"Chris Jones" wrote in message ...

On 11/08/2016 23:54, Phil Allison wrote:
Chris Jones wrote:

http://www.andy-duke.co.uk/roost/Non...2006_05_14.png

Maybe when you replace the switch, rewire it in series with the HT
fuse - that should allow arcs to extinguish at switch off.


.... Phil


Also, if you can get a 2-pole switch that fits ok, then wiring the two
sets of contacts in series ought to improve the ability to extinguish
the arc, (for a given contact separation etc.).


** If you look at the schem, the HT fuse is in the rectifier ground path
where the voltage and current levels drop to zero at twice the supply
frequency.

So for a couple of mS each 10mS, there is not enough of either to sustain
an arc.

Yes, I noticed that. It is much better than the original arrangement. If
C23 and C24 are in good condition and the B supply rail doesn't get
shorted, then the fuse (and new switch) should only be carrying current
for a quite small fraction of the time, so arcs should extinguish well,
perhaps even better than with a resistive load on AC.







Thanks Chris and Phil, that's very interesting.

Why wasn't this practice adopted decades ago? Were Fender (Bassman) really
that clueless?
Beggars belief.



Cheers,

Gareth.