Monkeymatic Blackbox

[xtian]

Monkeymatic Blackbox lives!

I turned my Judybox Revival salvage into a low-wattage 2x 6V6, fixed-bias, simplified Princeton style amp, using only misc parts on hand. Sounds great at first fire-up, though when dimed I am seeing FLASHES in one of the power tubes. I've got 470R screen resistors. Higher value? Or bad tube?

I probably need to dump a little more signal with the voltage divider before the PI.

330 volts on the plates, using the 265-0-265 HV taps.

[Leo_Gnardo]

when dimed I am seeing FLASHES in one of the power tubes. I've got 470R screen resistors. Higher value? Or bad tube?

Nice work! That's making lemonade out of a lemon all right.

Got flyback diodes on those plates? That's no guarantee of preventing internal arcing - if a tube's that bad it will arc - but for a buck's worth of 1N4007's and 10 minutes work you'll have done what you can to minimize it.

[Smokebreak]

Yea man! Good work! I recognize that chassis . Heads up I think all of the stock pots are linear taper, mine were.

[xtian]

"Linear taper" - seems OK. Volume won't turn completely off, but taper is good. Bass control works well only from 0 to 3 on the dial, but that's pretty typical of Fender tone stacks.

I put the chassis back in the head, and now it sounds shitty. Lots of buzzes and low frequency rattles, maybe osciallation or ghosting even. I didn't think the cabinet was that bad before...

[gingertube]

Flashes in one output tube with a B+ of only 330V, almost certainly a bad tube. I run 6V6 higher than this in both my guitar and HiFi Amps. The HiFi Amp has 150R screen resistors (Ultralinear connected), the guitar amp has 1K and has a Pentode Mode/Ultralinear Switch which I HOT switch without hastles.
I've seen some older gassy 6V6s do fairly spectacular light shows.
Cheers,
Ian

[xtian]

Installed flyback diodes on plates (but new JJs have solved that problem). Sorted some other stuff, and she's sounding pretty really nice. Not bad for a sub-$200 combo! Ordering a custom faceplate.

[xtian]

This amp was suffering from too-damn-much-bass syndrome. I solved it by replacing the cat bypass caps on V1a with 1u and V1b with 2u2. SO MUCH better. Possibly too far...may have to mess a little more, but we're 95% of the way to perfect.

Got my custom faceplate installed. Now I just have to replace the stupid handle with a how-much-more-black model.

Played it last night at a great venue, the Women's Club in Chico. Generous stage, nice dance hall. Fun! Amp sounded GREAT!

[chopstuck]

That amps looks worlds apart from the original state of mine. You should read the blog from the founder of JBox and see the pictures of the factory they were setting up.
It looked like they were afraid of the tools being stolen so there were like none visible.

Marc

[xtian]

I read http://judyboxamp.blogspot.com, but that's just from a fan, he's not involved with Judybox. Where did you read?

[chopstuck]

It was a few years ago and just looked again but couldn't find it.

It was sort of a travel log by a traveling companion. Had pictures that shows the rusticity of the area. where they were sharing a brew and the IIRC, a dirt floor brick building harkening back to the days of a friends' peace corps stories.

Marc

[xtian]

I have been playing this amp at all my gigs for the past few months. It's been awesome!