> From: Peter Chadwick <Peter.Chadwick@gpsemi.com>
>
> OK, I see what you mean. I made the unwarrantable assumption that one
> automatically drives the grid up to zero volts to get the most swing -
> but you don't have to, although that seems to be the recommended design
> procedure for maximum output from any particular tube in AB1.
That's right Peter. I'm sorry I didn't explain that better. A drawing
would have helped, hi.
My point was there is absolutely NO requirement the grid go positive
with respect to the cathode in ANY letter class of PA, just like
there is no restriction against grid current in any letter class of
PA. And contrary to claims, there is NO requirement peak anode
current be reached at zero grid volts. It might be reached, but it
more than likely it is not.
A 3CX3000F1 will work in AB2 just as a 3CX3000F7 will work in
AB1, or vice versa.
> I've come across commercial specs which wanted the IMD's maintained down
> to a tone spacing of 30Hz - that really canes the PSU - I'm sure that
> the three tone test that you suggest, with, I presume, two of the tones
> very close together, is a much more delicate and elegant method of test.
It works best for me when I want to test a tetrode or solid state
amp!
> The noise loading of course, does have components down to low
> frequencies. Noise testing with a notch in the noise band (and looking
> at the IM noise folded into the notch) was written up by Marconi
> Instruments some years back as a more delicate test for MCVFT signals
> over an ISB tx.
I'd love to see that paper! I was trying to follow your description
but I couldn't, so the concept escapes me. Is it something us poor
Hams can use at home?
It is great reading your posts and Ian's posts about IMD. You guys
obviously have given the subject much more thought than we have on
this side of the pond.
I hope the next tetrode article pays more attention to being a clean
design.
73, Tom W8JI
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