[Amps] Re: Amps Digest, Vol 12, Issue 59

[gw4dgu at blaenffos.org]

> **  The grid does not and can not draw current when a competent
operator........

Oh yes it can....! If you can show me a transceiver with an ALC loop which
doesn't transiently produce output spikes significantly in excess of the
steady-state level, then I'd be prepared to believe that control theory is a
form of magic.

A competent operator can certainly set-up the output of a transceiver to
keep out of indicated grid current in the steady state, but in the real
world with typical ssb transmitters, that's a highly simplistic view.

For excellent linearity, a tetrode linear amplifier of any size really does
need stable, low impedance supplies for G1 and G2. It doesn't need a higher
degree in thermionic electronics to understand why. In a class-AB1 tube
amplifier, the dc currents flowing in both the G1 and G2 circuits are
powerful diagnostic tools, providing the supply voltages are stable.

Just because Collins used a number of short-cuts in their transmitter
designs of the the '50s and '60s, it doesn't necessarily mean that we should
follow their practices slavishly half a century on. It's now possible to
make good G1 and G2 power supplies for a few tens of euros/dollars, and
these have effctively obsoleted earlier practice.


Vy 73 es Blwyddyn Newydd Dda/Happy New Year

Chris
GW4DGU