11-08-2016, 08:13 AM
If a valve filament goes o/c then no current will flow through the heater dropper resistor. (R20 1690R) Hence it won't drop any volts and the top of the heater chain will be at HT voltage. Actually higher than HT, since there's no heater current being drawn through the other dropper resistors. The cap in the heater chain won't like this
Not enough current availble to make the cap go bang but probably enough to wreck it.
A zener across the heater chain might be a good idea but remember that they aren't very precise things. The knee is somewhat soggy so some tests might be needed to establish that it will not draw current in normal use but will limit to a sensible voltage if a heater goes o/c.
Not enough current availble to make the cap go bang but probably enough to wreck it.A zener across the heater chain might be a good idea but remember that they aren't very precise things. The knee is somewhat soggy so some tests might be needed to establish that it will not draw current in normal use but will limit to a sensible voltage if a heater goes o/c.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
