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Ampage's Vox AC30 week...

7/12/2000 10:09 PM
Roberto Lasco
Ampage's Vox AC30 week...
Since the topic is fresh, I'd like to introduce another related question:  
Thanks to Randall Aiken, now everybody knows Ac30s are not Class A amps, right ? (?)  
But then, how do you guys see the bias question ?  
I mean, the advice was ALWAYS to use a 100% plate dissipation figure (12W) for each EL84.  
AC30s indeed came from factory near this plate dissipation limit, and do sound good as is.  
Anybody is lowering to 8W ? Or, screw the rules, let's get a "hotter than hell Class AB" amp ?  
Opinions ?  
7/13/2000 5:15 PM
Matthew Springer

All this Vox AC30 talk is making me itch to go buil done. Does anybody have photos of a homebrew?  
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7/13/2000 5:25 PM

yea just finished mine last week i still have to fix some hum but it sounds great!  
i only have one pic so far but more will be up soon ooiskramerac30.jpg  
i also want to add a master vol how do i do this?  
anyone have a schematic?
7/18/2000 12:15 AM

check the spitfire schem here on ampage for a good master volume idea.  
it is almost like the cut control, but there is no capacitor, they just mix the two out of phase signals together to cancel them out.  
7/18/2000 10:58 PM
Steve F.
Pics of my latest effort, not exactly a clone  
because it has two independent preamp  
channels, reverb, and 4 x10 cab rather than  
a 2 x 12 combo, besides, the cosmetics are  
mostly Fender inspired, (can't afford that  
diamond grille cloth) can be found at:  
it's under "AC/Whatzit" if you're interested.  
Sort of a strange brew of my favorite amp  
configurations. It came out rather well,  
my friends can't even find it within themselves  
to make fun of this one!  
The schematic is an adaptation of one I got from  
Dave Harris - I think there's a posting of Dave's  
on Steve Ahola's Blue Guitar site, if I remember  
Steve Fillipp
7/18/2000 2:41 AM
Steve A.

Thanks to Randall Aiken, now everybody knows Ac30s are not Class A amps, right? (?)  
    What I have heard from a lot of people is that they are essentially Class A at lower volumes but more like a very hot Class AB when you crank them up...  
    Labels are just labels... whether Class A or Class AB the AC30 is a great amp that uses cathode biased EL84's. Some people who have been working with configuration have concluded that if you lower the bias current too much it just doesn't sound as good. 100 ohms for two EL84's may be a little too hot, but anything over 130 ohms is starting to get too cold.  
    Has anybody tried wiring up an AC30 clone with a fixed-bias switch? Seems like you could get a more dynamic sound at high volumes using fixed-bias... (While everybody makes a big deal of the Vox amps being "Class A" perhaps it is also the absence of negative feedback that contributes to their sound...)  
Steve Ahola
7/18/2000 11:45 AM
Ray Ivers

I haven't tried the fixed-bias AC30 mod (I would if I had one, though). I did read somewhere that this mod results in a cool-running 50-watt AC30 with a really dynamic clean sound; sounds to me like something a lot of AC30 owners might like. A capacitive-coupled negative supply (or preferably a separate bias transformer and PS) would have to be added, but the rest of the job wouldn't be too hard.  
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