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Author Topic: Voltage doubler for filament supply?  (Read 24413 times)

Posts: 91

« Reply #30 on: December 08, 2012, 12:07:49 PM »

Looks good. They have a 25 buck minimum, so I would suggest two of the 5 amp and keep one for a spare as
someone else suggested.
Thanks for reply.


Posts: 5688

« Reply #31 on: December 09, 2012, 07:48:39 AM »

Not quite true. Some of the MRI amplifiers I've worked on (including those built in the 1980s through the mid 2000s had switched power supplies for the filaments....

Hi Rick,

Wouldn't you agree, though, that within the scope of this thread, which is involved with the idea of an Amateur Radio Operator attempting to press an unknown design of a switcher from COTS availability for the task meets the criteria of what I posted earlier? 

It should. 

Too many unknowns that may crop up in that situation from my point of view. 

Of course, Ham Radio has always been about experimentation and the breaking of paradigms that result from the hard work of a few individuals sharing their findings, wouldn't want to steer someone with the urge to experiment away from that sort of goal either. 

At the end of the threads, each individual has got to evaluate their own situation and follow suit accordingly, the path that they desire, so there is no harm nor foul in just addressing whatever caveats one might conceive and then let that other person know what they might be in advance, is there? 

Commercial Off The Shelf design would very likely be done by experienced engineers or at least a team led by such, coupled with the time, equipments and what all required to teast and proof the design before production commences.  At least, that's the way these things *should* work <g>...

Also consider that the OP kind of referenced this particular situation as an "economy" move to avoid the cost of a much simpler solution, namely a simple power transformer....


Posts: 14491

« Reply #32 on: December 09, 2012, 10:47:51 AM »

Trying to use a switching supply is full of potential problems, most of which have been identified in other posts. KISS (keep it simple stupid) is usually the best solution (i.e. a 12VCT transformer).

Of course, if your goal is only to restore the amp then just using the originally specified tubes is the most reasonable solution.

Bob  AA4PB
Garrisonville, VA

Posts: 815

« Reply #33 on: December 14, 2012, 09:58:09 PM »

To provide an example of working out a problem.
I bought several 117 volt ac coax relays brand new military just because they were cheap and no one wanted them.
How was I going to use them on a tower?
No way was I wiling to send 120 vac to the tower.
What to do? Came up with the idea of building a power supply using 28 vac transformer secondaries at 4 amp rating.
Send this out on a line to the tower to another transformer  of the same design to step up to 120 at the relays.
In between the 28 volts was resistor adjusted to make the relay voltage 117 on the tower mounted unit to work at spec.
Most have no idea how much more is involved when AC is thrown around like this.
The transformers need to be class B rated, account for efficiency losses etc.
The whole design had to be mocked up including the line losses so temperatures could be measured, voltage checked, ac curnt measured for fuse sizing on the 28 volt line  and a time test to see if anything is being missed or overheated.
So far in 2 years the design has never failed.
It may have been easier to rewind the relay cores but I did the challenge to see if I could get away with it.
The reason why was a tower with 3 vhf/uhf beams on  one low loss 7/8 Heliax coax cable for low loss weak signal SSB use.
No body but a nut like me would even try such a stunt.
 Again for OP amplifier use a transformer with the proper rating and be done with it.
Any other way results in failure and way to much expense before giving up and dong it right..
Good luck.

Posts: 618

« Reply #34 on: December 15, 2012, 07:07:45 AM »

No way was I wiling to send 120 vac to the tower.

I'm confused.  Why not?  Done on commercial towers all the time (think obstruction lighting).  Unless I misread, your tower is for VHF and up so don't think interference should be a problem.
A dedicated line and a Ground Fault breaker should cover the safety concerns.
What am I missing?

Posts: 349

« Reply #35 on: January 04, 2013, 05:44:56 PM »

Jan you said you need 8 Amps. If true, a 4 Amp switch mode nor any other arrangement would work. As was mentioned earlier, if you have a series circuit, the current will be the same at all points in the circuit. The least rated transformer ie 4 amp would be your limiting factor.

Posts: 815

« Reply #36 on: January 04, 2013, 09:57:41 PM »

Tom , accept it!
I'm not sending 120 vac to my tower for any reason.
I don't care what the commercial systems do.
You keep trying to intimidate people just to be ahead all the time. You are confused!
It doesn't work with me.
Good luck.

Posts: 31

« Reply #37 on: January 07, 2013, 08:33:10 PM »

I need to get 6.3V @8A (SB-200 transformer) to 12.6 @ 3.6A (Russian GU-74B). Is it feasible to build a voltage doubler, much like the HV doubler to get the higher voltage? If not, how could I do it without adding a second transformer.
Hey OM:
I'd use a half wave supply off the Mains, a Buck SMPS takes 115Vac half wave so the ground would be common, with about a 5% duty cycle use a LM2576adj driving an IGBT and a voltage divider for feed back and the filament choke for the buck coil.

73 OT
de n8zu
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