Anyone Wrecked a Vibrochamp?

[bcmatt]

Hey Thanks!
So, were you able to keep the same transformers then?
I notice the addition of a 40uF filter cap as well.

I'm wondering whether to do do what you did as well. I know that some have successfully done a transformation like this keeping the 6V6 and had success as well, but I haven't found actual schematics.

[Lonely Raven]

Question about the way you guys are building this.

In a typical Trainwreck, one of the key design concepts is that the power tube distorts first. Is still something that you are incorporating into your Champ-'wreck, or are you just modding the pre-amp and calling it good?

I'm a complete beginner (so I'm probably talking out my arse), but IMHO, I would be designing around that same concept *and* copying the preamp.

[bcmatt]

It's Ok Raven, I'm a complete noob to designing any amp as well. My only experience so far is building a few amps from kits.

My goal was to take my vibro-champ kit that I previously made and swap in an Express preamp. I honestly don't know how well it will interact with the champ power section, but I figure that it is low enough powered that I should be able to get it really pushing on the power tube as well. Then again, maybe the champ won't do that in the first place????
But really, I don't know what I'm doing, so I don't know what it will take to match the preamp up to the power amp so that it balances out the distortion nicely. It's a wild guess at this time how they will interact.
It will likely take some matching and tweaking that I am incapable of.
So, I'm doing it on this board with the hope that those in the know will help guide me into something that I'll like the sound of. I'm hoping to increase my understanding along the way as well.

[Lonely Raven]

Well, you still know way more than me!

Just pointing out the fact so maybe someone can throw you some suggestions. I love Champs, and I'd love to follow up on your build and try building your wrecked champ after you get some of the details worked out.

Selfish of me I know, but I'll just wait for you and all the other smart guys to do all the hard work for me.

[Andy Le Blanc]

Ive used champs to play with multiple gain stages........ they sound great
but the thing that seems to be the weak link is the out put tranny
something about a SE tranny, square wave, and core saturation......
I've cooked a few of those little buggers.......everything else in the circuit
was good...... but cranked with everything full up they didnt last too well
that would be the one part I'd be carefull sourceing , wouldn't risk fry'in
an original

[invalidcd]

Hey Thanks!
So, were you able to keep the same transformers then?
I notice the addition of a 40uF filter cap as well.

I'm wondering whether to do do what you did as well. I know that some have successfully done a transformation like this keeping the 6V6 and had success as well, but I haven't found actual schematics.

yeah i was able to use the transformers, but i also converted a champ 600 one of the new ones , and the PT was 275VAC no CT I used a bridge rectifier ,and add extra gain stages and everything was just fine. the 6v6 and el84 really only need about 380V . I will tell you one thing though even with extra gain stages using a 6V6 ,it was not any louder than the champ 600.

But Seriously the only thing i used from the champ was the PT and OT
switches, and a handfull of caps.

Today I did another conversion. i got ahold of some gut shots of a DR.Z Mini-Z
And drew up a schematic .
This amp is the king of SE amps, it loud , and very dynamic , I was really surprised , and it only uses 1-12AX7 and 1-EL84 . Same as before I used the champ PT & OT.

The Mini-Z is much easier and sounds better than any SE Wreck or SE amp Ive heard. if you want i can PM you the schematic that i made from the gut shots.

[dartanion]

A lot of Champ OTs are way undersized (similar to a Fender reverb transformer in size), as well as the PTs being weak too. Allen amps SE OTs are quite good, made by Heyboer to David's specs. I've use this OT on my Bastard Champ (EL34, GZ34, 5F2A tone control, etc.) and it has held up just fine and sounds great.

One thing to note here is that the PI has much to do with the tone of a Wreck, which is not present in an SE amp. You have another triode free, so you can add a stage to approximate the Wreck PI gain and clipping. Push a little more signal to the 6V6, it needs it. You can also increase the grid leak to 330K - 470K for extra drive.

Another approach is to move the tonestack from the "Fender" position to after the last gain stage to reduce gain suck. Additionally, that extra triode could be used for a CF to reduce insertion loss into the tonestack.

I wouldn't rest on the Mini-Z as "The Best SE Amp" quite yet. There are plenty of more avenues to explore.

Peace

[bcmatt]

Invalidcd - PM sent. I'm interested to see your project for sure.

Dartanion- I'm not sure how strong my transformers would be. They are the ones that came with my ceriatone vibrochamp kit that I made a while back. IS there a way to use a DMM to find out the particulars of it, or is that not really possible? I'd like to use these tubes and transformers if at all possible, otherwise I might as well start a project from scratch.

Also, I was thinking of actually trying to incorporate that last unused triode back in to the schematic right this minute, but I'm not sure exactly how I would do that. I was thinking of possibly of a cathode follower as well as adding a presence control off that last triode. Any thoughts?

[dartanion]

Hey Matt,

A CF is very easy to implement and would make the preamp more like a Komet. As well it decreases the insertion loss into the next stage, which would be the output tube. This can more easily drive the power tube. Moving the tonestack to the "Marshall" position after the CF is also an option, but now you are straying from a Wreck/Komet.

If you are using Nik's OT, I believe he told me they are good for 15 watts. So, you could try an EL34 if your PT has the filament current available. I don't recall the specs on his Champ PT.

I think though that to make it more Wreck like, that last triode should be used for a gain stage that approximates PI gain and clipping, otherwise a critical element of the Wreck is plain missing.

[bcmatt]

Hey Matt,

A CF is very easy to implement and would make the preamp more like a Komet. As well it decreases the insertion loss into the next stage, which would be the output tube. This can more easily drive the power tube. Moving the tonestack to the "Marshall" position after the CF is also an option, but now you are straying from a Wreck/Komet.

If you are using Nik's OT, I believe he told me they are good for 15 watts. So, you could try an EL34 if your PT has the filament current available. I don't recall the specs on his Champ PT.

I think though that to make it more Wreck like, that last triode should be used for a gain stage that approximates PI gain and clipping, otherwise a critical element of the Wreck is plain missing.

Using an EL34 sounds interesting to me. However, I have no idea if the PT has the available filament current. Would dropping the 5Y3 free up enough? Is that the only thing that would hinder that swap? Anyways, I think I want to work through the current tube compliment for now to come up with a schematic first.

I really want to go with your idea of the added gain stage. I've never done such things before, so do you have suggested resister and cap values? Can I put a presence control off the cathode as well, or is that a waste of time?

[bcmatt]

Here is what my schem is currently looking like as I work on it:

[dartanion]

Looks good, but I would drop the bypass cap on the new stage. Might work though, but may not. Easy to try it both ways. Presence is really nothing more than variable NFB, so it should work fine. Just us the design from an Express. I prefer SE amps without NFB, but that's just me. NFB will knock down the output too.

[bcmatt]

Looks good, but I would drop the bypass cap on the new stage. Might work though, but may not. Easy to try it both ways. Presence is really nothing more than variable NFB, so it should work fine. Just us the design from an Express. I prefer SE amps without NFB, but that's just me. NFB will knock down the output too.

Well, here is my latest; as per your suggestions. Am I getting closer to something workable? Also, how can I decide the missing values?
Do I need more filter caps on that B+ rail? How would I know?

[jjman]

BTW I think the 330pf cap on the 6v6 is one of those "tone robbing" band-aid solutions that Fender used to help avoid parasitic oscillation. I removed the one on my VC and it triggered a “buzz” on low notes. I then changed that grid wire to shielded and the buzz disappeared.

My VC distorts well when cranked. I can’t imagine adding 2 more stages to it. I understand that the cathode resistors and plate voltages matter.

I’ve always wondered how the Champs get distortion with so few stages. I don’t think it’s possible that they clip in the preamp. Or is it? I guess I need to scope my VC and homebrew Tweed Champ.

[bcmatt]

hey JJman,
Thanks for the 330pf (tonerobbing) cap tip.
My VC distorts nicely too when cranked, but only with humbuckers. Maybe I shouldn't touch the thing, and should just use my pedals, but I guess, I want to play with it. I want something small and fun to play with that can clip at slightly quieter volumes. You know, I don't know if the preamp clips at all either- I was assuming that it doesn't really, that was my motivation in converting the tremolo to more gain stages.

On another note, did anyone else know about this->
https://tubeamparchive.com/viewtopic.php?p=54227#54227
I hope it wasn't meant to be a secret, but I want to know about it, because it sure seems to me that it applies to this project.