I also have a nice SB-220 amplifier that I recently purchased as I
owned it when it was new. Back then, I'd had a problem with one of the original
eimac 3-500Z tubes going south. At the time, I also had a drake L-4B amplifier
and noticed that in the owners manual, drake suggested that one could use
either the 3-400Z or the 3-500Z tubes with same results as far as the output
power goes. There is an advantage to used the 3-400Z series tubes as the idling
current (when amp is key without excitation) will be considerably lower with
the 3-400Z tubes. Another advantage is that the gain (amplification factor) is
higher with the 3-400Z so less drive to achieve the same output. The only
disadvantage is that the plate dissipation with the 3-400Z is 100 watts per
tube compared to using the slightly larger 3-500Z tube. So unless you're going
to run rtty or am with the amp, don't be afraid to keep the 3-400Z tubes in
your SB-220.
73 from Fern
----- Original Message -----
From: "WLI" <lgp@wlionline.com>
To: <amps@contesting.com>
Sent: Sunday, April 26, 2009 2:39 PM
Subject: [Amps] SB 220 with 3 400 tubes
>I am looking a purchasing an SB220. I have two to choose from. One has a
> pair of 3 400 tubes and the other has 3-500's. The one with 3 400's looks
> cleaner but I am not sure if the tubes are equal. Can some one tell me if
> the amp with the 3 400's is as good or if there are any problems with this
> substitution.
>
> Thanks
>
> _______________________________________________
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> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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