Just switched on the 300B amp and after about 30secs the rectifier started arcing, lasted about one sec followed by one very quick arc and then seemed to be ok.
It’s a new JJ GZ34 and it arced low down near the base rather than in the plates.
Should this happen on a new GZ34? read it can be down to high input capacitance on the supply?
Rectifier arcing is usually down either to them being asked to pass too much current (something downstream’s gone awry and is drawing too much current) or because they’ve got some gas in them somehow (the glass is micro-cracked, or a gas bubble trapped in a spot-weld has burst). As Pete says, the first cap after the rectifier is supposed to be 60uF max, but that’s assuming the rest of the circuit is operating close to max current and voltage. If the rest of the circuit can be guaranteed to be gentle on the rectifier then it is possible to get away with a bit more than 60uF. It’s not good practice though.
Arcing at the bottom of the valve can be due to a bit of debris dropping out of the main structure and bridging across the wires where they feed through the glass base.
The 5R4Wxx datasheet specifies a very low first capacitor - just 4uF - although experience says you can get away with more. They have a big forward voltage drop though, so you’ll be under-running the 300Bs with a lower HT voltage.
Without knowing the circuit it’s difficult to be sure.
There are plenty of designs that aren’t very good and don’t observe specs, so I wouldn’t necessarily trust recommendations without being sure. Especially if risking nice vintage tubes. (New tubes are mostly utter crap anyway)
As Graeme says, the voltage drop will be significantly higher with 5R4 meaning a different operating point and less power. It will sound different for sure.
I’m specifically using crappy old shuguang 300B and new JJs as I’ve read his build quality can be a bit crap so didn’t want to risk anything nice or NOS
This was my first thought on seeing it was a new rectifier, albeit not a Russian one at least…
Short-lived and unreliable rectifiers are my #2 () reason for giving-up on all-valve gear - sick to fucking death of watching them fritz-out on startup.
Only exceeded by the misery of suicidal SETs… (#1 reason)
The difference is whether the filter after the rectifier is CLC or just LC - the third and fourth cases here (CLC is a pi filter though, not a pie one !):
Nope, CLC (plus whatever, second C is off the right of the drawing). Depends if you have enough spare voltage to add resistance in from the transformer
(or prior to the cap) to limit the current that can flow.