Nope! A linear type. And yes, the power supply was on. It was a 20 or 35 amp
supply.
73
Jim W7RY
--------------------------------------------------
From: "Jim Thomson" <jim.thom@telus.net>
Sent: Wednesday, October 06, 2010 9:26 PM
To: "Jim W7RY" <w7ry@inbox.com>; <TexasRF@aol.com>; <amps@contesting.com>
Subject: Re: [Amps] Switching Supplies for High Current Filaments
> ## The typ cold resistance of a light bulb is 10% of the hot resistance.
> On tubes, it's
> even worse, typ 12%. On the few switcher's we experimented with.. all
> had
> a built in ramp up
> feature on start up. IE: with no load on the switcher's output, the
> output Vdc would ramp up
> anyway. With a load ALREADY connected [oxide tube only]... the switcher
> is
> then turned on... and it goes
> through it's ramp up feature. Between that and the current limiting
> feature... the switcher will
> not cro-bar itself. But this only worked if the switcher's output
> current
> rating was aprx double the
> tubes rating. IE: tube fil was 3.6A.... a 8A switcher will just
> work...a
> 5 A switcher would not work.
> --------------------------------------------------
>
>> Agreed! Ever try to hook a headlamp across an Astron power supply?
>> Pretty
>> tough to do..
>
> ## was the astron turned on 1st..... then the headlamp connected ? Or
> did you
> hook the headlamp to the astron 1st.... then turn on the astron ? Is the
> astron a
> switcher type ?
>
>> 73
>> Jim W7RY
>>
>> > --------------------------------------------------
>> From: <TexasRF@aol.com>
>>>
>>>>> 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.
>>>
> 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.
>
> ## On my little lab type switcher supply, the current limit can be
> adjusted to any value.
> If set for normal rated tube current [ + maybe 1%] it will perform just
> like you wanted.
> You can cro-bar the output all you want, and all it does it put out the
> max
> current you dialed
> in. So this type of switcher will work as well.
>
> ## None of these switcher's will work on a thoriated tungsten tube like
> a
> 3-500. The B-
> return for any thoriated tungsten tube is via the CT of the conventionl
> fil
> xfmr sec.
>
> Jim VE7RF
>
>
>
>
>>>
>>> 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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>>>
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