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Type 6A3 was the American answer to the British type PX4 and has very similar characteristics and performance, although differing in filament voltage. Both types deliver around 3.5 Watts when used at 250 V HT.

Type 6B4G is the same valve but fitted with an IO base cap.

There is also a type 2A3 which was similar except for filament rating (2.5 V, 2.5 A). Both versions thus consume 6.25 W which is rather more than the 4 W (4 V, 1 A) consumed by most PX4s.

The 6A3 was also made with two triode sections wired in parallel. The practice of wiring two valve assemblies directly in parallel, without 'stopper' resistances, risks the possibility of low-level parasitic oscillation in push-pull mode at very high frequency (as many experimenters have discovered!). We are not aware that the 6A3 contained integral anti-parasitic 'stoppers'. Perhaps the gain (μ = 5) was too low to support oscillation.

Although at one time quite widely used (often in pairs) in the US, the 6A3 was never the equal of the PX4 and never achieved cult status.

This exhibit has no identification but the wording and style of lettering on the underside of the base match that used by National Union. The first 2A3 and 6A3 types had two triode sections connected in parallel. It is believed that the single triode version came later. This exhibit is believed to be the 6A3 but until tested we cannot be certain.

The anode seen side-on. Note that the main electrode supports are fixed to a collar round the pinch tube for maximum rigidity.

Looking into the top mica, the grid can be seen to be spaced widely from the filament.

The coated filament ribbons, support hooks and tension springs that are fixed to the top mica.

The classic envelope is 48 mm in diameter and, excluding the UX4 base pins, is 136 mm tall.

References: Private communication, data-sheet & ⁴⁰⁴⁰. Type 6A3 was first introduced in 1940. See also 1940 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.