preamp tubes, and also right hand side wall for wire runs?  I was kicking around the idea of the basic nice preamp sound and then different sized output power in separate form.

[tubenit]

https://el34world.com/charts/Schematics/files/Carvin/Carvin_vintage16.pdf

fixed bias and 380v on the EL84

[DummyLoad]

fender blues jr.

--pete

[Johntb]

This is what I used for my ENGL Fireball clone.

https://www.gapcb.com/documents/SuperLite-II-2.7-Schematic-v3.pdf

[sluckey]

This is what I used for my ENGL Fireball clone.

https://www.gapcb.com/documents/SuperLite-II-2.7-Schematic-v3.pdf

But this is a cathode biased amp.

[Johntb]

This is what I used for my ENGL Fireball clone.

https://www.gapcb.com/documents/SuperLite-II-2.7-Schematic-v3.pdf

But this is a cathode biased amp.

Oops! Sorry.

Thats because I'm stupid and wasn't paying attention. 

[frank57]

Hiwatt used a fixed bias on their lead 20, 30 and custom 20 tube amps.Also Jet city amps and their Soldano clones like the 22h.