On Sep 16, 2004, at 5:22 AM, lncarman wrote:
I've heard over the years of some amp builders floating the filament
transformer. I was
told that you isolate the filament transformer from ground and add two
chokes
in the primary side with bypassing. Since the primary side is 115V or
220V the
amperes demand would be much less on the primary side. Looks like any
RF would
be suppressed greatly by the filament transformer and you wouldn't
need a lot of
uH in the primary chokes to finish the job. Has anyone tried this???
--- It is common in commercial g-g applications, Larry. All filament
xfmr windings are RF-bypassed to the core and the transformer is
floated on a insulating sheet of ABS or G-10. A bifilar choke is
placed in the primary of the transformer. After installation, the C
from the core to gnd is measured and this amount is subtracted from the
calculation(s) for C2 in the tuned-input(s). An additional choke is
connected to the fil. secondary CT to provide the DC path for electrons
going to the the cathode from the –HV. As I see it, filament currents
of more than 30A are a candidate for this solution. Thus, a filament
choke for a 3cx10,000A7/8160 (7.5v/99A) would typically be Much
smaller than a filament choke for a pair of 3-500Zs (5v/30A). In this
case, with 240v mains, the filament choke for the 8160 would only need
to be wound with #22-ga, wire, while the choke for the 3-500Zs would
need to be wound with #8 gauge wire.
- cheerz
Regards,
Larry N5BIP
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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