6x4 valve arcing

[ben]

Just picked up a record player using said rectifier valve plus EL84 and ECC85. There was considerable arcing in the rectifier even after changing the mains filter can (which I thought might have been s/c). No sign that the valve is up to air, not milky. Was just wondering how common this is with these valves as I'm unfamiliar with 'em.

I am fairly sure this 125v unit has been plugged in to 230v, there is a tell tale smell and slight wax leak on the transformer. So it's possible the valve was damaged.

Will try a silicon diode rectifier + series resistor lashup and post back. I was just curious.

[Maarten]

Could it be that the transformer now has a partially shorted primary winding?

[Robert Gribnau]

Or perhaps a deteriorated cathode to heater insulation?

[GrimJosef]

My experience is that rectifiers may survive one or two small arcs, but anything more than that and they are irreparably damaged. Bits of cathode coating can be blown off and both electrodes can acquire arc craters whose sharp edges can induce further arcing. The 6X4 is a miniature device and, as such, not capable of withstanding very heavy abuse.

Cheers,

GJ

[Sideband]

The 6X4 (EZ90) is only rated at 60mA (similar to the EZ80). My experience with these little rectifiers has been good so they don't seem to be inherently unreliable. I've had several GEC radio's that use these and the originals have been fine some 60 years on. I have an HMV set that is 60 years old and still on the original.

Misuse is another thing though....probably depends on how much of an overload your 6X4 had to endure....

[ms660]

Max. repetitive peak anode current is 0.245 Amp, max. transient peak anode current is 1.1 Amps for 20ms, rectifiers are a bit fussy about their max. limits.

Lawrence.

[ben]

I have been running this one with a silicon rectifer and it's been fine. Fortunately, it doesn't look like it's been left on with 230v going into it, so I think that 6x4 valve was the only victim. Will probably leave as-is (the mod is easily reversible).

Spain was still using 125v AC mains into the 1970s in many areas, so players like these turn up quite often. Of course if someone born later than circa 1970 may happen on one, feels curious and just plugs it in, there will be fireworks. I dread to think how many vintage items have been harmed by this. I always label such items with a warning about the voltage for future scenarios.

Thanks again for the info.

[vidjoman]

Did you mean this - Just picked up a record player using said rectifier valve plus EL84 and ECC85. Or should that be ECC83? The pin outs are different. So if someone has fitted an 85 this might cause problems.

[ben]

To be honest, I could only read the lettering on the rectifier and the EL84. The cct diagram on Radio museum shows an ECC85.

[Nuvistor]

It’s a live chassis R/P even though it’s using 6 volt heater valves. I like the brochures that are on Radio museum, very 1960’s.