[Amps] SB 220 with 3 400 tubes

[Fern]

        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 at wlionline.com>
To: <amps at 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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