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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 12th Feb 2021, 4:57 pm   #1
ribbonmicsrus
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Default 6SK7 and 6SK7W

Can anyone tell me the difference if any between a 6SK7 and a 6SK7W, I cannot find any substantial data on the W version.

Cheers
Andy
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Old 12th Feb 2021, 5:07 pm   #2
paulsherwin
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Default Re: 6SK7 and 6SK7W

A 6SK7 is a 6K7 without a top cap. I think the 'W' just means it's military.
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Old 12th Feb 2021, 5:16 pm   #3
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Default Re: 6SK7 and 6SK7W

Supposedly, the 'W' stands for War (!), it seems to have been a post-WW2/'50s designation applied to quite a few valves supplied for US military use- 6L6, 6AL5, 6AK5, 6BA6, 6BE6 etc. often turn up with a 'W' suffix. I think that it often means a ruggedised version with detail production changes to resist shocks and vibration, rather than noticeably improved electronic performance. The 6SK7, a late-'30s modest-mu IO pentode, was getting a bit old hat in the post-war era, but this version probably illustrates that there was still a great deal of legacy electronics in the US inventory.
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Old 12th Feb 2021, 5:27 pm   #4
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Default Re: 6SK7 and 6SK7W

Great, many thanks for that, just been given some so that has put my mind at rest, yes I have a few 6K7s and for a new project aesthetically not appropriate.

Andy

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Old 12th Feb 2021, 5:34 pm   #5
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Default 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!
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Old 12th Feb 2021, 6:43 pm   #6
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Default Re: 6SK7 and 6SK7W

Quote:
Originally Posted by turretslug View Post
Supposedly, the 'W' stands for War (!), it seems to have been a post-WW2/'50s designation applied to quite a few valves supplied for US military use- 6L6, 6AL5, 6AK5, 6BA6, 6BE6 etc. often turn up with a 'W' suffix. I think that it often means a ruggedised version with detail production changes to resist shocks and vibration, rather than noticeably improved electronic performance. The 6SK7, a late-'30s modest-mu IO pentode, was getting a bit old hat in the post-war era, but this version probably illustrates that there was still a great deal of legacy electronics in the US inventory.
Another interesting thread!
I was thinking about the "Y" suffix on some metal valves. It meant a low loss mica filled yellow molded base. They were intended for high frequency use. 6SB7Y and several others. The "Loctal" valve was also intended for that application. And then, there's the Acorn valve!
Dave, USradcoll1
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Old 12th Feb 2021, 6:57 pm   #7
ribbonmicsrus
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Default Re: 6SK7 and 6SK7W

Thanks Dave and everyone, I have a few Acorn valves still, 954 and 955.

Andy
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Old 13th Feb 2021, 10:12 am   #8
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Default Re: 6SK7 and 6SK7W

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Originally Posted by usradcoll1 View Post
Another interesting thread!
I was thinking about the "Y" suffix on some metal valves. It meant a low loss mica filled yellow molded base. They were intended for high frequency use. 6SB7Y and several others. The "Loctal" valve was also intended for that application. And then, there's the Acorn valve!
Dave, USradcoll1
6SJ7Y with its mica filled base was notably used in the BC-221 heterodyne Frequency Meter. I restored the -AF version one of these many years ago and debugged it with a standard 6SJ7. The eventual fitting of the Y improved a reasonably stable unit to a quite incredibly stable and accurate unit, quite good enough for amateur h.f. work even today (although tedious to use compared to modern digital's).

I love acorn valves ! As a youngster I played with the 954/5/6/7 and Marconi/Osram/MOV HA1 in various radio projects. I was particularly attracted to their tiny size, so also used them to make a very physically small audio amplifier - the only one attempted as far as I know. I gave up working with them when UHF valve holders became unobtainable at pocket-money prices (pre-Internet days).

Cheers, Marty
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Old 13th Feb 2021, 10:48 am   #9
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Default Re: 6SK7 and 6SK7W

The BC453B here has a yellow-base 12K8 in it, which struck me as curious with a valve that isn't expected to perform beyond 635kHz! (The metal "bottles" are all RCA-brand with similar font, so possibly original). Maybe it was specified for the HF versions and it was simply easier to load all receiver versions with one stock type.

There was a suggested "upgrade" for the AR88 series that involved replacing the 6SA7 mixer with a 6SB7Y, but I suspect that this was another one of the slightly straw-clutching attempts to make old-timer thermionic sets seem more attractive and "with it" as transistors inexorably muscled in as the '60s progressed.
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Old 13th Feb 2021, 5:31 pm   #10
usradcoll1
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Default Re: 6SK7 and 6SK7W

Quote:
Originally Posted by turretslug View Post
The BC453B here has a yellow-base 12K8 in it, which struck me as curious with a valve that isn't expected to perform beyond 635kHz! (The metal "bottles" are all RCA-brand with similar font, so possibly original). Maybe it was specified for the HF versions and it was simply easier to load all receiver versions with one stock type.

There was a suggested "upgrade" for the AR88 series that involved replacing the 6SA7 mixer with a 6SB7Y, but I suspect that this was another one of the slightly straw-clutching attempts to make old-timer thermionic sets seem more attractive and "with it" as transistors inexorably muscled in as the '60s progressed.
Regarding using a 6SB7Y in a Hallicrafters receiver, I mentioned it at a ham radio swap meet to make the set more stable and more sensitive on the highest band.
Hallicrafters made a SWL receiver, model S108, built in 1963 that used an identical chassis to a S40B, which was built in 1951. Same valve compliment, all metal valves! The cabinet and the appearance was modernized for the times.
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