Gareth Magennis wrote:
Hi,
what is the purpose of the reverse biased diodes on the OPT/Cathodes as in
this Fender circuit?
http://www.schematicheaven.com/fende...er_60_rack.pdf
I need to replace a faulty one and am having difficulty sourcing the part
Fender use (R3000). Does this need to be a specific type of diode or can I
make up the 3kV diode required using standard 1Kv rectifier types?
The diodes prevent the anodes ever swinging below 0V when no load ins
connected and the
volume is turnd up.
Without the diodes, the OPT primary peak signal voltage can be up to
say +2,000V on one side, and -1,000V on the other OPT side.
This can cause arcing in the OPT and the windings to fuse.
If you wish to use alternative diodes, i suggest 3 seriesed IN5408 which
are each PIV rated for 1,000V,
have 3amp rating, and you should have 1M resistances across each diode.
Then the voltage max at one of the OPT can only be +1,000V and -2.1V at
the other,
and arcing won't happen.
Patrick Turner.
Thanks,
Gareth.