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[Amps] Amps] SB-220 update & gettering

Subject: [Amps] Amps] SB-220 update & gettering
From: John Lyles <>
Date: Sat, 26 Nov 2016 10:19:22 -0700
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Good to hear you found the keying circuit issue and fixed that. Would hate for that relay to only partially close while a kW of RF is trying to come through the contacts.

You don't need to see cherry red with those tubes, but in high voltage SSB setting you might see a dull orange on one or both tubes. 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. 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. Does yours have the stock input tuning on each band? I followed the techniques outlined by R. Measures years ago for mine, and de-Q'd the input on each band with a different L/C value, and got better match across the bands than stock. Using an Icom XCVR to drive it, this was a good improvement. It flattened the gain quite a bit too. I think I got about 1150 watts on 10 though.

You can determine the amount of power in the anodes, of course, by taking the key down (quickly) DC input - Ep x Ip, and the RF output and subtract these powers. The difference is roughly divided in half in each tube. I say roughly as sometimes one tube might have slightly higher mu than the other, due to mechanical variations such as grid to cathode spacing. That tube would turn on with more quiescent anode current than the other, for the same cathode bias voltage. It would likely have slightly higher RF gain as well, developing a little over half of the total power you are getting. In such instances, one tube might have more anode color.

Date: Sat, 26 Nov 2016 15:20:54 +0000 (UTC)
Quick update on the SB-220:

   After getting the HV supply working, I was still having trouble getting RF 
out.  The relay wouldn't key
via the TS-590S, and when I tried to key it by directly shorting the inputs, it 
would sometimes key and
sometimes not.  And when it did key, it didn't click very loudly and seemed 

  I figured something was wrong either with the relay or the relay keying 
circuit.  The keying circuit was easier
to fix, so I replaced the Harbach soft-key board with a new one.  I also ran a 
piece of paper between the relay
contact to clean them a bit. Now I get a solid *THUNK* when the relay keys, the 
TS-590S switches it just fine,
and it puts out between 1000 and 1500 watts out depending on band.  It works!

Now my primary question:

   Even when running a 20 minute SSB QSO yesterday at a kilowatt on the low 
voltage CW setting, the 3-500Z's
didn't appear to be cherry red.  (The inner case is closed, so they are not 
easy to see through the holes; the
outer case has not been put on yet.)

   I am a bit concerned that they aren't hot enough to getter even though they 
are putting good power out. I don't
know how long the amp was unused before I bought it.  Any thoughts on ways to 
get them a bit hotter?
Perhaps run some RTTY at 400 watts for a while?

   I am not seeing any purple glow, arcing in the tubes, or other signs of 
failure.  And the power levels I'm getting
(1400 watts on 40, 1500 watts on 80, both with 100 watts drive and SSB voltage 
setting) suggest that the tubes
are not at all soft.

   Hope everyone had a wonderful Thanksgiving, and that the bands improve soon!


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