SE Circuits

[ViperDoc]

I'm looking at SE circuits. I want to build a clean-capable SE circuit with around 15 watts of output. The apparently defunct AX84.com has an interesting amp kit called the SEL that runs SE KT88 out of a Hammond 125ESE OT with multiple primary and secondary impedances, allowing a good variety of output power, but seems more like a Marshall build. Xtian gave me a solid look at this Black Butte amp he did a couple of years ago, which sounds incredible. I found a YouTube video of a guy who built a Dumble sans OD Preamp into an SE KT66 output stage that sounded insanely good, too. As usual, I want to know what I need to know. Are there good resources out there that collect necessary SE info to design one properly? I find mostly articles about the Champ. Thanks.

[Phil_S]

The apparently defunct AX84.com...

I know this isn't your question. This disturbed me (well, not that extreme,) so I went there. There was an announcement from Chris Hurley about SE transformers, a link to the AX84 archive, and a link to the new "Guitar Amp Builders Forum." I see the old AX84 projects are all still there. I think it would have been a big loss.

[echuta13]

I would probably look at a Blackface front-end for it. RJ's Eagle is pretty close to what you might be looking for (I'd add a mid control though). https://ampgarage.com/forum/viewtopic.php?f=6&t=14349

[Colossal]

I've done a PTP KT66 SE build and it was excellent. I plan to build another at some point.

[ViperDoc]

Sweet, thanks for the link, echuta13. Colossal, is there a schematic unicorn prancing in the ether? SE KT66 is where I think I want to go.

The Eagle Supre looks interesting, I wonder if anyone built one with a CLC filter?

[Colossal]

Sweet, thanks for the link, echuta13. Colossal, is there a schematic unicorn prancing in the ether? SE KT66 is where I think I want to go.

The Eagle Supre looks interesting, I wonder if anyone built one with a CLC filter?

I was just going to say...

Start with the Eagle Supre topology and reformat to taste
Definitely C-L-C the ENTIRE AMP

[imjonwain]

I built a P1/p1extreme variation with a single KT88 output tube and a CLC input. It's very quiet and the cleans are really great until the obvious breakup point. I have the preamp biased for a bit more headroom so with single coils it's pretty loud before breakup.

[ViperDoc]

I built a P1/p1extreme variation with a single KT88 output tube and a CLC input. It's very quite and the cleans are really great until the obvious breakup point. I have the preamp biased for a bit more headroom so with single coils it's pretty loud before breakup.

Good to know, thanks.

[statorvane]

There are some really good SE resources on SEwatt.com. Free to register, this was originally an offshoot of the 18watt.com website which was centered around modifications to the Epiphone Valve Jr amplifier. There are two broad sets of forums - SE and Push Pull each with sub forums.

http://www.sewatt.com/forum

[ViperDoc]

Thank you, I’ll definitely check that out.

[ViperDoc]

Regarding the Eagle Supre Schematic here:

Eagle Supre - Schematic - Rev 1.5.jpg

When adding a CLC filter, would you use the same cap values on both sides of the choke, like this:

RJ Eagle Supre CLC Draft.pdf

[pullshocks]

FWIW, here is the link for the AX84 SE KT88 power amp. the 3rd page has a choke option, slightly different than on your draft. I have built the 6V6 version with the choke option and it works great.

https://ax84.com/archive/ax84.com/stati ... ematic.pdf

[ViperDoc]

FWIW, here is the link for the AX84 SE KT88 power amp. the 3rd page has a choke option, slightly different than on your draft. I have built the 6V6 version with the choke option and it works great.

https://ax84.com/archive/ax84.com/stati ... ematic.pdf

Excellent, thank you, pullshocks!

[imjonwain]

In my build I have the full PS current going through the choke (it's under 100mA at idle). If you look at the p1 extreme schematic I replaced the first 100r resistor in the PS with the choke. I used a 100mA 3H Hammond unit. Technically the choke is at and sometimes slightly over (at startup) it's 400V max rating with my PT. I haven't had any issues as of yet.


an Epiphone Electar Tube 10 makes for a fairly cheap build platform too. The OEM PCB is actually very sturdy and has sufficient unused pads to play around.

Here's my build:
https://tfrelectronics.com/TFR-SE-88/

I need to update the site as I changed the V1a & B cathode resistors.

[pullshocks]

Note that in the AX84 schematic, nothing is connected to B+1. As I understand it, the first filter cap (C1) and the 100 ohm resistor (R1) gives an "extra" stage of power supply filtration, to offset the inherent hum of the SE power amp.