[Amps] Switching Supplies for High Current Filaments

[Fuqua, Bill L]

My problem with using switching supplies this way is that they are operating in a strong RF field.
If the RF causes the switching supply to stop regulating as it should and suddenly increases the output voltage
it could be very bad.
73
Bill wa4lav

________________________________________
From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of Jim Thomson [jim.thom at telus.net]
Sent: Wednesday, October 06, 2010 12:00 AM
To: amps at contesting.com
Subject: [Amps] Switching Supplies for High Current Filaments

Date: Tue, 5 Oct 2010 07:34:41 -0700
From: Patrick Barthelow <apolloeme at 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 at 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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