High Power Vibro Champ build

jsnwhite619

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I started not to post a thread on this one, but I had so much trouble with it I figured it would be a good roadmap for others down the road to AVOID my issues.

The chassis came from the Zach guy on ebay who makes the chassis. I've gotten a few other from him, no problems, but I guess is measurements are off on his CNC because I had the same issues with the screw holes on my preamp sockets as @Phrygian77 did with his - I had to drill and file them out to fit. No biggie, but it takes a bit more time to do and do it cleanly than just running the screws and nuts. I also had to mark and drill the screws to hold the board on, and because I was making this as a big bore Vibro Champ, I had to drill the new hole to mount the massive 125DSE transformer, plus a couple others for ground connections. I also spent a few days researching solid state rectifiers and debating using one simply because the OT is so big and I was wondering about the proximity to the tubes.

I used an internal cap board b/c I couldn't justify - at the time - paying more than $40 for a cap can when I could use $12-14 worth of F&T's and also bump up the first one to 30uf. Add in that the size of the OT would have been subject to wherever I could fit it in relation to the cap can instead of where I wanted it -- it's huge. So, to mount a cap board, I had to cover the giant whole for the can...couldn't find any kind of premade deal to do that. Had a couple go's with tin snips and sheet metal, but wasn't happy with the end products, and I finally found knockout hole covers at Lowe's and one fit perfectly and is rock solid. But that took a fair amount of time to resolve. Cap board was easy to make - positioning it in the best place and marking and drilling the board holes AND new chassis holes again took way more time than a can ever would have.

I also cut and punched by own circuit board, like I've done for a few years now. When you see that a VC board is only 2.5" wide -- believe it! I went 2-3/4" - and a little longer - and regretted it once it was all going in. Nothing major, but just looks way more cluttered than it should compared to vintage because the leads had to be longer for the longer board. And it's closer to the sockets and controls, so it just looks jammed. Throw in the cap board and it's starting to look like a Mesa Boogie in there...

And to wind up, I have mostly only built my two-knob Harvard/5f2 and their hotrod counterparts for a couple years now...simple stuff. It's been four years since the Princeton Reverb, and that chassis was WAY bigger to work in, not counting my own choices that jammed up this one. I will admit -- this was a much more involved build than I expected - mostly because of what I wanted to do with it, not stock - but my brain just was missing gears on it. I drilled the board exactly like stock...SO many things I would do differently on the holes, layout, where the long wire leads run. I need to make a lot more notes while it's fresh in case I get dumb enough to do this again.

BUT -- it sounds pretty dang good! It is super clean - my Tele pretty much holds together with the amp on 10 unless you really dig in with it. Right now I have the 325v taps on the 290AX, but I think I'm going to swap down to 275v and have more flexibility. Right now, JJ 6v6 and 5y3 had 396v B+(109%) , 5y3 and 5881 were at 388v (approx. 80%) I think. I think I'll drop it down so the 6v6 will be safe for at least a 5y3 or 5u4, then the bigger tubes can have the 5u4/gz34/SS option -- I ordered a plug-in SS rectifier to try. No good pics of the end result yet, but here is a clip from tonight with my Tele clean and with my Blues Driver, through a Jensen C10Q. I honestly think my Blues Driver sounds better and more natural through this amp at a comfortable volume than anything I've ever played it through. The cell clip doesn't do it justice, but best I got til I can mic it. 5y3/5881.

 

telemnemonics

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Cool, sounds good!
Seems like something I might want to build, what did it end up costing you?
Planning to post more pics like guts & such?
 

jsnwhite619

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Cool, sounds good!
Seems like something I might want to build, what did it end up costing you?
Planning to post more pics like guts & such?
I think it was around $400, but that's with a speaker I didn't have to buy, and cabinet materials to build, not buying a VC cabinet. Transformers have gone through the roof in the past couple years - $160 that would have been barely over $100 then. And Hammond is still the most economical by far from what I've seen - hope they stay that way.

I'll definitely post some more pics tomorrow or the next. Forgot to take them before I stuck it in the cabinet tonight - trying to get all the high voltage out of the way while I played it. ;-) Honestly, I was looking forward to the "chassis space", but there's a lot about a Tweed chassis that I'm just used to and like at this point. Being able to lay it guts-down, live voltage out of the way is one of them. I am not a fan of just soldering a wire lead to the 68k resistors at the input jack, but I would have needed a doghouse cap board if I'd added them to the board. And all those old vintage pics with only one heater wire and the other grounded makes things look a LOT neater than you can copy today!
 

tele_savales

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Nice work, again. Sounds really good.
I've only had a few issues w Zach's chassis but I think I have a harder time coughing up for a chassis than I do for a decent set of transformers- the prices seem usurious, whether they're plated and screened or not.
 

2L man

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Right now I have the 325v taps on the 290AX, but I think I'm going to swap down to 275v and have more flexibility.
A DPDT switch on rectifier primary circuit is convenient way to do this.

Possibly another DPDT which has off position in between and two resistors on power tube cathode resistor circuit make possible to have six different operating points. Then few different power tubes can be used "correctly biased" and "biased more or less not centered" as well.

Third SPDT switch to change OT impedance between 5k and 2.5k open even more possibilities... :)

I have H125DSE biased to 60mA/5k and about 360VDC for EL34 but I have used it 45mA/5k for 6V6 about 290VDC. I have used also 5881, 6L6GA 19W coke bottle and few russian octals. Tung sol 5881 reissue is my favorite SE amp tube but I like it for PP too. I think H125DSE has very good value for money and its max 60mA bias is often enough.
 
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Huddy

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Transformers have gone through the roof in the past couple years - $160 that would have been barely over $100 then. And Hammond is still the most economical by far from what I've seen - hope they stay that way.
Don’t know if you have a CE Distribution account or not but they’ve got their own branded versions of the 290X and 1760C along with the choke and reverb driver.

Though might shake out to be the same with shipping as amplified parts retail price if you qualify for free shipping.
 

King Fan

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Nice report, nice result. I feel your pain on the chassis-chopping issues; had the same recently on my Bassman Micro. I think it’s not Zach’s fault, exactly, or mostly; most of the issues, like board mounting holes, come from the Mojo chassis he often uses as a model. And TBH the Mojo chassis I’ve used was excellent — it makes some sense they let you locate board mount screws, given boards aren’t all the same. You and I both buy into metalwork when we swap PTs, discard cans for caps, and so on. Not saying it’s not a pain… the metalwork on the Bassman Micro was almost the hardest part. Just saying in my case it was my doing, not Zach's.
 

jsnwhite619

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Don’t know if you have a CE Distribution account or not but they’ve got their own branded versions of the 290X and 1760C along with the choke and reverb driver.

Though might shake out to be the same with shipping as amplified parts retail price if you qualify for free shipping.
I had not seen these - who's gonna be the first? Specs look good on paper, hope they are made well. https://www.tubesandmore.com/produc...imary-325275v-63vct-5v-secondary-fender-champ

Nice report, nice result. I feel your pain on the chassis-chopping issues; had the same recently on my Bassman Micro. I think it’s not Zach’s fault, exactly, or mostly; most of the issues, like board mounting holes, come from the Mojo chassis he often uses as a model. And TBH the Mojo chassis I’ve used was excellent — it makes some sense they let you locate board mount screws, given boards aren’t all the same. You and I both buy into metalwork when we swap PTs, discard cans for caps, and so on. Not saying it’s not a pain… the metalwork on the Bassman Micro was almost the hardest part. Just saying in my case it was my doing, not Zach's.

Oh yeah - I know I had a lot of special cases on this on in the drilling and metalwork, but for all 4 preamp socket screw holes to be off the same amount on mine and others when none of his other models have that issue, I'm thinking something might be off. Would be curious if anyone has ever told him - I may send him a message on Ebay.
 

King Fan

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I had not seen these - who's gonna be the first? Specs look good on paper, hope they are made well.

Well spotted, @Huddy . Who makes those? I wonder. CE Dist / AES used to carry MC (Classictone in wholesale clothing) at decent prices. Could these be APD, or the MC/CT replacement company we hear about sometimes? Hmm. They look well made.
2B4A90D1-DD3E-4B33-B8B8-78A5736EF377.jpeg
 
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Huddy

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Would be curious if anyone has ever told him - I may send him a message on Ebay.
I was looking at a couple of his chassiszzzs this morning and on a couple he's got notes - "transformer mounting holes are smaller than they should be" things like that. I'm sure he makes them in batches and sometimes makes corrections for the next batch after being made aware.

Did you get your 6G15 chassis from him?
 

jsnwhite619

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I was looking at a couple of his chassiszzzs this morning and on a couple he's got notes - "transformer mounting holes are smaller than they should be" things like that. I'm sure he makes them in batches and sometimes makes corrections for the next batch after being made aware.

Did you get your 6G15 chassis from him?
That came from Mojo.

On a side note - after years of only have chicken head knobs, including my own builds with a Pro Jr, Delta Blues, and Hot Rod Deluxe, I miss the "bigger" sweep of them. Roughly a 5/8" radius to turn on the chicken head vs that tiny center knob of the witches hat... it makes the pots seem WAY more sensitive! Trying the different rectifier options and tube options tonight - I'll report back later. I swapped it down to a 275v secondary from the 325. As I noted above, 6v6 was starting at 396v B+ and the 5881 was at 388v with only a 5y3 - didn't leave a lot of room to experiment with when you're starting at the top of the limit.
 

jsnwhite619

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I am a couple months out from needing that PT, but that is exactly the one I need and its a great price. There's a companion OT that they also stock. No one knows who manufactures it?

They may not name the source - could even be an agreement not to if they aren't branding it - but would be interesting to know the country of origin. For the price, I would guess from overseas, but I could also see them being able to buy in bulk and offset the cost with other items in the catalog for the lower price if USA made. Transformer makers that ONLY do that have nothing else to balance the sales. CE/TubesAndMore has a huge catalog that could help keep the cost lower on a few transformers.
 

King Fan

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I am a couple months out from needing that PT, but that is exactly the one I need and its a great price. There's a companion OT that they also stock. No one knows who manufactures it?


You might ask 'em. I’ve had good luck calling AES customer support in years past. When the nice person on the phone didn’t know, they asked a tech person to call me back. Hey, if you find out, maybe share a PSA thread here in Shock Bros. Oops. I mean The Forum Formerly Known As Shock Brothers….
 

jsnwhite619

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You might ask 'em. I’ve had good luck calling AES customer support in years past. When the nice person on the phone didn’t know, they asked a tech person to call me back… if you find out, maybe share a PSA thread here in Shock Bros… I mean… The Forum Formerly Known As Shock Brothers….
Well be sure to stop by here first so I can be sure to see it!

Pictures coming soon, but I had a thought about the responses to this thread so far that sums up the Shock Brothers perfectly:

"This build has been the biggest thorn in my side that I can remember!"
"That sounds pretty good - I think I'd like to do that too!"

:lol::lol:
 

jsnwhite619

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This looks like a rat's nest - but it's so quiet already with an open chassis and no shielding that I'm scared to mess with it. I went through tonight with my insulated tweezers pushing and moving things, seeing if anything sounded better or different, but I couldn't get much improvement. As usual, still quieter than any factory amp I've owned, even at 10. The 6v6 is almost dead quiet, the 5881 has more noise, but it's amplifying more...I guess? Still more of just the SE hum, no buzzing or grounding noises. I used the headphone trick for the first time and was amazed at the differences, but the size of the OT still decided ultimately where it would go and that was not "the best" spot I found, but close.

Like I said, it's crowded in there.... And I wanted to show of my "amp cradle". I've got to build one of those things. Get by fine with a Tweed chassis, but the Blackface stuff is a pain to get the hardware cleared of the workbench. Probably my ugliest one in years inside, but I'm scared to change it at this point.

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For the OT size -
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1674620289483.png
 

jsnwhite619

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I also plugged into my 8" Jensen C8R closed back "Champ" cabinet tonight. That is definitely a sleeper speaker. Sounded great through that. It "sounds" like a Champ with that, and sounds like a "Fender" through everything else. I've realized that 90% of the "Champ sound" is because of the 8" speaker and small cabinet. So much more live feel/sound and response with it. For a low efficiency speaker it really carries everything from the your fingers sliding to the clack of the pick hitting the strings, and great breakup.

As soon as I get a few hours to run through different speakers/tubes one day, I'll be posting some test clips. Still may try to dirty it up a little though - it is the cleanest amp I have. Surprisingly loud and clean on 10.
 

Phrygian77

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@jsnwhite619 I don't know if you remember this crazy conversation that I did a couple of years ago, but this type of board (5mm spacing) would probably work well in a VC chassis. I'm pretty sure I had cut this one down a little bit since those boards are almost 12" long.


pxl_20210417_052556698-night-jpg.846969
 




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