If it's across the filament, it's just for filtering. Capacitors will always work better
if located at the points that they filter than at someplace remote.
if located at the points that they filter than at someplace remote.
Ok, that's basically what I figured. What's the target when filtering something like the heater filament? I understand frequency targets when filtering an audio signal, but not something like power or heaters.
It could also be part of the heater elevation circuit, although the value seems high for that.
jeff
jeff
Heaters are low impedance and high current, so a capacitor has to be large to do much, 1000uF and up.
With a full wave rectifier followed by a CRC filter, the first C holds up the peak rectified voltage and limits the sag.
The next RC filter then reduces the remaining 120Hz ripple to an acceptable level. There's some DC voltage drop
across the R, so that is traded off against the value of the second C, and the power dissipation in the R.
Or use a regulator instead.
The time constant of the RC ripple filter would be the second C times the parallel combination of the R
and the resistance of the filaments. Then to get some degree of ripple filtering, set the LP filter corner
at a factor of two to ten times lower than 120Hz.
Here's the heater power supply schematic, as well as the B+ power supply schematic. Both are provided on the same board as the line stage.
(Moderation edit: Remove images per request)
(Moderation edit: Remove images per request)
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As requested.