[Hallicrafters] Short metal tube mystery

[mikeqrpfun at aol.com]

Hi folks,
My long time ham buddy (W6LPU) and I have been recently sharing SX-28 stories and would appreciate some insight from you experts. I recall as a teenager that my SX-28 housed small non-OEM metal tubes in the center shielded RF section. I recall they were electrically equivalent replacements to the ubiquitous 8 pin OEM octal 3" tall metal tubes (like the ones in my BC-348-Q) but these puppies were only about an inch tall with a slight dome on top.

They supposedly offered better performance than their taller brethren. My buddy isn't resonating with my recollection thinking instead I was recalling "loctals" that have a very short distance between the pins and the elements so that they could be used in the VHF spectrum. He said his SX42 uses them saying they were pretty much duplicates electric-wise of the 6SXX series except they were labeled 7XXX. 
 
Seems this same good old buddy gave me one of his SX-28A receivers a year ago that I am getting ready to restore and would greatly appreciate you fine folks clearing my"brain fog" and forward your recollections of this mystery tube series and perhaps some part numbers that I so vividly recall. 

73 and thanks in advance,

Mike 
WB6UTW