Date: Tue, 5 Oct 2010 07:34:41 -0700
From: Patrick Barthelow <apolloeme@live.com>
Subject: [Amps] Switching Supplies for High Current Filaments
Are there any sensibly priced switching supplies (even surplus) that are small
and light, that could power some of the QRO tubes
with high current filaments? Would, say, a 5v, 30A switcher which could
power a pair of 3-500Zs, be economically
competitive with a 5V 30A transformer, and even if it is not directly, it might
still be worthy of consideration
if it was small enough, and light enough to significantly lower size and weight
in an RF deck?
Would cold start surge current be a problem for switcher implementation for
filaments?
Best Regards,
73, de Pat Barthelow AA6EG apolloeme@live.com
## This was 1st tried on a GS35B 6m amp. The inrush current was so great
that the
switcher thought it was being cro-barred... and went into shut down mode ! A
bigger
switcher was used..and that worked, but the 2nd one was almost double the
capacity
of the 1st one. Also, I believe my buddy had to use a Dc-dc isolation
converter in their some where, to
solve yet another problem.
## In the end, with numerous other problems, like heating of the air variable
load cap, the RF deck was scrapped,
and a new one designed from scratch. 2nd version used 2 x GS35B's... and this
time, 2 x separate conventional
fil xfmr's used, one per tube. The problem with a pair of 3-500Z's is.... the
B- return is via the CT of the conventional
fil xfmr. We gave up on the notion of using switcher's for fil supplies on
oxide tubes. Some have had better success,
so it can be done with oxide tubes. Then you have an adjustable, regulated
supply. They will not work on a directly
heated thoriated tungsten tube. On some of the switcher's... hash and noise
was across some of the HF bands...and
a bitch to filter out completely.
## hammond makes a 5V @ 30A [with CT] conventional fil xfmr...for 2 x
3-500Z's. Runs barely luke warm. It's priced
way below what a dahl is.... and readily available in the usa, through the
usual distributor's. Comes in 2 x version's ,
with or without bell end housings, IE: bell housings or open frame. They
measure 5.5 V no load.. and 5.0 V with a 30A load.
Last I checked a few years ago, it was aprx $45.00 . Their is only one
primary, 115 vac. You can also get it in 5v @ 15A .
They also make a 7.5 vac @ 21 A. A friend in W6 land got his YC-156 fil
xfmr from hammond. The YC-156 fil xfmr was a
torroidal type.
later... Jim VE7RF.
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