>Ditto for
> his decision to ignore Jenning's advice on using vac. relay speedup
> circuits. Switching operating bias to non-linear levels during soft
> syllables is another example.
I believe ETO incorporated the vacuum relay accelerator circuit at the
introduction of their Alpha 77 (not Dx/Sx) in 1973 or thereabout. The
circuit uses a series of diodes and electrolytic capacitors to achieve
better contact start speed for the purpose of eliminating RF hot-switching.
This is the circuit I presently use on my Alpha 70V (together with a KC-1
vacuum relay) and it does a remarkably good job with QSK at least up to my
CW limit (~35 WPM) and the exciter's waveform integrity is perfectly
maintained, as evidenced on my Bird RF sample/Scope...and I can still hear
the receiver in between character elements.
Then, somewhere in the 77Dx series, a more advanced sequencing circuit which
samples input RF and makes it pretty much impossible to hot-switch no matter
what.
Regarding the EBS, I detect a slight trace of audio distortion at very power
levels when the tube bias changes and unless the signal is +40 dB over S9 or
better, I'm not sure how much of a problem this is as a practical matter.
On my 77Dx, it's possible to adjust the grid current idle and this seems to
help.
-Paul, W9AC
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|