Monkeymatic S'express 15-watt

[johnnyreece]

Just gotta chime in and say, love the name.

[xtian]

Revised layout attached. Fixed a couple of errors and added grounding scheme and external bias test points.

[xtian]

Populated board.

[xtian]

Assembled chassis.

[johnnyreece]

Nice noval sockets! Green light, yellow light, red light, STOP!

[xtian]

Yellow means GO!

Finished wiring. Gonna take my own advice and breathe so fresh air, check over the wiring carefully, then apply POWER.

[xtian]

Looked it over, found two wires I hadn't run yet. Passed bulb limiter test. Powered up with tubes, voltages look good, except way to much -bias voltage. No sound, obviously.

[xtian]

Works. Better than works. IS AMAZING. Zero hum. Huge, HUGE sound. Thank God I put in the PPIMV master. Won't have an opportunity to play loud until late tomorrow. But, WOW, simply awesome at bedroom volume.

400v on plates. The Bright switch and tone stack is great. As spec'd in TW Express schematic. Very nice. More to come.

[rdjones]

Works. Better than works. IS AMAZING. Zero hum. Huge, HUGE sound. Thank God I put in the PPIMV master. Won't have an opportunity to play loud until late tomorrow. But, WOW, simply awesome at bedroom volume.

Success, Kudos !

400v on plates. The Bright switch and tone stack is great. As spec'd in TW Express schematic. Very nice. More to come.

400 ? Those poor skinny tubes.
Oh, you might consider swapping the power inlet line (hot) from the ring to the tip of the fuse holder for SAFETY.

rd

[cbass]

Great job nice layout.I may have ta build me one

[johnnyreece]

Great job nice layout.I may have ta build me one

For sure! Excellent work!

[xtian]

you might consider swapping the power inlet line (hot) from the ring to the tip of the fuse holder

Easily done. Thanks, rd. But please explain the rationale?

EDIT: I see now. One can accidentally touch the ring with your finger from the outside of the chassis when the fuse cap is removed. Smart.

[martin manning]

It's more than that. If you are inserting the fuse into the holder with your fingers you are poking in there with what is essentially a bare wire. Best practice is to first insert the fuse into the cap and then put the assembly in. You could still accidentally be touching the metal holder in the cap, so the hot lead should not be connected to the ring. By the time the fuse is inserted far enough to contact the center terminal, there is little chance that your fingers could be touching it.

[Bob S]

And don't ask how we know this...

[xtian]

Yes, I've been zapped on a fuse holder. Not even my build!


Last night I measured 22 watts clean power (biased at 60%!). I'm using an OT spec'd for 15 watts. I'm afraid I'm going to burn it up if I crank the amp. Wasn't expecting this much fire breathing, but then, this is my first Express style build.

What is the implication of pushing a 4 ohm load instead of 8 as designed? The OT has 8k5 primary/8r secondary. I'll get lower output wattage (fine), but am I in danger of higher flyback voltages, or other dangers?