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Re: [Amps] Switching Supplies for High Current Filaments

To: "Jim W7RY" <w7ry@inbox.com>
Subject: Re: [Amps] Switching Supplies for High Current Filaments
From: "Hsu" <hsu4qro@gmail.com>
Date: Thu, 7 Oct 2010 11:35:02 +0800
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I have a 5A 200A  swps for filament, it pull from a TV transmitter ( made in 
Italy)
the ps made in USA.In 1990s, there are some filament  swps manufacturers in 
China.
They all promises that if you replace the AC transformer filament power supply 
with swps,
your tube life will extend 1.5  times or longer.
 Some design tips:1) The switching power supply's  main power transformer must 
have very good  insulation( over 10kV)
between  primary and secondary.2)the PS must with soft start.3)give more  
attention at noise problem.
      73!Hsu 
----- Original Message ----- 
From: "Jim W7RY" <w7ry@inbox.com>
To: <TexasRF@aol.com>; <jim.thom@telus.net>; <amps@contesting.com>
Sent: Thursday, October 07, 2010 11:01 AM
Subject: Re: [Amps] Switching Supplies for High Current Filaments


> Agreed! Ever try to hook a headlamp across an Astron power supply?  Pretty 
> tough to do..
> 
> 
> 73
> Jim W7RY
> 
> 
> 
> --------------------------------------------------
> From: <TexasRF@aol.com>
> Sent: Wednesday, October 06, 2010 7:40 PM
> To: <jim.thom@telus.net>; <amps@contesting.com>
> Subject: Re: [Amps] Switching Supplies for High Current Filaments
> 
>> The problem with switchers or using any regulated supply is the cold
>> resistance of the heater/filament is typically 10% of the hot resistance. 
>> That
>> issue is automatically handled by the current limitations of a typical
>> filament  transformer. The transformer becomes pretty much a constant 
>> current
>> source until  the heater temperature rises enough to get the transformer 
>> out of
>> saturation.
>>
>> On big tubes requiring many amps of filament current this can be a real
>> problem. If the transformer has to supply say 30 amps, then it will supply
>> many  times more current than that for short periods of time. A cold tube 
>> can
>> be  subjected to very high stress under these circumstances and can even 
>> have
>> the  filament burned open, just like a 100w light bulb blows out. No
>> problem with the  $1 light bulb but loosing a big tube that way is heart 
>> breaking.
>> (Been there,  done that, have multiple tee shirts).
>>
>> The solution to the over current problem is reducing the startup voltage
>> enough that the 10% filament resistance still draws rated current. That 
>> takes
>> 10% voltage according to ohm's law.
>>
>> So, for any regulated and current limited power supply, there needs to be 
>> a
>> method of starting at low voltage and ramp it up as the tube warms up.
>>
>> Being the concept guy, I will bow out at this point and leave the answer 
>> to
>> others. I have the answer for transformer filament power sources but no
>> clue how  to do it with a switcher or any other regulated/current limited
>> supply. If it  was actually a current limited supply, not a current 
>> shutdown
>> design, all would  be well and the tube could warm up with a constant 
>> rated
>> current source. A  regulated current design instead of voltage would be
>> wonderful.
>>
>> By the way, that 10% resistance figure applies to light bulbs as well. The
>> hot resistance can be estimated by r  equals voltage squared divided by
>> wattage rating. That is the well known power = e squared divided by
>> resistance formula turned around backwards. The cold resistance can be 
>> measured  with
>> a VOM or DVM.
>>
>> 73,
>> Gerald K5GW
>>
>>
>>
>> In a message dated 10/5/2010 11:01:14 P.M. Central Daylight Time,
>> jim.thom@telus.net writes:
>>
>> 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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