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G6Tanuki · 12th Feb 2021, 6:34 pm

Yes, the "W" variants are either ruggedised versions of the standard variety, or are standard-ones of a type which was deemed sufficiently-rugged-as-standard but which have been subjected to additional QA checks to confirm they meet the required spec.

Brimar had another thing - some of their top-spec valves were deemed "Trustworthy" and carried a yellow flash-symbol a bit like the Star Trek logo with a capital "T" in the centre. I've got some 6AL5 double-diodes so marked.

There is some evidence to support the additional quality of W-marked valves: in times-past I built a free-running local-oscillator for a HF receiver which used a 12AT7 as oscillator-and-cathode-follower. In tests I found the 12AT7W-version was significantly faster in becoming (relatively) drift-free after switch-on.

A 12AT7WA - the 'controlled warm-up' version - was even better!

12th Feb 2021, 6:34 pm	#5
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: 6SK7 and 6SK7W Yes, the "W" variants are either ruggedised versions of the standard variety, or are standard-ones of a type which was deemed sufficiently-rugged-as-standard but which have been subjected to additional QA checks to confirm they meet the required spec. Brimar had another thing - some of their top-spec valves were deemed "Trustworthy" and carried a yellow flash-symbol a bit like the Star Trek logo with a capital "T" in the centre. I've got some 6AL5 double-diodes so marked. There is some evidence to support the additional quality of W-marked valves: in times-past I built a free-running local-oscillator for a HF receiver which used a 12AT7 as oscillator-and-cathode-follower. In tests I found the 12AT7W-version was significantly faster in becoming (relatively) drift-free after switch-on. A 12AT7WA - the 'controlled warm-up' version - was even better!