>> 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.
end
|