18Watt.com

“That’s not 18 Watts.”
Uhh, but it is …err, eighteen Watts?
Two days ago I became obsessed with ECL86 tubes - the ones used in the Marshall model 1930 Popular. So over the weekend I focused on nothing but this new design. It’s a 2-tube, single ended, class A, 18 Watt amp to be built in a 5F1 chassis in a tweed 1x10 combo with a Celestion G10 Gold speaker. I’ve spec’d it with MM iron but it can be built with Heyboer, Edcor, Hammond or whatever. My new little “Turbochamp”. Now, finding the time to actually build it…

Sounds pretty cool

Looking through the RCA tube manual, it appears that this will be around 8 or 9 Watts output power, not 18 Watts. I was mistakenly originally referring to the plate dissipation rather than the power output.

ECL86s have a hifi cachet so are a bit pricy. I have used PCL86s which have 13v heaters which I ran at 12v for convenience. They cost a third as much a few years ago.
Dd

Update, the schem & layout I posted are missing a filter cap, here are the updated dox and some pix of the circuit on a stock 5F1 eyeletboard.

It’s fitting nicely into a stock 5F1 chassis, with just a few slight mods.

Here's how to build it using EL84s and a 12AX7,
sorry about the low-rez images:

crgfrench wrote: ↑

Fri 11/04/22 8:12 pm

Here's how to build it using EL84s and a 12AX7,
sorry about the low-rez images:
Screen Shot 2022-11-04 at 9.09.10 PM.pngScreen Shot 2022-11-04 at 9.08.47 PM.png

@crgfrench

I might have interest in building the el84 version, as I've been wanted to do a parallel single-ended amp, and like el84's. Do you have a file that is clearer? A bit hard to see on my computer the exact values.

Is there a range of acceptable OT primary impedance? Looks like you used 3k - how low or high can I go? Looks like maybe MM or Edcor are the main suppliers of SE OT's with those specs?

And for PT looks like you used roughly 250-0-250 for a solid state rectifier - what sort of spec to use with a 6ca4? Regular 18w 290-0-290 PT?

Have you built a version using a pentode preamp (ef86 or 5879)? I like the sound of those tubes. Or one using two preamp tubes? I have an ef86 Lite 2p 18w that I enjoy, and that pre into your power amp with necessary adjustments sounds fun...

Maybe this layout is clearer? For the EL84 version

Clearer EL84 Schematic