"John Byrns" <byrnsj@[EMAIL PROTECTED]
> wrote in message
news:byrnsj-1CFED7.09332022042008@[EMAIL PROTECTED]
> 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?
It's the tube base designator for a miniature 9 pin, 12AU7 etc etc.
>
>> > 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.
Yes indeed. Usually they are parallel fed and there is no regulator at
all.
>
> 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.
Yes. This thought had ocurred to me. Should there be a regulator
for each tube?
I think this deserves its own thread. Care to start one, with
your thoughts on the matter? John
I am hoping that it might turn into a RAT "project"
and result in a design for a sub-board we can all
use.
Best regards
Iain
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