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

[FXBDM 1832]

Finished wiring the tremolo circuit. Ran into all kinds of issues, most solved now, except a hum that only happens when the tremolo is turned off at the switch. I will have to do some more testing and thinking tomorrow.

One possible thought: the intensity pot is affecting the bias of my preamp tube. The VibroChamp circuit seems to have a special cathode setup so I will look into that part.

 

[FXBDM 1832]

Video of the amp and tremolo working.
You can hear the 120hz hum at the end when I turn the intensity up and close the tremolo switch (it’s wired to shunt the signal to ground, like the foot switch)



At this stage, the hum is a minor irritant. It disappears if I turn the intensity down, I know it’s not the tubes, I know it’s the trem circuit ( unsoldering the trem from V1b removes it completely). It might be lead dress, it might be that the trem is too close to the rectifier, etc. The tremolo itself works well (except for the fact that the intensity pot is audio taper instead of reverse audio, which I feel kind of silly about)

I detected a few soldering problems while testing the tremolo, so I solved those. For all intents and purposes, the circuit is done.
One thing I might want to address Is that I think I might have too much gain on tap. The amp is fine when playing on the low output with single coils, but Humbuckers make it go out of control pretty fast. I might try removing the cathode bypass cap from V1a to see.

 

[FXBDM 1832]

Ha, it turns out the NFB was wired improperly and was grounding itself (I connected it to the side of the OT that did not squeal loudly, but didn’t realize it was also the grounded side, so the NFB didn’t make a difference at all when it was plugged vs unplugged). That should help with the « too much gain » thing. It does rob a bit of my tremolo intensity though...

 

[FXBDM 1832]

A quick question:

I am wondering about my NFB lowering the intensity of the Tremolo, and would like to remediate it.

I noticed looking at the schematics of the 5f1 Champ and Vibro-Champ that the NFB inserted at a slightly different place on the V1B cathode:

5F1: Between the Cathode and the Cathode resistor

Vibro-Champ: Between the Cathode resistor and another small resistor to ground

I also notice that the NFB resistor is much smaller on the VC (2,7K vs 22K). Would that be a solution to my problem, do you think?

I might as well try it, it's not a very hard mod.

 

[printer2]

A quick question:

I am wondering about my NFB lowering the intensity of the Tremolo, and would like to remediate it.

I noticed looking at the schematics of the 5f1 Champ and Vibro-Champ that the NFB inserted at a slightly different place on the V1B cathode:

5F1: Between the Cathode and the Cathode resistor
View attachment 962163

Vibro-Champ: Between the Cathode resistor and another small resistor to ground

View attachment 962164
I also notice that the NFB resistor is much smaller on the VC (2,7K vs 22K). Would that be a solution to my problem, do you think?

I might as well try it, it's not a very hard mod.

That should help you out.

 

[JSMac]

I wanted to add a NFB circuit in a 5E3 build in an attempt to tame it a bit. I couldn't decide what value I liked so I made it variable via a pot. It can go from no NFB to about 33k. My point is that it really makes a range of difference so you may want to experiment.

You may want to experiment with the cathode bypass cap value.

 

[NTC]

The 2700 in the vibrochamp is because what you are doing is making a resistor divider with the 47 ohm resistor. In the champ, the 22k makes a divider with the 1500 ohm resistor.

 

[FXBDM 1832]

Well, tonight I rewired the V1b cathode to match the vibro-champ. Works well, and it took care of my intensity problem. I also switched the intensity pot to a proper reverse log taper, and put the Tremolo cathode led on the face of the amp.

Circuit is basically done. I do wish I could put a NFB switch but I am starting to run out of real estate. I will put everything together, live with it for a bit, and see if I really need to change things up.

I also sanded the cab and put on the first coat of poly.

Really entering the home stretch, now.

 

[FXBDM 1832]

Still to do: second coat of poly, and faceplate.

 

[dankilling]

how does the tremolo LED work?

 

[FXBDM 1832]

how does the tremolo LED work?

It replaces the cathode resistor on the first stage of the Tremolo 12ax7. The fun thing is that it blinks in time with the oscillation, so it serves a triple purpose: power light, Tremolo on/of indicator and Tremolo speed indicator.

I saw the idea in a few places but most pointed to Valve Wizard. https://www.valvewizard.co.uk/trem1.html

 

[Mongo Park]

Well done, nice build, nice problem solving
Wrap er up and play music.

 

[FXBDM 1832]

Well done, nice build, nice problem solving
Wrap er up and play music.

Thanks!

I still need to figure out the faceplate hole spacing

 

[FXBDM 1832]

Some pics of the final finish.

I am now debating whether it even needs a faceplate. Maybe labels would fit its heritage better.

Had some fun playing it. It gets good breakup pretty early on the dial, especially with humbuckers.

The tremolo is pretty fun for my poor rendition of My Baby Shot Me Down.

It does tend to crap out on loud chords.The 6v6 is a bit suspect so I will try the new one I have lying around.

 

[FXBDM 1832]

Still working on the build. Here is my faceplate nearing the final stage

I measured the chassis and made an accurate template in a faceplate creation program

drilled holes in 3mm clear acrylic

and painted the back in Turquoise.

Fit test:

Not bad. Now the plan is to scratch off the paint for the lettering and use a dark brown for contrast.

The back panel is cheap MDF that was on the original console. I don’t like the result, so I will use it as a template and re-do it in a material I can actually finish properly.

I might even make it so it fits inside the cab cavity and presses on the faceplate, kinda like old Marshalls.

A family member who’s a recording guitarist came by and liked it. Listening to this guy play on my stuff is always fun: I can’t really blame the gear for my poor results afterwards

 

[Esquier]

Jesus look at the size of that power transformer...

Should make a nice amp. Lots of room to work too. I did a few of these in tabletop radios that came out really good. I used a choke in mine and they turned out extremely quiet. They were a 5c1 thing with a beefed up psu and star ground.

Have fun!!!

I have a radio chassis like this one. Check out the big block of wood sandwiched underneath the power tranny. It's really not that big. They were built down to a price, that's why the output tranny can hide inside

 

[FXBDM 1832]

With the faceplate installed. The handwritten look is done on purpose,

still having a few teething issues, but fun to play.