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G6Tanuki · 30th Jul 2019, 6:53 pm

I always thought that the first B7G valves were the 9001/9002/9003

http://www.r-type.org/exhib/aab0161.htm
http://www.r-type.org/exhib/aaa0254.htm
http://www.r-type.org/exhib/aaa0253.htm

which were essentially Acorns re-engineered to avoid the seal-cracking-and-loss-of-vacuum issues that beset the Acorns.

The 717A

http://www.r-type.org/exhib/aab0012.htm

was also an intriguing interim valve - though it used an Octal base it minimised leads-inside-the-envelope issues by turning the electrode assembly on its side so it could be fitted as close as possible to the base.

Equally, I have always liked the 6AK5/EF95

http://www.r-type.org/exhib/aaa0122.htm

that was used in a number of 1940s/1950s-era civilian-air-band [100-150MHz] receivers and some similar-timescale civilian mobile-radios. Small, efficient, alas it was not good for use in VFOs because of the suppressor-grid-to-cathode strapping.

30th Jul 2019, 6:53 pm	#43
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: EF91 to EF80 I always thought that the first B7G valves were the 9001/9002/9003 http://www.r-type.org/exhib/aab0161.htm http://www.r-type.org/exhib/aaa0254.htm http://www.r-type.org/exhib/aaa0253.htm which were essentially Acorns re-engineered to avoid the seal-cracking-and-loss-of-vacuum issues that beset the Acorns. The 717A http://www.r-type.org/exhib/aab0012.htm was also an intriguing interim valve - though it used an Octal base it minimised leads-inside-the-envelope issues by turning the electrode assembly on its side so it could be fitted as close as possible to the base. Equally, I have always liked the 6AK5/EF95 http://www.r-type.org/exhib/aaa0122.htm that was used in a number of 1940s/1950s-era civilian-air-band [100-150MHz] receivers and some similar-timescale civilian mobile-radios. Small, efficient, alas it was not good for use in VFOs because of the suppressor-grid-to-cathode strapping.