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Post subject: Class A/B Fender Amps and Effects Pedals.
Posted: Mon Sep 27, 2010 4:45 am
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Hi everyone, recently I have purchased a Fender Pro Tube Twin Amp.

The more I play this thing, the more I am learning about the greater depths the pedals I have in my pedal board.

As the Twin allows me to run my pedal board through the effect loop,
I have the joy of hearing what I believe to be the true tone of the pedals themselve's.

As the Twin sounds Hi Fi, I can't believe how awesome these pedals actually sound now.

What are your thoughts and experiences with effects Pedals and Class A amps used together.


Last edited by kineman karma on Mon Sep 27, 2010 5:45 am, edited 1 time in total.

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Posted: Mon Sep 27, 2010 5:10 am
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It looks like class A/B to me. 100watts into 4 ohm through 4 6l6's.
The only fender class A amp is the champ isnt it?

http://fender.com/products/search.php?partno=0215700000

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Posted: Mon Sep 27, 2010 5:44 am
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nikininja wrote:
It looks like class A/B to me. 100watts into 4 ohm through 4 6l6's.
The only fender class A amp is the champ isnt it?

http://fender.com/products/search.php?partno=0215700000


Ok good point, I will modify the title to class A/B amps.

I was under the impression that it was a Class A.. which ever class A or A/B it still kicks arse... :wink:


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Posted: Mon Sep 27, 2010 8:45 am
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nikininja wrote:
It looks like class A/B to me. 100watts into 4 ohm through 4 6l6's.
The only fender class A amp is the champ isnt it?

http://fender.com/products/search.php?partno=0215700000


That was always my understanding from my military tech school days and the class A theory that's presented in the RCA Receiving Tube handbook.

However, there are apparently more issues to be considered......

http://www.aikenamps.com/ClassA.htm

HTH

Arjay

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Post subject: Re: Class A/B Fender Amps and Effects Pedals.
Posted: Mon Sep 27, 2010 8:54 am
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What pedals are you running through the loop versus in front? And in what order? You can tweak your sound even further depending where you put your pedals.

You are hearing the "true tone" of your pedals because you have one heckuva LOUD and CLEAN (when you're not using the overdrive channel) amp. Being such a clean amp with tons of headroom means it doesn't color the sound of your guitar or effects much. In fact, if you never use the overdrive channel, you can save yourself the hassle of using the effects loop and put all the pedals in front.

Effects pedals don't care whether an amp is class A or A/B.

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Posted: Mon Sep 27, 2010 3:22 pm
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Retroverbial wrote:
nikininja wrote:
It looks like class A/B to me. 100watts into 4 ohm through 4 6l6's.
The only fender class A amp is the champ isnt it?

http://fender.com/products/search.php?partno=0215700000


That was always my understanding from my military tech school days and the class A theory that's presented in the RCA Receiving Tube handbook.

However, there are apparently more issues to be considered......

http://www.aikenamps.com/ClassA.htm

HTH

Arjay


Well well, now I am confused. I suppose without getting inside one, or being much more conversant with wiring types. I'll never know for sure. :shock:
What would you get out of a couple of 6L6's in class A push pull? About 10-13watts each?

Anyways one good link deserves another. I'm currently trying to make sense and wade my way through this lot in order to educate myself. There may be something in there of interest to you. All are public domain, no copyright issues.
http://www.pmillett.com/tecnical_books_online.htm

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Posted: Mon Sep 27, 2010 3:26 pm
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It could be Class A-A/B like the AC30. :shock: :?

Class A so far up the volume then shifts to class A/B.

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Posted: Mon Sep 27, 2010 3:50 pm
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nikininja wrote:
What would you get out of a couple of 6L6's in class A push pull? About 10-13watts each?


My RCA tube handbook says 12 watts for one 6L6 in singled-ended (presumably class A) operation. So the hypothetical 10-13 watts per for a pair seems eminently reasonable and do-able.

I remain confused about how the duty cycle is calculated given my extant knowledge about long-tail phase inverters and how such a configuration interacts with the alleged class A architecture.

(I must study this further......).

Thanks for that link, NN.

Arjay

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Post subject: Class A amps
Posted: Mon Sep 27, 2010 4:20 pm
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Here's a pretty good article about class A explanation. There is even a pdf down loadable version. :)

http://www.mesaboogie.com/US/Smith/ClassA.htm

From the article:
What Class A really means is that: “Grid bias and alternating grid voltages are such that plate current in a tube flows at all times”. Got that? That’s the entire definition from the RCA Tube Manual: the Ultimate Authority itself.

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Posted: Mon Sep 27, 2010 5:05 pm
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Thanks Nik, thanks Arjay and thanks Shimmilou,

you guys have provided some very interesting reading that opens up another element of learning for me and probably others.

Arjay I read your link posting and it was very interesting and quite easy to read for someone simple minded like myself :D

Though I did get to a point where it became mumbo jumbo but at the conclusion I had a better knowledge of what Class A and Class A/B do.

When I asked my gig at the GC I source from, he told me that the Pro Tube Twin is a Class A amp.

Up until now my initial knowledge of what is the meaning of the Class of amps was zipp...

Thanks guy's, new learning of what I possess is always fun.

I like what Nik said in another post I read though, something to the effect of " It gets to a point where everything technical doesn't matter, so just play" Please don't quote me word for word Nik.... it was something like that. I think it was in relation to a pod in andybighairs posting.. :)

:D


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Posted: Mon Sep 27, 2010 5:08 pm
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Hate to say this but Mr Smith may be wrong or intentionaly misleading. How do you get 30watts out of 4 el84's in classA?
Vox couldn't do it.
Here's a write up by a guy I know who builds very very good amps. One day I may be lucky enough to own one.
http://www.sheldonamps.com/amptalk/myths.php
He puts it in plain english. If a thicko like me can understand it, it must be plain. :lol:

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Posted: Mon Sep 27, 2010 6:44 pm
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nikininja wrote:
....How do you get 30watts out of 4 el84's in classA?
Vox couldn't do it.....


I thought that the EL84 is a 12 watt tube? 4 x 12 = 48 watts available. In class A, wouldn't the tubes idle at about 6 watts each, and output sine would vary around that idle as a mid point, varying from almost zero to 100% each? Randall Smith is quite the expert about tube amps. I can't see an advantage to him being misleading. :?

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Post subject: Class A amps
Posted: Mon Sep 27, 2010 8:04 pm
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After reading the Sheldon Amps link that you provided nn, I can see where he is confused about class A. Remember, class A only means that the output tubes are biased such that they never stop conducting current during operation. This statement in particular (among others):

"Class A amps are at the very most 50% efficient so to get say, 25W of output they have to have valves capable of dissipating at least 50W of power. It's not altogether good news for those of us who like a lot of 'Sag' in our amps but more on that later."

Yes, the class A AMPS are inefficient, not the tubes. The tubes are the same efficiency regardless of how they are biased or what class that they are run. So if you want 25 watts of power out, you only need 25 watts from the tubes. How ridiculous to say that 50 watts out of the tubes will only give you 25 watts out of the tubes. So, 25 watts is disappearing? Nonsense! Some of the power is "dissipated" as heat, but it doesn't change because of the class it's running. :? The inefficiency of the class A AMP means that the AMP needs to supply more power to the tubes than they would in a class AB amp, because none of the tubes turn off in class A and that means more power wasted by the amp. The tubes don't somehow become less efficient because they are run class A. :idea:

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Posted: Mon Sep 27, 2010 10:49 pm
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These links are all great reading and full of good info ! Arjay ,I've probably read that article 10 times, and still get something out of it each time. Nik, the Sheldon link is very good and similar to Aspen Pittman's articles on the same subject. Shimmilou, IMO you pretty much sum up the efficence quotiant. It's not just the tubes output, but how it is applied and utilized. In a Class A push-pull configuration nearly half of the wattage is sacrificed(in heat dissapation of unused output power) to produce the clear- undistorted signal. It never ceases to amaze me, how my Clubman35 was so clean at medium pick(or finger) attack, and move into a gnarly grind, when i would dig into it. Pre amp and PI influence, I guess. Art

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Posted: Mon Sep 27, 2010 11:25 pm
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aclempoppi wrote:
In a Class A push-pull configuration nearly half of the wattage is sacrificed(in heat dissapation of unused output power) to produce the clear- undistorted signal.


I'm betting that Leo discovered this and opted for class AB operation for the more powerful amps, taming the distortion by use of a NFL to produce a louder circuit (compared to a class A P-P configuration using equivalent power tubes and output trannies). As well, radiant heat would be reduced, thus extending tube life and reducing component fatigue.

It certainly makes for an interesting discussion.

Arjay

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