25 Apr
2005
25 Apr
'05
10:39 a.m.
Subject: Re: small valves
From: "Dwight K. Elvey" <dwight.elvey at amd.com>
Date: Mon, 25 Apr 2005 09:57:08 -0700 (PDT)
To: cctalk at classiccmp.org
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.
Dwight
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.
Allison