[Amps] 3-400Z vs. 4-400A

[Richard]

>> Because other options are open season... One 
>> might judge the value of a Dahl retrofit xfmr. Some 
>> vintage Henry amps (with excessive filament and 
>> Anode values) arrived with 3-400z's on board, an 
>> SB-220 might be considered a candidate should 
>> the owner have a supply of cheaper 4-400's when 
>> the original tubes go away.  The original post 
>> asked for information to compare the two tube 
>> types... the posted reply was very useful, on topic 
>> information. 
>
>Better get a new plate tuning capacitor and a new bandswitch while 
>you are getting the new transformer...because the old components 
>won't take an increase in voltage.

As I recall, the Tune-Caps appear to be identical between the 2k-4 and 
the 3k-A, which uses a higher DC supply voltage. 
>
>Watch the little fixed caps and electrolytics caps also.
>. 
>> I've found the 4-400 a bit "stiff to drive" compared 
>> to the 3-500z, but it's a nice tube to play with.  One 
>> could easily apply a bit of screen voltage for lower 
>> drive (and higher gain) applications. The control 
>
>In grounded grid there is hardly any significant change when you 
>apply bias, ...

There can be no screen-grid amplification unless the AC driving potential 
exists between the screen and the control grid.  In G-G operation, the 
screen and the control grid are at the same AC potential because they are 
both AC grounded.

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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