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maartentje 20th February 2008 07:54 PM

Schematic: Audio Innovations, The first audio amplifier
Hai there,

Is there anybody with a schematic of the Audio innovations - The first audio amplifier? Or service manual?

*12watts pure class A PP
*2A3 tubes


flyinglemur 20th February 2008 09:33 PM

AFAIK there can't be Class A p-p

gingertube 20th February 2008 11:07 PM

There certainly can be full Class A Push Pull.

It simply means that neither tube ever runs into cutoff. As soon as one tube cuts off then thats Class AB.

When one tube cuts off then the effective load seen by the other tube changes from Raa/2 to Raa/4 and it is handling this transistion from class A into Class B that is the one of the major "bug-bears" of Class AB design. Ultralinear Outputs seem to handle this transistion a little better than pentode mode.

There are actually a lot of pure Class A Push Pull Amps out there, particularly with Triode Output.

Then there are also quite a few that claim to be pure Class A but aren't.
In the Guitar Amp world the classic example is the VOX AC30 which was claimed to be full Class A but is'nt.

One of the measures of a good Class AB Amp is actually how much Class A power it can deliver before the transistion into Class B occurs - generally the more the better. This will depend upon the idle current in the output tubes. With higher idle current you can swinf more signal current before a tube runs into cut off, that is more Class A power.

Take that to its obvious conclusion and you see that pure Class A push pull should be much better than Class AB.



I don't know if this is the amp you were looking for. Its a parallel 2A3 Push Pull Class A

flyinglemur 21st February 2008 08:32 AM

Thanks for that :D

maartentje 23rd February 2008 12:01 AM

Hi there,

thanks for response. But thats not the orginal schematic. The orginal audio innovation use only two 2a3's per channel.

Somebody else maybe with schematic?

Best regards

maartentje 16th April 2008 10:25 AM


ErikdeBest 17th April 2008 10:57 AM

I am curious as how the amplifier extracts 12W from two 2A3 valves...


Geek 17th April 2008 11:06 AM

Hi Erik,


Originally posted by ErikdeBest
I am curious as how the amplifier extracts 12W from two 2A3 valves...


Easy :)


"....allows us to drive them at full Class A Push/Pull power levels...."

ben goh 17th April 2008 11:19 AM


Try this

revintage 17th April 2008 11:36 AM

It is possible to squeeze out 12W in class-AB. But not in Class-A if you want to stay below Pamax.

To call the Straub 12W class-A is as wrong as to call the famous Vox AC-30 30W class-A.

But I must say the Straub concept looks nice!

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