In article <etmPj.340844$A97.323045@[EMAIL PROTECTED]
>,
"Iain Churches" <IainNG@[EMAIL PROTECTED]
> wrote:
> "John Byrns" <byrnsj@[EMAIL PROTECTED]
> wrote in message
> news:byrnsj-D6B303.08411522042008@[EMAIL PROTECTED]
> > In article <824Pj.340419$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)
I forgot to ask, what is a "B9A", I can't find a listing for this tube
type?
> > 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.
>
> Please explain, John. Everywhere I measure the heater
> voltage in my amp I get 6V3 spot on, with no variation
> anywhere. I have always connected heaters in parallel
> without any kind of current regulation. All European
> makers seem to have done this. So far I have found
> no ill effects.
Most commercially built European amplifiers with parallel connected
heaters that I have encountered feed the parallel heater circuit from
something approximating a voltage source, not a current source such as
you are proposing.
Another thought, what happens if you accidentally power up your
amplifier with one of the EL34s not plugged into its socket? Seems like
the remaining tube is going to see 3A through a heater rated for only
1.5A.
Regards,
John Byrns
Regards,
John Byrns
--
Surf my web pages at, http://fmamradios.com/
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