[AMPS] Amp Tuning (was 3-500Z Grid Current Rating)

[Dick Green]

> I've found with my Henry that using the old "dip and load" technique
always
> leads to the best operating condx

snip...

> With modern gear there sometimes is a tendency to simply tune for max
output without paying
> close attention to the grid/plate.

snip...

Thanks, Dave. I'm glad somebody finally said this. I've seen a lot of posts
here about tuning for max output, and I've never been able to reconcile that
approach with the old "dip and load" technique I learned with my first tube
transmitters back 15-16 years ago.

These days, I use a hybrid approach with my SB-220. I have an external power
meter positioned on top of the amp case, very close to the fixed Ip meter
and multimeter, and I set the multimeter to Ig. That way, I can see power
output, Ip and Ig at the same time. After setting the drive level, I dip the
plate (making sure output peaks as well), advance the load control for max
output, and repeat until there is no further increase in output. While doing
all this, I keep one eye on Ig to make sure it stays within safe limits,
reducing drive and retuning when Ig is too high. After this, when operating
SSB, I try to remember to advance the load control slightly for improved
linearity, dropping output maybe 5% (recommended by KM1H.)

This only applies to the first time I tune the amp for a given antenna and
band combination. After I do the initial tuning, I label the positions of
the Tune and Load knobs. To QSY, I set the band switch and move the
Tune/Load controls to the marked presets. Then I key the rig, dip the plate,
adjust the load back and forth over a small range to find the sweet spot
where output peaks, then advance the load for best linearity.

Even though this works well, I still have a couple of questions:

For example, when doing the initial tuning, I first tune the amp at a lower
drive power (half or less of what it will take to drive maximum power), then
I retune at full drive power. I do this mainly to preposition the Tune and
Load controls to the approximate region where they  will be when tuning for
max rated output My thinking is that hitting the amp with full drive power
when the controls are at more or less random positions is a bad idea and may
cause arcing. Is this the right procedure or is there a better way?

Second, after increasing the Load control for best linearity, should the
plate be redipped?

73, Dick, WC1M



--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm