How Close is a Bypassed BF Champ to a Tweed Champ?

markesquire

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I currently have a Victoria 518 (tweed champ) that I love. I also want a BF Vibro Champ (probably build).

I've heard that lots of people include a switch to bypass the BF tone stack (or at least the mid resistor) on their BF champs to make the tone more "tweed" like.

How close does a bypassed-tone-stack BF champ get to a tweed champ? I would want the "tweed" setting to be capable of the same low-fi mid-based tweed cleans, which I love (I don't just want the tweed section to be a fire-breathing gain option only).

Bonus question: who could build me one?
 

King Fan

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Interesting question. In fact, how similar is a '60s champ to a '50s champ in any case?

But the title threw me. I thought you meant bypassed in the sense of a V1 cathode bypass. Not that that makes perfect sense, but it is what I think of as ‘bypass’ in this setting. Hey, though, no V1a bypass would prevent fire-breathing.

I’ll be interested what folks think who’ve tried a tone-stack lift. Hmm, are you hoping it’ll be a lot like a 5F1? Or a lot different?
 

snottyboy

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Okay, I'm half your guy. I've got a tone-stack lift on one of my '68 Champs. The half I'm not: I've never played through a Tweed Champ. Here's what I can tell you about my '68...I've got a Weber 8A125 and great old tubes in it. Tone stack in play, it's a great small room amp both clean to mean, and takes pedals extremely well. Great, great tones. Tone stack lifted, it is more immediate, louder, but still has a nice range of clean(ish) to angry. Mids are always there, no scoop. Takes pedals well, but more picky. In all, I love this amp. Have had it now for a dozen years or so. The person I bought it from has said on a few occasions that he would buy it back if I were selling. It is so useful for practice/small combo playing, and the tones are glorious. For reference, I've played since 1979, mostly through my old '68 Vibrolux Reverb (which is always my tonal reference). This Champ is right there for me. No, it is not a toy or beginner amp.
 

markesquire

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Hmm, are you hoping it’ll be a lot like a 5F1? Or a lot different?

I'm hoping that the tone-stack-lifted sound is exactly like a 5F1. If that were the case, I might even consider selling my tweed champ clone because I'd have one great amp (with tremolo) that can perfectly nail both BF and Tweed tones (clean to dirty).
 

bebopbrain

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Change an AB764 Vibro-Champ into kinda a 5F1 tweed champ?

Get a triple pole switch to connect (or disconnect) three things to ground.

The AB764 has a 15K "midrange" resistor to ground in the tone stack. The AB764 has a cathode capacitors (to ground) on the first two 12AX7 stages.

In AB764 mode you want everything connected to ground (the 15K reistor and both cathode caps). In 5F1 mode you want those same 3 components disconnected from ground.
 

OldPup

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I tried to research the answer to your question by looking at wiring diagrams for the 5f1 and the Vibro Champ. I don't know enough about which capacitors dump which frequencies, so that didn't go far. If you totally bypass the VC tone circuit, that sounds like you'd be bypassing all tone capacitors. I don't think that will yield a Tweed sound. The 5f1 has tone circuitry, you just can't adjust it. The 5f2a (the Tweed Princeton) is a 5f1 with adjustable tone.

I'm curious if you're basing this build on something in particular you've come across. It almost sounds like you want Tweed sound with built in tremolo (okay, confirmed by your last post). If that is the case, consider a 5f11 build, which is a Tweed Vibrolux. Mojotone sells those kits with a 10-inch speaker in an oversized cab, which makes the amp sound bigger. You can probably find a vendor closer to your neck of the woods.

If you want to play at bedroom levels (ha!), drop a 5f2a tone circuit into a VC build. Since it's your build, you should be able to spec an 8-inch speaker. You'd have one tone knob free to imagine something else to do with. Maybe adjustable negative feedback or whatever.

I built a 5f2a recently and it's awesome. It sounds great clean, it sounds great breaking up, it sounds great overdriven. Its oversized cab means it sounds much bigger than you'd think an 8-inch amp would. It definitely gets loud.
 

dinomike77

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Seeing as you state that you *have* a tweed-style and *want* BF tones, rather than the other way around as some have given suggestions for, I’d say use an EQ pedal to scoop mids. This will lower your gain as well, of course.

I have a Gries 5, which does the BF Champ with a Gain knob that piles on the mids to overwhelm the BF tone-stack, resulting in what the manufacturer states is “essentially a 5F1 Tweed Champ.” Going from the BF to the Tweed territory greatly increases the gain and has given me quite a lesson in how mids and gain are associated in a simple amp circuit.

I believe that using an EQ pedal to do what my Gries does, but in reverse, would be a good way to start. Not 100%, but possibly even more versatile.
 

SnidelyWhiplash

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Two completely different amps in terms of circuitry & sound. If you try to turn a BFC into something more " tweed " like, I'm afraid you'll have an amp that will leave you disappointed. It will be neither and nor. :(
 

markesquire

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Thanks for the input everyone - please keep it coming!

To clarify, I don't just want a tweed amp in BF clothing. I actually want pure BF tones, but wonder whether that single BF amp could also cover tweedy tones with a flip of a switch, giving me 2 amps in 1 (instead of having to have 2 separate amps). I just really enjoy the warmth and mids of the tweed and want to have that tone available, but also want glassy BF tones too.

Also, some of these comments make me wonder if there are a bunch of different options here: (1) bypassing the tone stack altogether, (2) bypassing only the mid-scooped component, etc.

The EQ pedal idea is also interesting: essentially put a mid-scooped EQ in front of a tweed champ. This would reduce mids and gain, but where does the "glass" come from in the BF circuit, and would an EQ pedal provide it?
 

King Fan

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I don't know here. Seems to me it'd not only be hard, but maybe kinda pointless, to replace a 5F1 with a modded BF/SF Champ. A complex switching arrangement *might* do it -- but that's a tricky build, and where you gonna put all the switches? Heck, how do you even label the different switches? :)

These are different but classic, simple, elegant little amps. What do we gain by trying to put two in one package: floor space? :D
 

loopfinding

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Change an AB764 Vibro-Champ into kinda a 5F1 tweed champ?

Get a triple pole switch to connect (or disconnect) three things to ground.

The AB764 has a 15K "midrange" resistor to ground in the tone stack. The AB764 has a cathode capacitors (to ground) on the first two 12AX7 stages.

In AB764 mode you want everything connected to ground (the 15K reistor and both cathode caps). In 5F1 mode you want those same 3 components disconnected from ground.

and then the 5E1 ended up cathode bypassing the first stage anyway. in the vibrochamp there's also a 2.7k negative feedback resistor instead of a 22k. but that's about it, the circuit is basically the same. if you left the cathode bypass caps in and didn't change the feedback, it could be even more of a screamer than a 5f1.

if you want to lift the mid portion alone i don't think it will be as angry as a 5f1 or as tweedy (less gain). but that is a cool mod too.

i say do it. purity be damned. i'd rather have the vibro champ and the option to lift personally.
 

dankilling

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Could like.y be done similarly to the tone king gremlin- one input goes to a 12ax7 with the 5f1 preamp, and the other into the blackface champ preamp and tremolo circuit. Build it in a PR chassis and everything would fit neatly, plus you could use a 10” speaker. Sounds like a fun project o me.
 

2L man

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I built this link

http://www.planetgaa.com/amp/my5f2a.html

modified Princeton for 5881 tube and I really like its versatility. Additional master volume and NFB potentiometer allow lots of different sounds.

Electrically tube rectifier has very little effect on SE amp so using silicon rectifier save money also on power transformer.

Toroidal PTs are cheaper and reduce hum when their electromagnetic stray field is weaker and strongest on hole axis so mounting flat to chassis direct field away from pre amp and output transformer. Antek is only USA brand I know and their 50VA tube PTs cost only $28. Hammond 125DSE OT is also reasonably priced and good for 70mA bias which is enough up to EL34. For lower power tubes H125CSE is fine.
 

72_Custom

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I've built both a tweed Champ and a Vibro Champ. I tried lifting the tone stack ground on the Vibro Champ and it really turns it into a screaming beast. I've heard some people use a cathode bypass cap on V1A of their tweed Champs, but mine doesn't have it, so there was a big difference between the two amps at that point. Because I had an extra hole in the chassis, I ended up putting a switchable 47K Ohm resistor in there for a serious mid-boost (and mild gain boost). This gives a reasonable approximation of the tweed thing.

But this discussion has me thinking maybe I should lift those cathode bypass caps instead. After all, the three things in question (apart from the NFB) are all going to ground, so the switching wouldn't be THAT complicated.
 

markesquire

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I've built both a tweed Champ and a Vibro Champ. I tried lifting the tone stack ground on the Vibro Champ and it really turns it into a screaming beast.

But . . . did the VC with the lift-mod sound the same as the tweed champ?

I keep hearing people say that the VC lift mod turns it into a "screamer" or a "beast" or whatever, which is fine I guess, but what I really love about my tweed champ is its clean and semi-clean tones with lots of mids. If the VC lift mod just turns it into a gain machine without any mid-based cleans, that's not what I'd want.
 
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peteb

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I have experimented with the tone stack lift on a bf champ, and I have demo’d a real tweed champ.

the tone stack lift takes you there and then some. You can easily have sustaining feedback. The volume is twice as loud but distorted.

i recommend putting in a pot where the mid resistor is so that you can dial the tone stack in or out as much as you like.
 

72_Custom

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But . . . did the VC with the lift-mod sound the same as the tweed champ?

I keep hearing people say that the VC lift mod turns it into a "screamer" or a "beast" or whatever, which is fine I guess, but what I really love about my tweed champ is its clean and semi-clean tones with lots of mids. If the VC lift mod just turns it into a gain machine without any mid-based cleans, that's not what I'd want.


Sorry, I think I phrased my response poorly. With the tone stack lifted, there are three remaining differences between the tweed and BF champs: cathode bypass caps on the preamp tube, the amount of negative feedback, and the filter capacitors network is a bit different. The main reason why the BF (Vibro) Champ screams is that the two cathode bypass caps are still present. If you could lift (at least one of) those in addition to the tone stack, then you should have something pretty darn close to a tweed Champ. (I haven't personally done this yet, but the timing is convenient because the Vibro Champ just so happens to already be on my work bench)
 

The Ballzz

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Compare these!

Champ-5F1-Schematic.jpg
Vibrochamp-AA764-schematic.jpg
 
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Greggorios

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I have a Gries 5 which is a BF Champ (AA764) with a a 12" Emminence GA SC 64 and a few tweaks including a T/M/B tone stack that can be blended out of the circuit. The result is what's been described as "approaching" a Tweed 5F1 and I think that's pretty accurate. It's not gonna replace a tweed but gets pretty damn close. I like to set it "right at the edge of breakup".
 




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