New amp concept ... maybe

4114Effects

Been tinkering around with a little project over Christmas. Not sure if this has been done before? It's a pretty simple one - loosely based on a Champ, but with the preamp going to two separate single-ended power valves - one El84, one 6v6. Each valve has it's own volume control so you can mix and match.

Works better than I expected too - each power valve has it's own flavour. Brightness and harsh breakup from the EL84, smoother breakup, fatter tone and more bottom end from the 6v6. I deliberately didn't add a tone control to let the valves speak for themselves a bit.  Loads of fun to mix them together, and pretty raucous when they're both on full whack. 

The speaker is an old Elac 10" Alnico which works very well and gives it a more vintage flavour too. Cabinet is pine with a thin baffle so it's lively and resonant, in a good way.

Have to say this is one of my favourite amps to date.

Amp covering is a new one ... might not be everyone's cup of tea but I like it

Please excuse the messy workbench ...

RaymondLin

Erm, yes, I think Bogner has an amp with similar idea.

http://www.bogneramplification.com/products/amplifiers/140


very nice though, come a long way since the Champ I got from you.

Strangefan

I would 100 percent rock that 

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RaymondLin said:

Erm, yes, I think Bogner has an amp with similar idea.

very nice though, come a long way since the Champ I got from you.

Knew somebody would have done something similar. Can't be many unique circuits left to try.

RaymondLin

4114Effects said:

RaymondLin said:

Erm, yes, I think Bogner has an amp with similar idea.

very nice though, come a long way since the Champ I got from you.

Knew somebody would have done something similar. Can't be many unique circuits left to try.

But good luck finding one! They didn’t make many and I think this is such a cool idea.  It’s 2 amps in one.

RiftAmps

I once built an 18w Plexi with OP valve blending. Used a dual-gang potentiometer to send the PI outputs to either a pair of EL84s or 6V6s. Difficult to get right so well done on this build, lots of tones on offer.

IIRC it's pretty common in the DIY HiFi community, and Rat Valve Amps offers it on some of his SE rebuilds

mixolyd

Didn’t Egnater do a EL84+6V6 amp like that a few years ago too?  I think it may have just been switched rather than blended though.

PhilKing

I have a couple of amps from the 1990's built byJohn McIntyre (who designed the Lexicon Signature 284), which have a 6V6/EL84 power section.  They work as separate amps though, and you can adjust the output of each.  They both have emulated recording outputs, so you can blend them via a mixer.

ICBM

The Mesa Blue Angel is also 6V6 and EL84, but it’s push-pull and only switched for either or both, rather than having a volume for each.

Sassafras

Love the Paisley look.

DartmoorHedgehog

How does the output to the speaker work?  Are both valves using the same output transformer (with two primary windings?)
Cool looking amp BTW

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DartmoorHedgehog said:

How does the output to the speaker work?  Are both valves using the same output transformer (with two primary windings?)
Cool looking amp BTW

Same output transformer. I've chosen a primary impedance  value that's halfway between single ended and parallel single ended. I never look on guitar amps as an exact science. If it sounds good and doesn't catch fire them I'm happy. ;-)

ICBM

4114Effects said:

Same output transformer. I've chosen a primary impedance  value that's halfway between single ended and parallel single ended. I never look on guitar amps as an exact science. If it sounds good and doesn't catch fire them I'm happy. ;-)

Exact science is for hi-fi amps . I've always thought that the two things are almost diametrically opposite. Obviously there are some elements in common, but in general, the last thing you want is a perfect reproduction of the output of an electric guitar - if you want to see what that sounds like, just DI one. I have actually used that sound on purpose when I want an 'acoustic-like' sound, but it's really very different from even a normal clean electric guitar tone.

sgosden

That's really cool. Love the Paisley too. 

darcym

that's a really great concept, and I love the champ format, I'd love to give this a go please

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ICBM said:

4114Effects said:

Same output transformer. I've chosen a primary impedance  value that's halfway between single ended and parallel single ended. I never look on guitar amps as an exact science. If it sounds good and doesn't catch fire them I'm happy. ;-)

Exact science is for hi-fi amps . I've always thought that the two things are almost diametrically opposite. Obviously there are some elements in common, but in general, the last thing you want is a perfect reproduction of the output of an electric guitar - if you want to see what that sounds like, just DI one. I have actually used that sound on purpose when I want an 'acoustic-like' sound, but it's really very different from even a normal clean electric guitar tone.

Always makes me laugh when I read amp building forums and people are arguing about correct voltages and impedances for valve amp stages to the nth degree.

In reality most great sounding guitar amps are based on old Fenders and Marshalls, which in turn were badly copied from radio handbooks and built using whatever random parts they could get hold of. 

jpfamps

4114Effects said:

In reality most great sounding guitar amps are based on old Fenders and Marshalls, which in turn were badly copied from radio handbooks and built using whatever random parts they could get hold of. 

That's true to a certain extent of Marshalls but certainly not of Fenders.

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jpfamps said:

4114Effects said:

In reality most great sounding guitar amps are based on old Fenders and Marshalls, which in turn were badly copied from radio handbooks and built using whatever random parts they could get hold of. 

That's true to a certain extent of Marshalls but certainly not of Fenders.

Ah, my mistake, I always thought the Early Champ designs were based on the RCA tube handbooks? 

darcym

can I have a go on it please ?

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darcym said:

can I have a go on it please ?

Not sure how we'd make it happen as you're miles away and we're on lockdown, but feel free

ICBM

4114Effects said:

Ah, my mistake, I always thought the Early Champ designs were based on the RCA tube handbooks? 

The very first ones were, but Leo soon started to evolve them quite heavily. When they got as far as things like the 5F6-A Bassman, which Marshall (accidentally badly!) copied, they were pretty much all his own work.

The Blackface amps were in many ways intended to be 'hi-fi' - or at least as close as possible given the limitations of the technology - that's why the tone stack is so scooped, to compensate for the midrange-only speaker cabs.

There are still some interesting anomalies though, like the Deluxe Reverb OT ratio being so badly mismatched... my guess being that it was originally intended to use 6L6s or perhaps something like 7591As, but they found it could be done more cheaply with 6V6s and forgot to change the ratio, or just liked the sound of it anyway. That's what is actually most responsible for the characteristic flubby overdriven sound of them, rather than the 6V6s themselves.