vox ac15 vs. fender deluxe reverb

nathan a

Senior member
Messages
1,836
Hey folks

Spent a few hours at the local shop tonight, trying out tube amps in the 15-30 watt range. My favorites, by a huge margin, were the fender deluxe reverb reissue and the vox ac15. The deluxe had this awe-inspiring clean sound (which I know isn't a surprise to you, but I'm new to tube amps). The guys kept asking me to turn down though as I tried to get the deluxe to break up.

And the vox, wow. Great clean sound, different from the deluxe (and in my opinion, not as inspiring, but still damn good). Broke up real easy and sounded absolutely freakin fierce. Honestly, I wish it had a little more clean headroom. I didn't try the version with the celestion blue speaker.

I want your opinions because I'm after one of these two amps; they both stole a piece of my heart.

If I went the deluxe route, I'll be getting my overdrive from a pedal, which is okay because I often don't use much dirt at all. But sometimes I really like the 'mildy dirt amp + overdrive pedal' sound.

If I went with the vox, do you think I should go for the celestion blue speaker option? It's an extra $350; should I just get the stock speaker model, and replace it myself later? Also, I'd consider (not certain at all) changing the tubes. Still el84s, but just a higher rating. At this point, sounds like a lot of work for a brand new amp. But it's overdriven tone was to DIE for.

Thoughts?
 

Kostas

Senior member
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1,381
nathan a said:
If I went with the vox, do you think I should go for the celestion blue speaker option?
Definitely. It's a magical speaker, highlights the sound of the Vox. The Deluxe breaks up on very high setting, I would say probably after 8 but it's too loud for home enviroment. The most transparent pedal I have heard is BB Preamp, if you don't need too much gain it's an awesome pedal.
 

vic108

Senior member
Messages
307
Save up and get both.

Two different animals - but both great amps.

If you have limited funds, try the Vox Valtronix series.....
 

nathan a

Senior member
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1,836
They are such different beasts, and to get both is amazingly tempting. But I just don't think I can justify that sort of spending right now. Maybe in a few years, but not now.

If I go for the AC15, it'll be with the celestion, thanks kostas.

The only amps I've ever owned are Marshall solid states in various wattages (15, 25, 100.. completely pointless). I guess it wouldn't hurt to play through the valvetronix modeling amps, but I'm really wanting just straight up tube.
 

Phrygian

Senior member
Messages
459
Cathode biased vs fixed bias.  I personally prefer the compressed clean sound of the blackface circuitry when it's cranked, but you'll hit a wall where they almost instantly go full on distortion (which can be ugly sounding).  The cathode biased amps have a more gradual break up.  Actually, it has more to do with the combination of the negative feedback loop, biasing method, and plate voltage.  As others have said, they're different animals.
 

-CB-

Senior member
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5,427
I'm sorry....

but it has nothing to do with Cathode Bias vs Fixed (Grid) Bias.  Nothing at all.

The AC15 is a class A design.  It is also cathode biased.  Amplifiers of Class A design can be cathode biased, simply because the current draw of a tube running in class A is rather uniform, showing almost no variation with signal strength - because the tube must conduct the full 360 degrees of the waveform.

The Deluxe Reverb is a fixed grid bias design... but really, the why is more important than the what.  IOW, its a Class A/B amplifier (we'll skip the AB1 or AB2 varieties right now).  As such, if it was cathode biased, we'd see the bias relationship between cathode and grid radically change as the current went up during strong signal presence (ohms law, I/R drop).  You simply cannot cathode bias a Class A/B design and have it work right.  Not that you might not "like" the tone (subjective) but it wont work as it should, will lose a lot of power, have considerable unnatural sag and generally be a one trick pony.

The thing is, they're just different designs, and thats that.
 

shaneman

Active member
Messages
80
WOW.  I'm gonna read that last post a few more times.  CB is a Jedi.  I've been curious about that AC15w/the Blue.  You gotta go and check that one out.  I'm gonna wait until I've got the cash.  I absolutely hate going to check out gear and not being able to buy it right then and there. 

Later,

Shane (oh, and may the force be with you. :headbang1:)
 

Phrygian

Senior member
Messages
459
-CB- said:
I'm sorry....

but it has nothing to do with Cathode Bias vs Fixed (Grid) Bias.  Nothing at all.

The AC15 is a class A design.  It is also cathode biased.  Amplifiers of Class A design can be cathode biased, simply because the current draw of a tube running in class A is rather uniform, showing almost no variation with signal strength - because the tube must conduct the full 360 degrees of the waveform.

The Deluxe Reverb is a fixed grid bias design... but really, the why is more important than the what.  IOW, its a Class A/B amplifier (we'll skip the AB1 or AB2 varieties right now).  As such, if it was cathode biased, we'd see the bias relationship between cathode and grid radically change as the current went up during strong signal presence (ohms law, I/R drop).  You simply cannot cathode bias a Class A/B design and have it work right.  Not that you might not "like" the tone (subjective) but it wont work as it should, will lose a lot of power, have considerable unnatural sag and generally be a one trick pony.

The thing is, they're just different designs, and thats that.

I still think plate voltage and the feedback loop play a significant role in the response and character of the amp.  I'm not at all familiar with Vox circuitry.  I know that Fender and ultimately CBS during the 60's were shooting for efficiency (which unfortunately during the CBS era led to the use of ultra-linear transformers).
 

-CB-

Senior member
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5,427
Again.... not on a class A design.  Class A is a design that uses nearly continuously even current.  As such, the "sag" and vocal effects of a tube rectifier are lost in that design.

In the Deluxe Reverb.... the older ones (or any really...but spec'd in the older ones), they used a GZ34, vs the 5U4GB in the later models.  The GZ34 will sag "just a little" in a DR, but not much.  The 5U4GB doesn't sag at all.

However, in amps of slightly greater power - 35 to 50 watts, the tube rectifiers shine.  The problem is - low powered amps are all Class A, and medium powered amps dont pull enuf current to get the rectifier mojo goin (that much).  Bigger amps to about 50w do it mo'betta.  Larger than that, you cant rectify via tube unles you jump thru hoops (two tubes, protection, mondo transformer, etc)
 

nathan a

Senior member
Messages
1,836
-CB- said:
Again.... not on a class A design.  Class A is a design that uses nearly continuously even current.  As such, the "sag" and vocal effects of a tube rectifier are lost in that design.

In the Deluxe Reverb.... the older ones (or any really...but spec'd in the older ones), they used a GZ34, vs the 5U4GB in the later models.  The GZ34 will sag "just a little" in a DR, but not much.  The 5U4GB doesn't sag at all.

However, in amps of slightly greater power - 35 to 50 watts, the tube rectifiers shine.  The problem is - low powered amps are all Class A, and medium powered amps dont pull enuf current to get the rectifier mojo goin (that much).  Bigger amps to about 50w do it mo'betta.  Larger than that, you cant rectify via tube unles you jump thru hoops (two tubes, protection, mondo transformer, etc)

Can you explain what you mean by sag? Also what's a rectifier and what does it do? And how is it also a verb? I know nothing about amplifier circuitry beyond what types of tubes are used.
 

-CB-

Senior member
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5,427
Sag is often mis-described. 

The "what" of sag is the pronounced variation in the envelope of a note, as its picked, and decays.  It has the influence of both dynamic attenuation of amplitude as well as bandwidth, or freq. response, of the note.  A compressor with a bit of subtle wah, is one way to think of it.  Maybe reverse wah... more of a awwwwh tone.

The "how" is often told as a decrease in the B+ and this is the case.  However, its not the decrease in B+ that is really the cause of the audio effect.  What really does it, is that the decrease in B+ screws up the bias relationship, and throws the whole curve of the tube out the passenger side window...  IOW, properly biased, the decrease in B+ would have a little, but subtle effect.  But when the bias remains more or less fixed, the relationship of cathode to grid to plates (and screen grids) is dramatically altered.  Its this altering of relationship, not solely reduced voltage on the plates that makes that tone.

If you want to hear sag, try a 50's Deluxe Amp (5E3), or a 5E6 (not 5F6) Bassman
 

Phrygian

Senior member
Messages
459
You're going to have me re-researching this stuff again.  :)  It's been a while since I've immersed myself in tube amp circuitry.  I've never really considered the A vs AB debate seriously, just cathode vs fixed bias.  For those that don't know, this has to do how the waveform cycle is handled by a push-pull power amp.  Class AB amps sacrifice some crossover distortion for efficiency... not a good/warm kind of distortion (by most standards).

My Princeton Reverb probably has one of the worst designed split-load phase inverters ever, and I still think it sounds great.
 

jackthehack

Senior member
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5,630
CB - You lost everyone on thread 2 posts ago... Ask them for their favorite 100 watt Class A amp design...
 

nathan a

Senior member
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1,836
I appreciate the explanation, even though I have no idea what you're talking about. The fault is probably in my brain, not your explanation. I understand the sound of the 'sag' you're talking about though, I think.

But, uh, so it's the deluxe that sags? Or not anymore... right? So neither of them..? F--- it, I'm just gonna have to close my eyes and see which amp sounds better. Too much talk for me.
 

-CB-

Senior member
Messages
5,427
A deluxe reberb will have more sag than an AC15

The AC15 will ... probaby break up more, and sooner, but for other factors.

Part of the breakup tone - is the valve hitting its top supply rail, and that will compress things too (and nice and softly) but thats different from sag.  WHen the signal hits the supply rail - the tube is at saturation - clipping, soft clipping, and thats "the tube tone" we love.
 
G

guitlouie

Guest
I played with this Maven Peel Ganesha head at the local botique,  it has a "sag control".  This was one bad ass amplifier, went from way old school to the best of the newer breed.........Then the guy realized there was no way I was going to buy it and politely asked me to get the hell out!!!
 

-CB-

Senior member
Messages
5,427
Just for that go back, ask to see the amp, and play "Stairway to Heaven" followed by "Smoke on the Water".


Was tellin' Vic the other day, if I ever get some terminal disease, just lock me in a room with a box of razor blades and Smoke on the Water playing non-stop. 
 
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