Jumping in. Console conversion to (possibly Vibro-)Champazoo

FXBDM 1832

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Cabinetry today.

I planed the face board. It’ll need a bit of sanding but it’s pretty good. Then I mounted the chassis support inside the amp, slightly off the bottom, and carefully marked and drilled the pot location.

Then, I put the pot shaft through the hole, Clamped the face, and drew my sawing lines from this position.

Note that the lines on this picture are a previous try. The real lines are on the back side, since I traced them from the cabinet sides.

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View from inside the amp.
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I hope those tubes won’t get too hot. Maybe I will have to put some sort of heat shield on that side.

Now the next step is to cut the excess wood outside the line and especially cut the speaker hole.
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Stay tuned, and thanks for listening!!
 

FXBDM 1832

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Speaker hole done!

I made a jig for my router. Just a piece of plywood with a small pivot hole.

Worked like a charm.

One of the advantages of having a scrap wood workbench is that I don’t mind screwing my workpiece right into it.
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Did about halfway from the back, then about halfway from the front. My « about » was pretty precise, I had maybe half a mm of wood remaining and could just knock the piece out.
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Now it’s roughly trimmed, glued up and clamped.

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Tomorrow, I’ll trim the top to size with the router, install the baffle and speaker, and hopefully manage to go to the electronics store for a few missing pieces.

This is proceeding surprisingly well, and updating this thread is an important part of the motivation for me. It keeps me moving forward, and especially makes me more careful about accuracy and nice work.
 

FXBDM 1832

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And now with the round overs.
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I was not planning on the bead all around, but I slipped a bit while routing one corner and did as much as I could to correct it. I will have to soften the remaining Nick as much as I can and live with it.
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The bearing also left a little mark, I’ll see if I can’t steam that out.
 

FXBDM 1832

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I spent some time planning the layout of my tremolo, which I lifted from the Vibro-Champ. Could anyone double check this please?
VC Trem.png
VC Trem lyt.png


I know the intensity pot should read Reverse Log...

Also, I have been assuming that this circuit can just plug in to a 5f1 without other modifications. I base this on the fact that the Kalamazoo 1 and 2 seem identical beyond the trem circuit. Am I making a silly mistake there?
 

FXBDM 1832

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Some good progress tonight. I soldered in the fuze, and installed a terminal to plug the heater wires to.
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Tested the transformer and I get 325-0-325 from the primary, 7.1v from the nominally 6.3v heaters and 5.7v from the 5v circuit. I read that being slightly high was normal without load, so far so good.

I also drilled the holes for the tremolo controls and switch, as well as the 12ax7 socket. Dry fit test and we are starting to see something that looks like an amp!

0AF43DC6-6E11-422F-B937-59B0D82F4B0C.jpeg
 

FXBDM 1832

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Quiet evening tonight. I spent some time preparing my build by checking each component against the schematic, measuring it, and punching it into an index card with notes about where it goes.

It appears I am missing one value of resistors, so a trip to the store is in order.

And then, the real soldering begins!
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FXBDM 1832

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I finally got some soldering done.
E18A2030-7ABB-4EB7-AA7B-22FCE51CA955.jpeg

a few observations, in no particular order:

The actual dimensions are much smaller than what I imagined while working on the schematic. I was worried about some components reaching from pin to pin, but everything is long enough. Soldering tiny components directly to the pins requires a lot of hands!

My new powerful soldering iron makes a huge difference.

Preparing the index cards was a large help. I double checked everything again against the schematic and layout (and found an error) and tested conductivity after soldering all the components.

I copied the tube pin outa on my layout, and that was huge help in double checking my work.

Keeping things neat is harder than I expected. I can see the attraction of boards now.

Next step: connecting the filter caps and power supply, and making sure all the grounds are connected properly.
 

FXBDM 1832

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Do you guys have a special catch phrase when something starts making sound? « It’s alive » maybe?
 

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FXBDM 1832

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so, it works at low volume. A bit noisy, and it completely farts out at even medium volume. This could very well be a problem with the antique 6v6. I just had to try.
 

FXBDM 1832

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Ok, after a long night of tossing and turning and wondering, I have a few hypothesis, in order of probability

Current symptoms: Fine at low volume, slight white noise when turning up, becomes quite noticeable at higher volumes (think barely tuned radio station). Guitar sounds through fine at low volume, but as soon as you add a bit of volume it completely craps out with heavy unpleasant distortion. Nothing in between.

Video of the radio noise issue:



1) the 6v6 is bad. This would be very likely as it's the original, and the bakelite base crumbled in my hands when I removed it from the amp originally (the guiding centre pin snapped off, but you can still see the indent so I know it's in properly). I also ran it for a few seconds without the speaker connected (whoops) and it definitely arced

2) Lead dress issues. This could account for the radio-style noise, since it definitely goes up when I turn the volume knob. I must admit I got a bit excited yesterday and finished up the amp a bit quicker than I intended. Likely culprits are the volume pot / power switch leads and, well, everything else really.

IMG_0351.JPG

3) Something wrong with my layout. I don't *think* so, since the amp is producing guitar sounds, but I definitely have to double check everything. I tool voltages measurement and everything seemed within specs, but I was a bit tired, so I will try again bright eyed tonight.


So current plan is to

a) Double check the whole thing with schematic and layout in hand. Note voltages again and compare to known good specs.
b) Wait for my new 6V6 to arrive (they were marked as "released from Russia" on the 14th, but go figure if they physically made it out before the current unpleasantness. No use in exploring a lot further with the suspect power tube
c) While waiting, I might try to unhook the volume pot / switch and move it around, see if it improves things
d) finish the cabinet and the faceplate while waiting for the tube.
 

FXBDM 1832

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FWIW, here are the voltages I noted when I powered the thing up yesterday:

No Load:

B1: 441v
B2: 437v
B3: 429v

Load:

B1: 344v
B2: 299v
B3: 237v

12AX7:
2: 0
7: 0
3: 1.462v
8: 1.230v ( I had 0 on this for a bit, but when I corrected the NFB boo-boo it reappeared)

6V6GT:
3: 335
4: 304


When I measured the PT it was 325-0-325 (nominally 280-0-280 according to the schematics)

Those measurements did seem to change by the end of the night, but I was also tired and worried about making a mistake, so I decided to re-measure after a night of rest. More to come.
 

FXBDM 1832

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What's with the plate voltage on the 12AX7s? Did you finish wiring V2 since the pic?
The unwired socket is the tremolo socket. I left that for after the amp was working properly.

Forgot to measure the plate voltages on the preamp. I will do it tonight.
 

FXBDM 1832

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Well, ladies and gentlemen, it WAS lead dress and oscillation.

i was re-measuring the voltages, and tested something I thought I had noticed yesterday while really tired. The voltages were on spec with the volume at zero, but Voltages everywhere dropped severely when I raised the volume. So I figured it might be the volume pot acting up (it’s original to the donor amp).

I lifted the leads and connected them to a spare pot I had lying around and the situation improved. When I started fiddling around with the pot I noticed I could definitely change the warbling sound just by moving the return lead from the pot. I got both leads out from under the other wires, pulled them straight up from the amp and Lo! It worked like a real amp. I connected the wires back to the original pot and it still worked perfectly. One new lead and two tie wraps later and Bob’s your uncle.
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I also added an artificial heater center tap and now the hum is quieter than the hiss from the guitar.


Final voltages:

B+1: 344
B+2: 303
B+3: 252

12ax7

1: 143
3: 1.55
6: 145
8: 1.43

6v6

3: 330
4: 298
8: 17

all in all a great night. My only regret is that I ordered a new 6v6 this afternoon in case the Russian ones never showed up. Ah well, I’ll have spares.
 

FXBDM 1832

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Dry fit test with the cab unfinished.

It’s a looker if I may say so myself.
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I might need to move that OT around a bit…
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I managed to reuse the baffle of the donor amp for a bit of a throwback look.
 




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