rocket blowing fuses....

[redshark]

Why does my rocket blows a fuse once a week?
It's not a constant problem is just a random situation, once replaced it works fine for a few days and suddenly blows the fuse, I replace it and good until it does it again....

Anybody had a problem like this before?

[Gibsonman63]

Sounds like hard one to diagnose. Obviouisly you are exceeding the current rating of the fuse when it happens. I don't know if I can be much help, but maybe I can trigger something.

Some silly questions:
Do you have the correct size fuse installed and is it a slo-blo type fuse?
Does anything playing-wise affect it? The low notes take the most power.
Any chance of an intermittant short?
Voltage dips? Is it possible that a bad filter cap is causing this?
A shorted power tube will take out the fuse every time. Maybe try some different power tubes.

If nothing else, you could pull the tubes and take all the voltage measurements and then do it again with the tubes installed. When in doubt, gather data.

[M Fowler]

Unsuspecting loose wire such as cold solder joint or missed solder joint lead wrapped around turret but not soldered

[redshark]

I've been watching carefully any signs of a cold solder joint, actually resoldered a couple but all the voltages make sense. Amp is very quiet and plays good for days. Then at some point just blows the fuse. Replace it for a new one and runs for days until it decides to blow the next fuse. Never 2 fuses same day. Weird!!!!!! Yes fuses are 2 amps slo-blo.

[MCK]

is very quiet and plays good for days. Then at some point just blows the fuse. Replace it for a new one and runs for days until it decides to blow the next fuse. Never 2 fuses same day. Weird!!!!!!

Sounds like my wife. Just get used to it!

[Cliff Schecht]

is very quiet and plays good for days. Then at some point just blows the fuse. Replace it for a new one and runs for days until it decides to blow the next fuse. Never 2 fuses same day. Weird!!!!!!

Sounds like my wife. Just get used to it!

My Express did this too until I switched from fast blow to slow blow fuses. The high inrush current for the filaments was blowing the fast fuses.

[fishy]

Rectifier tube
Do you have a solid state plug in you can try or a different rectfier tube.

[redshark]

If it's actually the rectifier that will suck cause this is a mullard GZ34. I have a japanese realistic that was there and I have as a backup so maybe I should put the japanese and keep it there for weeks.

[TheGimp]

What are the conditions when the fuse blows?

At power on to heaters?

When switching on from Standby?

Are you driving it hard when the fuse blows, or does it blow while running but not jamming?

[tubedogsmith]

Rectifier tube
Do you have a solid state plug in you can try or a different rectfier tube.

Most likely correct.

[redshark]

It blows when I turn the amp on. It has never blown when I hit the standby on, once amp is on is good. It only blows with on off switch and not everytime, is like every 10 times. Weird but I'm suspecting the rectifier tube.

[TheGimp]

The Rocket has more tubes than any other TW by virtue of the fact that it is tube rectified. I suspect that all the tube filament in-rush current when cold combined with the cap charging current as the rectifier is comming on line is exceeding the fuse rating.

A bad GZ34 would compound this issue.

If swapping the rectifier tube does not fix it, another option is to add a NTC thermistor in the hot AC after the switch and fuse to limit in-rush current.

[PlinytheWelder]

The Rocket has more tubes than any other TW by virtue of the fact that it is tube rectified. I suspect that all the tube filament in-rush current when cold combined with the cap charging current as the rectifier is comming on line is exceeding the fuse rating.

A bad GZ34 would compound this issue.

If swapping the rectifier tube does not fix it, another option is to add a NTC thermistor in the hot AC after the switch and fuse to limit in-rush current.

The NTC in-rush limiter would probably work and you could get fancy and bypass it with an extra pole on the stand-by switch....

[redshark]

My 2 rectifiers were tested and they test fine so should I just use a 3amp instead of the 2 amp and forget about it? checking the schematic nothing else can be wrong in that scenario, just the rectifier circuit because is the only thing before the standby, if it was something else it would blow when the standby is on but is only on power on.

[Structo]

How old is the power switch?

It could be arcing.

Make sure you are using 2 amp slo blo fuses.

A fast acting fuse can't handle the in rush current.

Try a different rectifier tube if you have one.

It could also be a faulty reservoir cap, one of the 40uF caps right after the rectifier.