In article
<ccaa80f9-a3b9-4ce4-9b91-6658b7a70c77@[EMAIL PROTECTED]
>,
Peter Wieck <pfjw@[EMAIL PROTECTED]
> wrote:
> On Apr 22, 9:41 am, John Byrns <byr...@[EMAIL PROTECTED]
> wrote:
>
> > Your comment "one at 3A (a pair of EL34's)" suggests that you are
> > contemplating running the EL34 heaters in parallel, this seems like a
> > singularly bad idea to me. Unless the heaters in both tubes are
> > identical the current will divide unequally between the two heaters.
> > There is also no guarantee that you will get 6.3 volts across the
> > heaters, so the heaters will likely not be operating at either rated
> > voltage or current. If I were using current regulation I would
connect
> > the two heaters in series so that I would be guaranteed that the
heaters
> > would operate at their rated current.
>
> Are you sure?
Yes
> Parallel devices see the same voltage along the entire circuit, don't
> they?
Yes
> Like ties on a railroad track?
I'm not sure what you mean with the railroad tracks?
> I am thinking of the dozens of
> lamps in our house, each one "dividing" current unequally between the
> heaters (filaments)... and they are not hardly identical.
Correct, but the parallel connected lamps in your house are feed from
what is essentially a constant voltage source, not a constant current
source. If you house hold power was supplied by a constant current
source, each time you turned on another lamp the ones that were already
on would get dimmer, and if you had only one lamp on it probably
wouldn't last very long before burning out.
When I was a kid I was always fascinated by the series connection used
by the city for some of the street lights. I don't know what the
voltage rating of the bulbs was, but they were incandescent types and a
number of them were wired in series across the 2,400 volt distribution
feeders.
> Now, series devices may see problems depending on the nature of the
> two (or more) devices in the string?
Sounds likely, but parallel connected devices are no different and may
also see problems depending on the nature of the two (or more) devices
connected in parallel.
Regards,
John Byrns
--
Surf my web pages at, http://fmamradios.com/
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