"Iain Churches" <IainNG@[EMAIL PROTECTED]
> wrote in message
news:46UPj.341580$1m.74885@[EMAIL PROTECTED]
> One point is still unclear to me. If the current regulator
> is set up for say a pair of 12AU7 in parallel (6V3 heaters
> at 0.3A) and one heater fails, will the current limiter
> "force feed" the other heater with the whole 600mA ?
If one filament fails, the other's still fine, because ...
.... the schematic linked is NOT a current regulator but
a voltage regulator ... with a slow rising voltage when
first switched on. At switch-on the voltage is around
1.8-2.0V, thereafter (slowly) rising to a final 6.3V.
In other words: the filament current at first switch-on
is limited because the voltage at switch-on is limited.
The rate of rise is determined by the R3.C1 product.
Expect a rise-time of a few sec's with values shown.
Increase rise-time by increasing C1 and vice versa.
For the transistor in the application most small signal
PNP's with good Hfe will do, let the junk-box rule!!
For KT88's with an If of 1.6A go for LM350T's (max.3A)
http://www.national.com/ds/LM/LM150.pdf#page=1
For availablility choose LM350(T) i.s.o. LM150(T).
Regards,
Jan
>
> Regards
> Iain
>
>
|
