[AMPS] tuning and such

[Tom Rauch (W8JI)]

Pete Soper wrote:
> 
> Hi Tom,
> 
> > Then you are splattering, and overdriving the tube. You should
NEVER
> > see
> > rated grid current, or near rated grid current, on SSB with voice
> > modulation. Typically the VOICE gridcurrent is 1/7th to 1/3 the
CW
> > value.
> 
> Peak or average? I think my average grid current with SSB could
have easily
> been 1/7th to 1/3 the current present during tuning on CW.

Doesn't matter, the meter never reads peak current except with a
sustained tone or carrier. Anything you see is an average, unless you
drive the meter with a peak storage circuit or hold a steady tone on
for
a second or two. Voice has multiple tones present at the same time so
voice never gives peak current.
 
>It's the momentary
> voice peaks I was asking about. The AL1200's owner told me to not
let the meter
> ever pass 150ma, period, no matter how briefly. Correct me if I'm
wrong but
> isn't 150ma well below the rating of the tube?

400 mA is the dissipation limit in that particular circuit, 300 mA is
maximum recommended, and 250 mA is typical for normal operation.

> The manual talks about a limit
> during tuning of 250ma.

To prevent arcing if the anode is severly underloaded during tuning.
 
> The day before the contest I spent quite a while with two guys
listening to
> my signal as I explored different settings. They never heard
anything but
> clear audio with a greater or lesser amount of "punch".

Anyone who can "hear" the difference in audio on the desired
frequency,
and tell if the PA is mistuned deserves a Grammy award. Even class C
amplifiers can "sound" perfectly clear with good audio on the
operating
frequency. In many cases splatter can't even be detected OFF
frequency
because of noise and QRM that masks the splatter unless the offending
ststion is very loud, or the adjacent channel is clear.

> But I'll assume that any significant boost of grid current with
processor
> usage means something bad is happening. A pity, as this means the
FT990's
> processing can't be used. I wonder why they put that feature in the
radio?

I never said that. What I said is this:

If you tune a PA on CW to a given amount of grid current, and grid
current approaches or reaches that value during voice modulation (not
during a whistle of course, a whistle is a single tone unless you are
humming while whistling, hi) the amplifier is almost certainly being
overdriven. Higher current during processing is normal, the same
current
is too much for sure. Even half the CW grid current is probably too
much
unless the processing level is very high.

73 Tom



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