In article <824Pj.340419$G71.82199@[EMAIL PROTECTED]
>,
"Iain Churches" <IainNG@[EMAIL PROTECTED]
> wrote:
> Can I suggest a topic for you? A current limiter for tube heaters.
> People are keen to use voltage regulation, which doesn't seem to
> me to be so im****tant. Heaters are specified at +/- 5% so
> anything between 6V and 6V6 for a 6V3 heater is within tolerance,
> and with a wirewound pot between two 'lytics one can get it spot on.
> But heaters draw huge currents at switch on. Do you have a circuit,
> using those funny black things with ****ny legs, that could current
> limit? Two circuits would be of interest. One at say 1.2A
> (a pair of B9A's) and one at 3A (a pair of EL34's)
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.
Regards,
John Byrns
--
Surf my web pages at, http://fmamradios.com/
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