On Mon, 24 May 2004 21:18:11 GMT, "Fabio Berutti"
wrote:
AFAIK all valve producers gave at least a 5% allowance for heater
voltage/current. If Your mains supply is reasonably stable I'd say that a
simple CRC or CLC rectifier is OK; being the tubes used in fixed (grid) bias
(I suppose, being a 100+W tube, it is used for POWER) it is feasible to feed
2 of them from the same tranny & rectifier and reduce a bit the pounds of
steel to be used (I already had my spine repaired by a surgeon and it was no
fun at all, I now set the threshold for my projects to = 50 pounds). The
voltage can be adjusted by trial and errors simply varying a bit the R in
the CRC filter. I did it for a phono preamp (OK, 1.5 amp all together..)
and it works. Plain and easy.
IMHO I'd use plain AC filaments in such a beast. I read a WE (or maybe it
was from RCA) paper stating that large power tubes were better used with AC
filaments, because in this way filament temperature tends to average (being
either positive or negative 50 times per second), while with DC filaments,
in fact, a part of the "cathode" always works with a hotter bias and the
other with a lower one, - the filament temperature (and electron emission)
is not symmetric - the valve does not work properly. This paper showed a
graph of the filament temperature against it length in a DHT, and well, a
difference of only a few volts in a tube having a bias of about 100V was
enough to have either one half too cold or one half too hot. I'm sorry I
don't remember where I found it.
Ciao
Fabio
Fabio
thats a good point, ie. with the cathode/filament temperature, in
Pete Millets site, he mentions that he reverses the dc heater supply
every time the unit is switched on. this is to even out wear on the
filamentary cathode, don't know if this has any merit or not, it is
something to do with one side of the cathode being more negative than
the other so more electrons are emitted. sounds plausible, but I
don't know if the distribution of electron emission is too much to be
worried about, anyway see my later post, I am going back to AC with
hum pots.
[the 813 uses a filamentary cathode, ie. direct heated].
kind regards
bill.
"bill ramsay" ha scritto nel messaggio
.. .
dear all
I am playing with some 813's at the moment. I am trying to get the
heater supply sorted out.
the 813 needs 10v at 5 amps, the do glow v. bright when lit up.
pretty neat.
I have a breadboard amp going at the moment which someone else has
given me.
The current heater supply uses a 20 odd volt ac transformer, bridge
rectiifer, feeding a 2n3055 based regulator, thing is putting out
about 50watts in heat. as it is stereo there is 100w in heat being
generated.
whenever i model a 5 amp 10V heater supply in PSUD i get some really
whacky readings, ie.
28V transformer to feed 100,000u cap, with a 0.5ohm resistor, then
1000u cap into the tube. ie. 2 ohm load,
or am i missing something here, 28V ac seems a long way away from 10v
dc, or is this an artifact of the high current pulsing away and
charging the caps?
I wanted to build a dc supply that does not generate so much heat in
itself.
any thoughts, ideas etc. especially the printable ones would be
greatly appreciated.
kind regards
bill ramsay.
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