small valves

Allison ajp166 at
Mon Apr 25 12:39:59 CDT 2005

>Subject: Re: small valves
>   From: "Dwight K. Elvey" <dwight.elvey at>
>   Date: Mon, 25 Apr 2005 09:57:08 -0700 (PDT)
>     To: cctalk at
>Hi Stan
> I've done similar. I've taken one of those small 100W
>inverters and rewound the transformer on it to provide
>all the voltages for my older battery powered Atwater
>set. It just runs from a 12 volt gel cell. I tapped
>of the primary to provide the filament voltage and
>used the secondary with tape to provide the rest.
>As I recall, there was one -C and two +B voltages.
>I used no regulation, just used the right rinding
>ratios. One has to remember, these old radios
>were made to run form carbon-zinc cell in most cases.
>I did put a pot on my C cell. The original was -4.5v
>but I found that it works better, with less distortion,
>when set at about -3.5v.

Good approach.  I enjoy building and winding my own cores
be they EI iron or powered iron/ferrite types is part of 
that.  Switching mode PS design is an art in itself. Part
of the fun is building for good efficientcy and for powering
tube designs that means knowing the load.

An aside is don't run regens off inverter or switching supplies
as the gain is high enough to negate reasonable shielding 
and bypassing.  For that I find common alkaline 9V batteries 
in series do well for the typical 27-90v range and exhibit 
good life.


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