Fixed Bias El84?

[JKRamsey1991]

So I’m thinking of my next build and I am leaning towards a fixed bias El84 amp with a Trainwreck preamp (my current favorite). Anyone have any information on a fixed bias el84 power section? What’s the ideal plate voltage on a duet of el84s? And can anyone recommend a PT for me to save me hours of research?

[sluckey]

Look at this...

     http://sluckeyamps.com/vox/Vox.pdf

[SILVERGUN]

The Mesa Studio .22 caliber was a fixed bias 2- el84 amp that you can borrow from.

Hoffman sells an 18 watt transformer that would work great, but it currently shows as "out of stock"

In the meantime, if you're ok with a SS rectifier, this ain't a bad option:
http://www.classictone.net/NOS17375.pdf

[JKRamsey1991]

Look at this...

     http://sluckeyamps.com/vox/Vox.pdf

I don’t see a bias tap on that transformer. I would have to scheme up another way to get the negative bias voltage

[sluckey]

I don’t see a bias tap on that transformer. I would have to scheme up another way to get the negative bias voltage

Don't need a bias tap.

[JKRamsey1991]

[/quote]Don't need a bias tap.
[/quote]

How would you suggest getting the negative bias voltage? I want to use a more fender style power amp with the el84s

[SILVERGUN]

Look at this...

     http://sluckeyamps.com/vox/Vox.pdf

[tubeswell]

How would you suggest getting the negative bias voltage? I want to use a more fender style power amp with the el84s

Copy the Princeton reverb bias supply typology - runs straight off one side of the High Tension winding with a 100k AC dropping resistor, then the bias diode etc

[Garrett335]

Look at this...

     http://sluckeyamps.com/vox/Vox.pdf

Quick side question Sluckey, I was looking over the schematic and layout that you linked, I don't understand on the power section layout page it appears as if there are (2) 8pin tubes one says V6 5y3 (rectifier) and the other says Pre-amp connector, what is the pre-amp connector? I've never seen this before.
(Sorry for side tracking the post)

[sluckey]

The preamp is on a separate chassis. The preamp connector supplies filament and B+ voltage and signal between the two chassis. Like this...

[sluckey]

How would you suggest getting the negative bias voltage? I want to use a more fender style power amp with the el84s

You could start by looking at the schematic. Bias voltage is derived just like a Fender Princeton Reverb, or many Marshall amps.

[Garrett335]

@Sluckey

OHHHH, haha, I fully understand now, thank you for clarifying that for me.

[JKRamsey1991]

@sluckey

My apologies not exactly sure how I missed that. I’m blaming not enough coffee but stupidity is much more likely!

[92Volts]

Are you using fixed bias to copy the sound of a particular EL84 amp? If so, copy that amp.

EL84s aren't used with fixed bias often because they need less bias voltage... the effects of cathode biasing are reduced.

The most accurate way to scale down an EL34 design is probably to set up EL84s identically (fixed bias) so you may have good reason for this. But cathode bias has worked well in a range of amps from Voxes to the Marshall 18W.

[JKRamsey1991]

Just want to build something lower wattage than the 35-60 watt amps I have built. Going to be in a Princeton sized combo amp.

[plumcrazyfx]

You can also look at the Traynor YGM-3 or 4 or the Bassmate.  They are fixed bias EL84s.