--------------------------------------------------
From: "Jim Thomson" <jim.thom@telus.net>
Sent: Thursday, October 07, 2010 5:39 AM
To: "W2XJ" <W2XJ@W2XJ.NET>
Subject: Re: [Amps] Switching Supplies for High Current Filaments
> ## I was going to say on a reg ac fil xfmr, the B- return is through the
> CT of the
> sec of the fil xfmr. Then you won't get 60 hz hum modulation. The
> switcher,
> being dc output, you could probably return the B- to one side of the
> cathode/fil,
> via a single solenoid choke. You would still require the normal bifilar
> fil choke,
> one choke per leg..for the +/- dc output of the switcher. Cold ends of
> the bifilar
> would have to have bypass caps....to chassis. I stand corrected, the
> switcher probably
> can be used on a directly heated GG triode. As long as the switcher is
> not pumping out
> loads of harmonics and junk, it may well work. Ok, now all I require is
> a switcher that
> will put out 7.5 vdc @ 50A CCS.... and a 2nd one that will put out 7.0 vdc
> @ 80A.
>
> ## at present, I use conventional AC xfmr's, with a CT on the sec. I
> manually soft start
> the tube with a small 0-240vac @ 5A variac. A surplus 750va sola
> constant V xfmr feeds
> 240 vac to the input of the variac. There is a cam lever on the shaft of
> the variac that
> activates a microswitch......when variac is almost fully CCW.
> Microswitch activates
> the coil of a dpdt relay, whose contacts apply 240vac from the output of
> the sola,
> to the input of the variac. This rigmarole is done, so IF I forget to
> turn down the variac
> when finished for the night, and just shut off the 240 vac input to the
> sola.... nothing bad
> will happen the next night..with variac cranked way up in it's normal
> mode. IE: come in the
> next night, turn on sola, and zero volts on the input of the variac...
> UNTIL the variac
> is 1st turned down to almost fully CCW, so the microswitch will
> activate. Done this way,
> their is zero chance of defeating the manual step start.
>
> ## The sola was required because my line V was varying all over the map
> for almost 2 yrs. The
> sola will regulate to within a fraction of 1% , when line V varied from
> 233-247 vac. The sola
> weighs 66 lbs..and is a real pig, and runs hot. The 240 vac @ 5A variac
> is no small item either,
> and a 7.5v @ 50A fil xfmr is not exactly light iron, nor is the 80A fil
> xfmr. I use a 5:1 current xfmr
> set up, with the torroid looped through one leg of the fil xfmr sec, to
> measure fil current. Panel
> meter is a 0-50A unit. 5A flows through the torroid of the current
> xfmr...which drives the meter.
> Meter is calibrated to read 0-50A... but has only 5A flowing through it,
> when 50A flowing. I use
> a pair of 200 uh chokes, one per leg, right at the socket,,, then wired
> with 18 ga wire up to the
> RF deck 0-10vac fil V meter. A 500-1000 ohm , 2w mof in each leg at the
> panel meter end, plus
> .01uf bypass caps. That mess is also in parallel with a pair of banana
> jacks...so I can plug in my fluke 87.
> RF does not get into the fluke with drive applied to the directly heated
> cathode. If the banana jacks
> are accidently shorted, the resistor's in each leg limit the current. The
> same fil V and I measuring
> setup is also used on a YU-148. Again, no RF gets into the fluke dvm
> with +60dbm of drive.
>
> ## a switcher could eliminate all of the above, including the metering.
> I wonder if any broadcast Tx's
> have gone the switcher route, for directly heated GG triodes, or grid
> driven tetrodes ?
>
> Jim VE7RF
>
> --------------------------------------------------
> From: "W2XJ" <W2XJ@W2XJ.NET>
> Sent: Thursday, October 07, 2010 3:58 AM
> To: "Jim Thomson" <jim.thom@telus.net>; <TexasRF@aol.com>;
> <amps@contesting.com>
> Subject: Re: [Amps] Switching Supplies for High Current Filaments
>
>> If the supply is not ground referenced there is no good reason it can not
>> be
>> used in any topology.
>
>
>> Jim, please bring me up to speed on why the switcher will not work with a
>> directly heated tube. I am not challenging the information; just asking
>> for enlightenment!
>
> 73,
> Gerald K5GW
>
>
>>
>> On 10/7/10 6:00 AM, "Jim Thomson" <jim.thom@telus.net> wrote:
>>
>>>
>>>
>>> --------------------------------------------------
>>>
>>>
>>> ## The caveat is you can't use any version of a switcher... when used
>>> with
>>> a
>>> directly heated [thoriated tungsten] GG triode. However, ur scheme
>>> would
>>> work
>>> with directly heated tetrodes.... like a 4CX-5000.
>>>
>>> Jim VE7RF
>>>
>>>
>>
>>
>>
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