> 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.
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, except it evens out grid current more.
> The 4-400 is a tetrode and some very
> innovative things can be done with that
> old swan amp. Just ask.... right here!
The best way to use the 4-400 is to plug it in and play, and live
with the slight gain reduction. Otherwise, you might as well build a
whole new amp. To make a Swan work like it should with a tetrode,
you'd either do that or have external parts in other cabinets just to
support the amplifier.
Of course I guess you could saw it in half and stretch the chassis so
all the extra parts would fit, but I seriously think using it as-is
would be best unless you want to build a new amp around the sockets
and a few other parts.
73, Tom W8JI
W8JI@contesting.com
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