Swaziland is covered

WJ2O at aol.com WJ2O at aol.com
Tue Oct 8 17:08:21 EDT 1996

Two different operations in 3DA for CQ WW SSB!

Much to my dismay, there are going to be two different Multi-Single entries
from Swaziland for CQ WW SSB.  The callsigns will be 3DA0DX and 3DA0NX.  Good
thing this isn't a CW test.  Try not to get them confused.

Our group is 3DA0DX which includes me and a couple of ZS hams.  QSL via WJ2O.

The other group is 3DA0NX which includes a couple of JA's and DL's.  QSL
direct to:
  Koji Tahara, JM1CAX, ZS6CAX
  Japan Embassy
  P.O. Box 11434
  Brooklyn 0011
  South Africa

Outside the test many of us have various 3DA0 calls.  Both operations are all
band high power and yagi's on 10/15/20.  If you still need Swaziland for DXCC
and don't get them that weekend, you weren't on.

One cool note that I just learned today.  I booked my flight through American
Airlines (so I can get my freq. flyer miles) on a South Africian Airlines
flight.  When I picked up my ticket today I found I'm in seat 15A which is
the upper deck business class on a 747.  I was bumped from coach for free!
 This is about a $1,000 upgrade!  Too bad comming back I'm still in coach.
 I'll be spoiled by then.

73, Dave, WJ2O (3DA0CQ)

>From n4zr at contesting.com (Pete Smith)  Tue Oct  8 21:47:13 1996
From: n4zr at contesting.com (Pete Smith) (Pete Smith)
Date: Tue, 8 Oct 1996 13:47:13 -0700
Subject: SB-220 10-meter output (summary-long)
Message-ID: <199610082047.NAA04186 at dfw-ix6.ix.netcom.com>

Lots of response on this one, but, unfortunately, no conclusive answer.
Nevertheless, given how many of the things thee are out in radio-land, I
thought a summaryn would be worthwhile.

A number of people reported low power output on 10, though not generally as
low as mine (700W).

A number of others reported 10-meter output within a hundred watts or so of
the other bands.

Those with low output generally suspected output tank circuit design, input
tank SWR, soft tubes,or (in one case) the Measures parasitic suppression.
My input SWR is fine, and I still don't know whether this amp has the
Measures suppressors or not (other people reported no impact on output from
the Measures units).  I'm not eager to start messing with the tank circuit
until next summer (maybe).  The cost of replacement tubes is a big
deterrent, particularly if it's a maybe...

One observation -- the widely-variant output numbers reported with
unmodified SB-220s have me doubting measurement accuracy.  I've discovered
that my Heath HM-102 tracks closely with the output measurements from my
TS-930 into very low SWRs - say 1.2 or less.  But with any sort of higher
SWR, the power output indication gets artificially high.  As someone
suggested, you really need a flat dummy load and a Bird wattmeter or
equivalent to be sure.

Thanks to the following (in no particular order):


Original query:

I've just acquired my first amp in 40 years of contesting, an SB-220.  It
shows excellent power out on 80-15 meters -- ca. 1200 W -- but only about
700 on 10.  Is this to be expected?  I remember reading somewhere that the
Measures parasitic suppressors with the nichrome wire could have this effect
on 10.  Possible?

Excerpted replies:

... Common result on most commercial amps for  the reason that
the output capacitance of a pair of 3-500 bottles is too high to allow
a decent 'Q' on 28 mHz. Actually - it can be done, but not with
air variable caps. If you pick a reasonable Q of 12-13, the capacitance
required is already exceeded by the bottles in the circuit.
A couple of the more expensive amps use neat little trix like putting
a second cap in series with the air variable, or by putting an
inductor between the plate and the cap, thereby lowering the amount of
impedance change required by the tank circuit.

...The Measures stuff is absolutely unnecessary, and will hurt ten meter
The only thing you need to do is ground the grids directly to ground lugs at
each grid pin (very short leads, no capacitors or chokes or resistors).

Then put the original style suppressors back in, but remember the resistors
need to carbon composition...not carbon or carbon film types. ONLY Allen
Bradly makes them, and they are special order.

I have some here.

That will get your 220 working like it should.

...  I remember reading in QST about the need to add abt 5pf across the 10
meter coil L1 in parallel with c33-c34. You then had to tune the coil slug
for minimum swr between the amp and the rig with a dummy load on the amp.
There were several WARNINGS and CAUTIONS about the proper way of making the
slug adjustment re: discharging the HV and not turning on amp with the top
cover removed.
High swr between the rig and amp will cause low output. I had to lengthen
the patch between my C Line and the amp to get mine to play on 10.

... Yes, it's possible that the output on 10 meters is lower than the other
bands.  That is also true of my Drake L4B which is a real blockbuster of
an amplifier even if it is getting a bit long in the tooth.

... Well, it sounds a little low on all bands. First, are you using a Bird
43 with
5000 Watt slug? The mid scale is 1500 Watts and the most accurate place
on the meter.

My SB220's that I had could get with 100 W drive was 1500 W on all bands,
even 10 M. I did tweek the input tuning, so check your SWR on the input
once you are all tuned up.

And speaking of tuning it up...... With reduced drive, tune in the normal
dip and load, then increase your drive (100 W radios, go for it) and tune the
plate and load for maximum output in the SSB mode. You do not use the CW
mode, as that was for the old days of 1 KW power limits. Leave it in the SSB
position. You should get your 1500 W out on everything, except maybe 10
meters, that should be 1300-1400 Watts, easily.

Opps! I forgot, I had the Rich Measures modifications in mine, also.

... That's about what ours does at [] - actually less than 700 on 10m,
not sure what the real reason is.  The TS830 that drives it only manages
50w on 10m, vs 100 on the other bands.   Just old technology perhaps,
30 MHz is "high frequency" stuff ---

... my SB-240 (beta model, never released to manufacturing,
twin 3-500Z) shows a little higher output, but the same relative roll-off on
10.  I've never really tried to determine why, though.

Would appreciate your post to the reflector if you get an answer, though!

... That's about all mine ever put out.  It's probably due to the
design of the pi-network, but I never tried to make any improvement.
Mine had a 160M mod installed with new coils in the pi-net, with same low
output on 10M...

... I have had one since 1978, Pete, and get about the same power out on 10
as the other bands (around 12-1300W).  I did the parasitics, but not the
AG6K mod.

... Yep, Pete, mine did same on 10meters.  Don't know why.  Mine was totally
factory specs, build with love by me.  Sorry I sold it, but then I ended
up with a Alpha 87A (after a stint with an 76PA three holer)  

... Hi Pete ... I have 'fixed' a few of my friends 220's over the years
with LOW 10m output ... Check out the INPUT SWR on the tuned input
from the rig to the amp ... We had to adjust a couple to get 10m
output to more like 900-1100 watts with 100-120w of drive ... Worst
case I recall was abt a 2.3:1 on 10m INPUT SWR, the other bands were
1.5 or less ...

... There used to be a little book of Mods for the 220 which had a mod for
10m power output.  I know it involved a 5pf cap in the tank I believe.
It had to be soldered onto the ceramic band change switch.  Also call
Harbauch  (he sells all kinds of toys for the 220), you will find him in
the mags usually in the classifieds.  If you cant find him let me know,
I can dig out some lit from him in the shack outside.

... Pete, I had an SB221 that I built from a kit and it had numerous power
mods and was lovingly built. I only was able to get 900 out with careful
I have heard that you could optimize the input network. Check input SWR on 10
and if need be adjust network components for  good 50 ohm input.
On the other hand-when 10 is open- how much power do you need ??
(tounge in cheek!)

... The SB220 is a fine amplifier and you will enjoy it greatly.  I would not do
anything with the parasitic suppressors.  The only thing I would do would be
to take the grid circutry out and ground the grids directly to the chasis
using heavy gauge copper wire or flat wire.  The modifications you are
looking concern arcing in the unit.  SB220s have a tendency to arc in the
pi-network circutry.  There has been a lot of discussion about that here on
the reflector, about what causes the arc.  The pararsitic kit claims to stop
the arc.  There are a lot of hard feelings over the whole issue and I don't
want to start another war here.  I found that the arc can be stopped by
removing the grid circutry and grounding the grids directly to the
chassis...and...loading the the amplifier properly.  The arcing is usually
caused by light loading and just a tweak of loading to the heavy side stops
the arcing.

Now, for your question.  The issue of lower power output in 10 meters is due
to the tubes.  They might be a little soft up on ten meters.  I've had that
experience too and most 220s do not get full rated output power on 10
meters.  I would say that 700 watts output is typical of the genre of amps.

... I have had an SB220 for many years and the output is less on 10 but
certainly not that dramatic. Maybe you have weak tubes. (The ones from
RF Electronics are a lot cheaper and the pair I got work fine.

...            Also I have a SB-220, I get +/- 900 watts in 10 meter, making
the conexion to the 10 meter coil more shorts, and also I changed the HV
transformer for a new Peter Dahl, but I very aprecited  if you could
forward me all the responses.

... I get 600 (cw)- 800 (ssb) outta my SB-221 on 10 meters. 200- 400 watts
less than other bands. Tuning is a little sharp, and I hve smoked the
input coil by over driving it on ten. Otherwise it's a real workhorse.
Gud luk with yours.

... I have owned several SB220, before I could afford Alphas, and I
do remember that I got nearly, but not quite equal the output on
10 meters that I was seeing on the other bands.  I don't think
700 watts versus 1200 watts is typical.  As I remember,
if I saw 1KW at 20 meters, I would see 950 watts or so
on 10.

So there you have it.


73, Pete Smith N4ZR
n4zr at contesting.com 
... and not changing!

More information about the CQ-Contest mailing list