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Are you sure? yes no

3-400Z vs. 4-400A

Ad
(skipp isaham)1025972899Sat, 06 Jul 2002 16:28:19 +0000 (UTC)
[cut and paste]>> --------- Forwarded message ----------
>> From: 
>> Think about it.
>> The Swan amps don't furnish ANYWHERE NEAR 
>> 3,400 Volts B+.  Why even bother to point out the 
>> bias requirements of a 4-400 operating in GG 
>> with 3,400 volts  on the plate?-
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. 
-
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 
grid could be grounded (bias applied in the fil xfmr 
ct) or dc floated (I don't prefer floating control grids 
if a choice is available). But then you get away from 
the simplicity of zero bias operation. 
Adding tetrode operation to a swan amplifier is 
also not out of the question. There's lots of space
inside....
One or two classic ARRL type 4-400 Handbook 
projects come to mind with lower anode G-G 
AB2 operation. 
->> Unless, of course one wants to point out his 
>> library skills.- 
Pretty rude of you to attack Rich's about his 
post offering valid information. The posted 
information was on topic..  provide your on topic 
information and get off your bitter horse ride. 
->> In case you DO want to up the Swan Amp's 
>> plate voltage to 3,400 volts in order to 
>> obtain the requisite idling current, there are 
>> any number of authorities on the subject, 
>> RIGHT HERE?  Just ask!-
If the answer is on topic, why not post it 
instead of playing personal attack 101 and 
stingy with your info.... buck'o. 
- 
One is not limited to the mentioned 3400 volt 
potentials as a min value to "obtain the requisite 
idling current," there are any number of amps 
members willing to offer up various options 
and opinions without the additional cannon 
fodder (personal attacks) attached. 
- 
The 4-400 is a tetrode and some very 
innovative things can be done with that 
old swan amp.  Just ask.... right here!
- 
cheers
skipp
(Tom Rauch)1026052786Sun, 07 Jul 2002 14:39:46 +0000 (UTC)
> 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 controlIn 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
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