Judybox amps

[xtian]

The Princeton Reverb tone stack is the one that sounds like Fender to me.

http://music-electronics-forum.com/atta ... _schem.gif

[Smokebreak]

I'm thinking Bluesmaster, as another option, and put the midboost on a pullpot https://tubeamparchive.com/files/bm_dcl ... 12_171.pdf

[matt h]

(deleted)

[Smokebreak]

I took the cut out earlier ands its cap's board space is now NFB. I put in the BM stack and this thing is stone cold rockin! Lots o mids, I just fixed it at 10K. Maybe too much bass, I may increase the 47K slope.

[deiseldave]

I'm thinking about turning a Judy Box that I bought into a D'Lite 6V6 kind of thing. Can someone point me to the most fool proof scheme/layout? Thanks.

[Smokebreak]

I'm thinking about turning a Judy Box that I bought into a D'Lite 6V6 kind of thing. Can someone point me to the most fool proof scheme/layout? Thanks.

Here's several https://tubeamparchive.com/viewtopic.ph ... e+versions
These are the ones I referenced for a 6L6 d'lite but you can tweak for 6V6.

[deiseldave]

Thanks.

[Smokebreak]

I had some refreshments last nite, and in my liquid inspired infinite wisdom, apparently I decided I didn't like the amp anymore and started tearing up the board
I must've "dreamt" on it, because I woke up this morning and my first thought was that a JCM800 pre is like a Rocket, with an extra stage...kinda. I had apparently already converted the unused triode to a cathode follower.

So now I have the same switching, and have 3 "channels" :

1. Simple clean channel : 1K5/1u stage feeding tone stack. It was important to get this coupler right so this channel sounded good, then tweaked the rest, as every channel sees this coupler.

2. Tweaked Rocket : I've got AB763 PI and NFB, which I'll put on a switch for Rocket mode. I may also increase the first 100K plate load, as I think the other channels would be fine with that.

3. JCM800 : 470p peaker over 470K feeding 500K pot, no peaker on voltage divider after 2nd stage. I was planning on repositioning the Rocket's 500p coupler so the JCM channel wouldn't see it, but it sounds fine as drawn.
The JCM channel sees 2 gain pots, but the second one (Rocket's 500p, 500K pot) somehow works out great. The effective value of the coupler there is actually around 400p, so it's rolling off around 800Hz, basically right at the mid dip and below. I think. This is working well because the bluesmaster stack seems very bass and mid heavy.

I've got a normal master after the treble pot, and though it's not wired as a rheostat, it somewhat serves the purpose of the 220K to ground that the top boost circuit had, I believe, and close to what I've seen as the PIG control, though it's really just a master volume.

I'm gonna put the cut control back in on the back panel, as cranked, The Rocket could use a little treble cut, especially once I put the NFB on a switch, imagine. I'll use a pushpull pot as the JCM doesn't need it.

All in all I am extremely happy with this amp now. The Rocket is doing the voxxy thing, even with NFB, and I'm over the moon about the JCM800.
I never would've guessed that the combination of 310V plates, cathode biased 6V6s, odd divider with no peaker, 500K pots, 2K2 Rk 3rd stage, 56K Rk CF, Fender PI/NFB, Dumble tone stack, parallel dropping string, no choke, all preamp stages off of one 20K/20u filter , and GZ34 would get me right where I want it for medium/high gain stuff. See, it really is a Hot Dog!
It's warm yet crisp and clear, super crunchy, squishy, and I finally know what "chewy" means now. Very, very fun to play.

[Smokebreak]

I'm just about done tinkering with this amp, and trying to get it all together for tonight's gig. i don't have much time left to test, so I'm wondering...

How big of NFB resistance do I need to simulate "no NFB"?

I was just going to put the NFB on an on/off switch, for the Rocket channel, but thought it would be nice to make it variable for the JCM800 channel.
I can put in a 1M pot, but with my 820r FB resistor and 100ohm tail, I imagine I'll only get use out of a fraction of rotation before it's way too wild on the JCM channel, then it would have to be all the way up for the Rocket channel, to simulate no NFB.

My other option is to use a 5K switched pot, but I'm a little concerned about all the current throw that little switch on the back of the pot.

Or I guess I could use a rotary and just pick 3 or 5 fixed values

Thoughts?

[soberskipper]

Judybox amps were made in Austin until 2007, when, I understand, they flamed out. The amps and components have been showing up since then; a couple of members here have mentioned using their chassis and transformers, combo cabs, etc.

I just bought a Revival 12" combo with speaker, chassis, transformers, pots and hardware--no circuit board, no caps, no tubes--for $99 plus shipping on eBay. The seller has a couple more for sale (and has promised to post more soon). I'll give you my impressions of the component quality when it arrives, but I'd love to hear from anyone here about their experiences.

Not my photo:

[img:640:480]http://1.bp.blogspot.com/-tn4vNfXmRVI/T ... CN4216.JPG[/img]

To my knowledge the amps were always assembled in china. I bought 2 chassis from that guy with transformers and some raped guts. The chassis were a decent thickness but the plating was cheap. The transformers were pretty bad, but i managed to build a decent express for $20 total cost. I will say though that the items were damaged in transit an that guy, the owner who was selling the items on a forum, was super nice about it and refunded me fully. Great customer service - cheap chinese product.

Just my 2c on the original topic.

[xtian]

I recently finished mine, and got to play it at a show last night. Very happy! See my build log:

https://tubeamparchive.com/viewtopic.php?t=25628

[chopstuck]

About 5 years ago bought a pair of these chassis for I think, $30 each plus shipping so $45 ea.
I had been used to stripping old organs, PAs and console stereos for parts and was a little surprised by the state of the JB amps.

My chassis was stripped of the circuit board but had most everything but tubes. No cabs so I cant comment on them.

Uh, wow... not what I was expecting. just about every component was the cheapest available. It was so bad that the cheapest available parts must have been too expensive.
I imagine they sent a grainy Polaroid of the part they needed to an unincorporated mountain village and had them made by underage farm animals working 26 hour shifts in sandals.

The switches were too "light" the bats on the toggles fell out after a few throws. The pilot lite was chromed plastic. The look of the amp seemed to say that it was a deadly fire hazard so was gutted to protect the public.
The chassis were the right layout but made from the ratty-est metal with slap dash chroming. Not worthy of the labor of building an amp. The pot seemed nice though. Sealed MIJ ALPS that looked like PECs.

I will say the sockets were just average $1 ceramic Chinese type and the transformers while looking cheap and nasty actually work and sound pretty good.

At this moment I'm tarting up an OT to use in a budget build and it really doesn't sound bad at all. Everything but the pots, transformers and sockets (if you are really cheap) goes right into the garbage on arrival.

Overall I would pass on these as by the time you pay shipping on the stuff you trow away.... You're ahead to buy MM trannies and Bournes pots.

[xtian]

I agree with you on nearly every point!

Except that I got the chassis, pots, transformers, speaker and cabinet for $100 plus shipping, threw $40 worth of parts at it, and ended up with an amp with great tone, that I am more than happy to use at my gigs so I don't have to take my #1, upon which no beer may spill, no, never.