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

Subject: Re: [Amps] Gassy Tubes/Technology Museum looking for artifacts
From: Karl-Arne Markström <>
Reply-to: Karl-Arne Markström <>
Date: Fri, 27 Jul 2007 13:13:44 +0200 (MEST)
List-post: <>
It appears that the date quoted on the German web-site for the 1625 was 

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 
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.
appears to be somewhat "skinnier" than the regular 807. If this may 
have affected the VHF performance is uncertain.



----Ursprungligt meddelande----
Datum: Jul 27, 2007 11:20:22 AM
Ärende: Re: [Amps] Gassy Tubes/Technology Museum looking for artifacts

>Wild guess: to prevent plugging a 6.3v filament tube in a 12.6v 
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. 
Peter G3RZP
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