"Iain Churches" <IainNG@[EMAIL PROTECTED]
> wrote in message
news:824Pj.340419$G71.82199@[EMAIL PROTECTED]
> ... 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) ...
See: "slow turn on regulator", page 15.
http://www.national.com/ds/LM/LM117.pdf#page=1
For better availability use the LM317 equivalent.
Using that circuit, in fact you apply a slow rise heater voltage
i.s.o. a current limited voltage.
The time it takes for the (heater) voltage to rise to final value
is determined by the R3.C1 product. I'd say use the values shown
for a start but increase/decrease C1 to your liking.
Make R2= 970ohm for an output of 6.3V (2K18 for 12.6V), or follow
the formula on page 1 for more convenient combinations of R1 & R2.
The input voltage must be at least 2.3V more than output (@[EMAIL PROTECTED]
1.5A).
With input voltage too low mains ripple will appear on the output.
With input voltage (too) high the regulators will get (too) hot.
> ...and one at 3A (a pair of EL34's)
For 3A of total current f.e. a LM150/250/350 could be used,
however LM317's are usually abundant as "surplus" items so
it's cheaper to use 1 LM317 per tube than 1 LM350 per pair.
Also, but subjective, chassis mounting of TO220 packaged
LM317's I find more convenient than TO3 packaged LM350's.
Even if more (and more) regulators are added to cope with heater
current demand, all components shown in the page 15 application,
except the regulator itself, are required only ONCE. For a graphic
representation see page 19 "Adjusting Multiple On-Card Regulators
with Single Control".
You would need 1 reg for two B9A's and 1 reg per EL34 in your
application, totalling 3 reg's but just 1x R1/R2/R3/C1/T1/D1.
Note that R1 in the "multiple reg. configuration" is of a lower
value than in the single reg. config, accordingly R2 must be of
lower value (485ohm) to satisfy the formula for Vout = 6.3V.
Regards,
Jan
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