New JTM45 build blowing fuses.......

[pompeiisneaks]

Provided you use a GZ34 but not standby, fast blow are fine for the HT fuse.
If an F500mA is blowing, there’s an actual issue.
Time to dust off your light bulb limiter.

yes, I keep my standby permanently on and just use the main power switch. I remember reading about the poor design of the standby on these amps years ago so have always done that. I can't remember the actual technical reason though. Perhaps @pdf64 can fill me/us in on the reason


M

I can answer that pretty easily.

The standby switch "Can be implemented in a non harmful way' but is never needed at all. The bad idea as I understand it came from people copying the standby switches required for tubes that operate above 1.5kV that can have cathode stripping or cathode poisoning effects/impacts. if a tube operates below that level (Every single guitar amp ever) then a standby switch is an additional cost with no benefit.

Many times the standby switch is setup so that it forces inrush current into the amplifier in an unsafe, very rapid way, that does permanent damage worsening over time to components in the amplifier.

With tube rectifiers the startup is always nice and gradual because as the tube warms up, it's output voltage slowly increases, so in those amps it often made things worse, because people would leave it on standby until the rectifier was at full warmth and suddenly send in current at an extremely high rate stressing the amplifier.

Here's a nice long read with a lot of the facts: http://valvewizard.co.uk/standby.html

~Phil