Re: {Collins} Tuning the 30L-1



Hi Rick.....
I think most everyone would agree to ignore the Collins 'zero tune' method.
Even if calibrated the meter ckt reacts differently on each band so it is
unreliable to use.
I don't think it is necessary to check any components.....just use a
wattmeter and tune it  your way.
With 811A tubes I would set the load to about 2.5 then drive to 300ma and
quickly dip the plate, then drive harder and load to 600ma.
The load control will vary with the band and load.
For 80mtrs my load control is 3.5.
My amps have Svetlana 572B tubes and the YK power supply replacement board.
I load my amps to 300ma then drive and load to 800ma max while observing the
watt meter.



73

David Harmon
K6XYZ
Sperry, OK

-----Original Message-----
From: Collins [mailto:collins-bounces+k6xyz=sbcglobal.net@xxxxxxxxxxxxx] On
Behalf Of Rick Poole WA1RKT
Sent: Saturday, November 1, 2014 3:58 PM
To: collins
Subject: {Collins} Tuning the 30L-1

I have two 30L-1 RE amps that have been in use for a couple of years, one
driven by a KWM-2A and the other by a Heathkit Marauder.

I have never had any meaningful success following the process in the manual
for tuning.  Instead I have had good luck tuning for maximum output while
keeping the output at or below 700 watts PEP and paying close attention to
the duty cycle to keep from stressing the tubes.  Then I increase the
loading a notch or so to hopefully keep the grid current under control (gee,
thanks, Art, for the grid current meter... NOT...), re-peak the tuning and
there they sit.  Load control usually ends up between 3 and 4.  Both amps
seem happy with that.

The "Tune" meter is nowhere near zero when I finish... usually it's around
.1 or .2 below zero.

Tuning duty cycle is:  10 seconds on and 20 seconds off, repeated three
times, then a full minute off, lather, rinse, repeat... although usually the
amp is tuned before the end of the second 10-20 cycle.

I had one of the amps (with four older RF Parts 811A tubes) on the bench for
some unrelated work, and connected it to a dummy load and peak-reading
SWR/power meters on both input and output.  Tried the "book" way of tuning
and was able to get only about 400 watts peak out with 100 watts peak drive,
the Load control ended up at about 9, and the tube plates would start to
turn color within just a few seconds.  I didn't dare leave it on long enough
to check the plate current but I'm sure it was very high.

Reverted to "my" way and got 650 watts peak out with 80 watts peak drive and
600 ma plate current, the Load control ended up at about 3, and the tube
plates stayed black for the full 10 seconds (didn't try it for longer than
that).  SWR was 1:1 at the amp's output (to the dummy load) and 1.1:1 at the
amp's input.

My question is... why are the "book" method results so obviously far away
from anything reasonable?  Do I need to go through all the components to the
left of the tubes in the schematic, and check them for value?  Is that
circuit a common failure point in these amps?

Rick WA1RKT
Londonderry, NH
Catch me on 14.300 MHz Intercon / MMSN most days
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