[John Byrns]

In article ,
(Don Pearce) wrote:

On Thu, 25 Oct 2007 13:43:56 GMT, John Byrns
wrote:

In article ,
(Don Pearce) wrote:

Can you overdrive a class A amp to cutoff?

Yes, it is painfully easy.

In my experience what
happens when you overdrive a class A amp is that one device saturates,
and the other sticks with its normal bias condition.

No, the coupling capacitor charges up as a result of grid current
shifting the bias point so that cutoff becomes even easier.

There is no
circumstance in which I have ever managed to put a class A amplifier
output device into cutoff.

You haven't tried very hard then.


The designs I have used must have been better matched in drive level
between the driver and output stages. They tended to limit almost
simultaneously so that the drive level to the output stage did not go
on rising as the input signal increased, just squared off. As I say, I
never saw an output valve go into cutoff.

That sounds like a dangerous way to go, I would think that running the
drivers that close to "limiting" would create a lot of distortion in the
driver stage before the output stage starts clipping. I think Patrick
just posted, expressing his dislike for this sort of wimpy driver.


Regards,

John Byrns

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