[Amps] SMPS use in tube based amps

[Radio WC6W]

--------------------------------------------
On Thu, 9/19/13, Ben Burkhart <bsburkhart at gmail.com> wrote:

 Subject: [Amps] SMPS use in tube based amps
 To: amps at contesting.com
 Date: Thursday, September 19, 2013, 1:22 AM
 
> Hi:

Hi Ben,

>     I am looking to make / cook-up a home brew amplifier as both a rite of
>passage and to challenge myself. My main use is portable as I have no QTH
>at this time. I have a Flex 1500 and enjoy using it, but would like a bit
>more than QRP at times. With tube prices really high 3CX800 (Hi-HI) are at
>this time I would like to use possibly a GI-46B or GI-7BT in a grounded
>grid configuration.


   Correct me if I'm in error but, isn't the Flex 1500 a 5 watt rig?  Grounded grid isn't going to get you where you want to go.


>   Hence the need for a lightweight power supply for 2.2kv
>@ 400ma. Some or most of the transformers I have found are in the 40LBS+
>range and are a little heavy for portable use.

    Perhaps, you're looking at old iron.  A modern transformer at that power level should come in around 20 lbs.

    If you're concerned about tube costs, why not go with something like a pair of 4CX350's?  They don't seem to be in vogue and therefore sell for reasonable prices on Epay.  Even more reasonable if you go with the 26V heater version (F suffix) as those won't just drop into a 4CX250B socket.

    Or... perhaps a single 4CX600J.   When I last looked, a guy with a dozen or so was trying to sell some with no takers.

    Five watts of drive will be sufficient for these parts.

>    I am a networking engineer by trade with a bit more than basic under
>standing of electronics. I have been looking at several amplifier designs
>by several different people / companies and came across an observation thus
>my question. Why are all B+ power supplies simple linear setups?

  Precisely because they are simple and cost effective.

  Why not use a switch mode power supply?

  They cost more and are less reliable.

> I have yet to see one in a tube based
>amplifier. SMPS would allow for better power factor, smaller size and w
>eight, better B+ regulation, smaller filtering capacitors.

  All true except for the filter caps.  The energy storage requirement is moved to the primary side but, remains the same and requires capacitors with higher capacity at lower voltage yet of similar volume.

>   I wouldn't really accept the idea that SMPS designs are more complicated
>as they are well understood and documented.

   Understanding & documentation doesn't overrule complication and parts count.

> I have the idea that the
>fundamental switching or voltage feedback freq would wind up in the output
>but with a properly low pass filter that should not be an issue.

   The required filtering is easily implemented.

> So the question is: Does the amateur community use linear supply as it has always
>been this way or am I missing something.

  The conventional supply is cheaper, and inherently more reliable due to lower component count.  Way more reliable if oil or plastic filter caps are used instead of electrolytics.

   Few amateurs care about power factor or regulation, leaving size and weight as the only advantages of a switcher.

   If you still care to pursue it, a (one) KW supply should not be all that hard to realize.  I have a good list of references I can forward if you are interested.

   The transformer is still a key part though at your power requirements you might keep an eye out for one of the Panasonic Microwave Ovens with a switching supply "on the curb".  That supply is not usable as-is since it is designed for a fixed load current and has poor filtering but, the transformer itself would be useful.

73 & Good morning,
   Marv WC6W 

http://qsl.net/wc6w/  
 
> Ben Burkhart
> KJ4CGX
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