GZ32 rectifiers for a quad amp

[Richard - F4VPR]

Originally Posted by Radio Wrangler

You'll find that transmitting valves have no getter. Because of the high voltages involved, the manufacturers didn't want the risk of vaporized metal being sprayed around and any getting onto any insulators.

So they were subjected to a diffusion pump to take them right down to a very low final pressure, and kept there for some time to allow outgassing to proceed before they were sealed off. David

But these surely did have a getter as a zirconium or titanium plating on their large graphite anodes that only operated with a high anode temp, IIRC at least 572B's and 4-400A's are strongly recommended by the makers to be run with heaters and preferably some quiescent anode current at lowered voltage for at least 10hrs for a new or 2 month out of service valve so the getter plating has a chance to heat and capture some of the gas thus alleviating the possibility of gas induced flash-over.

R.

[trobbins]

I'd side with Lucien's view of the small deposits on the top of the glass being tungsten from the heater at the top hair-pin. The heater would sit at hundreds of volts relative to glass, and would be the hottest metal.

They may have purposefully not coated that top bend region. If uncoated, that small section of heater may be visible at power on from 'heater flash', as there is no coating thermal mass to slow the dynamic temperature rise from in-rush current.

The sections of exposed heater wire at the base would be cooler due to the connecting tabs.