Hal wrote:
Some time ago, mention was made about using an MOV near the power
amplifier tube as protection against transient surges, perhaps in the
filament area.
Looking at Mouser's MOV selection, the reader is presented with a
plethora of selections, each one having a 1MHz. capacitance listing.
My question now for the reflector is would the inherent capacitance in
an MOV mounted near the final and connected to the wiring going into
the tube have an effect on the circuit because of the device's inherent
capacitance, or should a Metal Oxide Varistor not be used at all, with
a better choice being perhaps a gas-filled device?
At voltages below breakdown, MOVs look like capacitors of a few thousand
pF so they can be used wherever a real capacitor would be OK. In
practical terms, you can connect an MOV across almost any existing
bypass capacitor.
A good example is an MOV connected across the screen bypass capacitor of
a tetrode, to protect that capacitor from voltage breakdown (which would
probably cost you a whole new socket).
Spark gaps are only a few pF, so they can be connected directly into
most RF circuits, for example across the transmission line.
Different devices, different uses. MOVs start to protect at only a
little more than their maximum rated operating voltage. Spark gaps may
protect better, but only when they've fired - and that requires a much
larger impulse voltage than the rated operating voltage.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|