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Re: [Amps] Gassy Tubes/Technology Museum looking for artifacts]

Subject: Re: [Amps] Gassy Tubes/Technology Museum looking for artifacts]
From: W2XJ <>
Date: Fri, 27 Jul 2007 11:42:20 -0400
List-post: <>
It was mentioned earlier in the thread that the 7th pin was to prevent
807s from being plugged in by mistake.

Karl-Arne Markström wrote:
> It appears that the date quoted on the German web-site for the 1625 was 
> wrong.
> In the 1942 edition of the "RCA Guide for Transmitting Tubes" that 
> went to press
> in October/November 1941 the 1625 was included and 
> was described as "Similar to 807 but has 12.6 V heater ... Especially 
> Useful in Aircraft Transmitters"
> So the 1625 was around before Pearl Harbor.
> Any reasons for RCA to choose the 7-pin base for the 1625 were not 
> mentioned, and they are probably buried deep into the sediments of 
> corporate logic. My guess is as good as anyone elses.
> Regarding the 8018, it seems to be an interesting variation of the 
> 807.
> I found some variants, one with a normal phenolic base but quoting a 
> higher transconductance than the "regular" 807, and two with ceramic 
> bases, the RAF VT-60 and VT-60A.
> The electrode system in the VT-60 shown at http://www.tubecollector.
> org/vt60.htm
> appears to be somewhat "skinnier" than the regular 807. If this may 
> have affected the VHF performance is uncertain.
> 73/
> Karl-Arne
> ----Ursprungligt meddelande----
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> Datum: Jul 27, 2007 11:20:22 AM
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> Ärende: Re: [Amps] Gassy Tubes/Technology Museum looking for artifacts
>>Wild guess: to prevent plugging a 6.3v filament tube in a 12.6v 
> socket?  
> Maybe 807's were also used in other applications in that era.<
> It seems a bit illogical, because  there were 6 and 12 volt octal 
> tubes with the same base connections - 6K7, 12K7, 6SG7, 12SG7 etc. 
> Further back, there were 2.5 volt and 6.3 volt tubes on the same UX 
> base - 2B7 and 6B7 come to mind. So why go to the bother for 1625s, 
> when they needed more metal for the two extra pins? And the quantity of 
> 1625s made meant that must have been a fair weight of brass for those 
> two extra pins.
> 807s were around pre war, and there was one of the early RAF VHF 
> transmitters used something called an 8018, which my father told me was 
> an 807 selected for more output at 120MHz - he actually instructed on 
> that equipment when he was in the RAF. He said it was awful speech 
> quality, using the device as a sort of linear with low level grid 
> modulation on the preceding frequency multiplier, and running grid 
> current in the 8018. 
> 73
> Peter G3RZP

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