Hello Nermin,
I tried this with a 4-400 and it wasn't working.
The low R of the high current, directly heated, cold
cathode caused the PC switcher to lock into protection
state. Usually, these protection circuits locks the PS
at (even for very short time) overloads, both for
output +5V and for overvoltages.
You may modify them for slow rising (ramp) of
the output voltage. I used a potentiometer in the
feedback circuit for adjusting the output voltages
when "formatting/degasing" some tubes.
Anyway, open the PS and look at the components.
For "real" 20 amps continuous output, the 5V shottky
rectifier have to be at 30 amps rated, output transformer
EE33 core size, the output filtering capacitors to be
125 C deg type, the input filtering 330 to 470 uF and
to have inrush current limitter (usually low R thermistor).
It is also better if the switching power transistor to be
not the usually TO220 case types, but larger ones.
Many of these PS are overrated.
I saw some of them rated at 25A/5V and 7A/12V
having 20A in a TO220 case rectifier for the 5V,
two 3A for the 12V output and EI28 core transformer.
It were labeled "200W" and rated 5V/20A, 12V/7A,
but the manufacturer warned us about the 100W total
"real" output.
Usually the PC switching PS are using the TL494 IC
or equivalent at about 30 kHz switching freq.
The ATX style have also a simple +5V at 0.5A
switcher used for stand-by and for remote control.
If you need I can send you a sample diagram.
I'm servicing these for five years now...
Maybe I'll use one (or two?) of these for a Harris
RF110A amp (two 4CX1500B at 6V/10A each
+ two 8122 at 13.5V/1.3A each), if I'll not find
a properly transformer...
73s and Good Luck,
Traian
Nermin Bajramoviæ wrote:
> Hello list,
>
> having a number of PC power switching supplies laying around, usually 20
> amps at 5v and 7-9 amps at 12 volts I wonder whether anyone of you, have
> tried to use them for projects in amplifiers. Guess 5v could be used for
> heating 8877, 3-500Z etc.. 12V for other lamps as well. Any ideas or clues,
> surge capabilities. Oh, yes I have seen the Amp project of K5AM in QEX but
> he did not use the power switchers.
>
> Thanks Nermin S58DX
>
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