I found an article on AC30s today at work

thermionic

Waiting for something to print out, I had a flick through some science/engineering magazines we have in a rack (this counts as Continuing Professional Development for me, ha ha!) I found an article about the Vox AC30, and how the design and manufacture had changed with the times. Turned out to be a bit disappointing really, but I thought I'd leave it here for the AC30 fans to have a quick read.

Vox AC30 - Eureka Magazine

Cirrus

Presume the pictured amp just happens to be the brand new, very expensive, limited run UK made AC60-whatever-they're-calling-them...

ICBM

I'll give them credit for not using the c-word . I think that's the first time I've ever seen an article about the AC30 which doesn't.

They call it "cathode biased ... push pull ... high bias condition", which is correct!

ToneControl

ICBM said:

I'll give them credit for not using the c-word . I think that's the first time I've ever seen an article about the AC30 which doesn't.

They call it "cathode biased ... push pull ... high bias condition", which is correct!

you mean "Class A"?

ICBM

ToneControl said:

you mean "Class A"?

Exactly .

Probably the most over-used and inaccurate piece of marketing nonsense in the whole jargon of guitar amps…. maybe even more than "point-to-point".

The characteristic compression and 'chime' of an AC30 is specifically because it's a cathode-biased Class AB amp and *not* Class A.

So full marks to an article which does mention a tiny bit of technical detail, but avoids repeating the usual fallacy.

RiftAmps

@ICBM yes, praise that author, he did good!

My favourite 'not-incorrect' description of an AC30 was "it runs in conditions similar to Class A" - always thought that was a neat way of getting around it

jpfamps

ICBM said:

ToneControl said:

you mean "Class A"?

Exactly .

Probably the most over-used and inaccurate piece of marketing nonsense in the whole jargon of guitar amps…. maybe even more than "point-to-point".

The characteristic compression and 'chime' of an AC30 is specifically because it's a cathode-biased Class AB amp and *not* Class A.

So full marks to an article which does mention a tiny bit of technical detail, but avoids repeating the usual fallacy.

Running open loop is also a significant contributing factor to the "chime" (as are the Celestion Blues.).

ICBM

jpfamps said:

Running open loop is also a significant contributing factor to the "chime" (as are the Celestion Blues.).

Yes - and lack of NFB is also sometimes claimed as a characteristic of Class A too!

The AC30/Blue thing is interesting - I don't know of any other amp/speaker combination which is quite as finely tuned as it, in the sense that AC30s don't sound quite as good with any other speakers and Blues don't sound quite as good with any other amp.

thermionic

I really need to get some 10" Blue equivalents in my AC15. When I owned a battered AC30, it had G12-80s in it, which partly explained why it didn't sound much like a typical AC30.

impmann

ICBM said:

jpfamps said:

Running open loop is also a significant contributing factor to the "chime" (as are the Celestion Blues.).

Yes - and lack of NFB is also sometimes claimed as a characteristic of Class A too!

The AC30/Blue thing is interesting - I don't know of any other amp/speaker combination which is quite as finely tuned as it, in the sense that AC30s don't sound quite as good with any other speakers and Blues don't sound quite as good with any other amp.

Funny... I preferred them with greenbacks, back in the day.

AlexC

I think many of the famous players who've used AC30s have probably also used Class As...