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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