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B&K 467 and triode tubes

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B&K 467 and triode tubes

Post by Cathovisor » Sun Dec 28, 2014 2:38 am

Whilst repairing my B&K 467 (all the 620k resistors used in the Set G2 circuits were way out of tolerance) I came across something which intrigued me, so I'll ask here:

Has anyone ever tested a monochrome triode tube with one of these testers?

The reason I ask is this: some of the older testers (e.g. the Radar ones) work by applying a potential between the cathode and the grid and measuring the current flow from cathode to grid and first anode, frequently with these latter two electrodes strapped. From memory, the original Radar tester applies about +100 or so volts limited to 250uA, whilst the later model 202 seems to apply about +30V to the grid and about +350V to the anode connection, again limited to 250uA. These voltages are all measured w.r.t. the cathode, btw. So with a triode gun you'd just be measuring current flow between the grid and cathode, with the grid acting as an anode.

The thing is, the B&K 467 supplies about -50V to the grid, and up to +530V to the A1/G2 connection. So... with a triode tube, where you'd just be drawing a current between cathode and grid... it can't possibly work, as the grid is negative w.r.t. cathode?

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