On Oct 27, 2004, at 7:24 AM, Tony King wrote:
At 10:13 AM 10/27/2004, k7fm wrote:
Will said:
"You have to keep in mind the current surge there until the heater
warms up.
The colder the heater is, the more current it draws. I would use a
conductor
with at least 750 cir mils per ampere. For 3 amperes, that equals out
to be
about 16 AWG wire for the minimum"
The filament choke should not take into account any surge current,
and there
is an advantage in limiting the wire size to limit surge current. By
limiting the wire size, the smaller wire will limit the surge current
and
protect the tube. Since the choke is presumably in the slipstream of
air, a
significantly smaller size of wire can be used. If there is no other
means
to protect the filament surge current, then this is an opportunity to
protect the tube and wind a smaller choke.
Since chokes always seem to be just large enough to not fit where you
want
them to, take advantage of downsizing.
Very interesting guys! I was thinking that with a step start on the
filament, the surge would be of little consequence anyhow. Keeping the
choke smaller would certainly make it easier for constructing the
input and even more desirable for those folks that are thinking of a
retrofit to desk top amps.
Based on Rich's earlier comments I would think you could easily go
smaller than #16 wire on the choke and reduce the physical size or at
least get enough inductance for 160 in the same package. What do you
think the target inductance should be for effective use on 160?
Tony -- The stock, 9uH, filament choke in a SB-220 works okay at
1.8MHz provided that one adds -j100-ohms of XC (900pF) to C2 of the
160m tuned input to cancel the +j100-ohms of XL from the 9uH.
73, Tony W4ZT
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|