[Amps] SB-220 update & gettering

[Jim Thomson]

Date: Tue, 29 Nov 2016 01:16:23 +0000 (UTC)
From: Catherine James <catherine.james at att.net>
To: <amps at contesting.com>,  <jtml at vla.com>
Subject: Re: [Amps] Amps] SB-220 update & gettering


I found that at full power, 1200-1300 watts CW, I get to a dull red/orange on the bottom half of the plates.
I won't be routinely running at that power output, however.  I'm aiming for 800-900 watts CW and about
a kilowatt on SSB.  On 40 meters, about 60 watts drive and SSB plate voltage setting gives a kilowatt SSB PEP.

> If you are getting 1400 watts on 40, those tubes are fine and the vacuum pressure
> is very good. I would recommend not worrying about getter activation, it is apparently doing its job - FB.

I made more precise power measurements on 40 and 80 tonight.  In CW exciter mode, SSB switch
set to high power, 100 watts drive on 40 meters gives me 650 mA plate current, 2800 volts plate, which
works out to about 1250 watts both on the meter and calculated (assuming 66% efficiency).  On 80
meters, I get 750 mA plate current and 2700 plate voltage, which works out to about 1300 watts.
And that does give me the dull orange glow!

> BTW, what sort of power do you see on 10 meters with that amplifier. This starts to show the
> effects of losses  in the output network, and in the parasitic suppressors on the anode connections.

On 10 meters, I took it up to 60 watts drive and got about 500 watts out.  At that point, the tubes were glowing brightly,
brighter than they did at 1300 watts on 40 meters, so I chose not to take it up any higher.  My guess is that it would
peak about 700 watts, maybe a tad higher.

I will seldom if ever operate on 10 with an amplifier.  Mostly I use one on 20, 40, and 80 meters SSB for rag chewing,
on CW for DX, and I also operate on 30 meters without one.  Most of my domestic CW is at 50 watts, and if the bands
cooperate I don't need more. I don't find the high bands very useful at this point in the cycle, especially since I am not
retired and not home when the sun is up and the day bands are open.  My typical operating time is around 8 - 10 PM.

##  I would be careful about running an SB-220 at 1300 watts out on CW.  It only has a 500 va xfmr in it.  Operate
it in the CW low B+ position  at aprx 650 watts out.  The sb-220 was designed around the old rules, like  650 out on cw
and 1200 w pep out on ssb.

##  The LC ratios in the SB-220 tuned input are not optimum, the Q is way too low.  The C1 + C2 caps need to be much 
larger, and the coil needs to be smaller. 

Jim  VE7RF