[78-L] When is a microgroove not a microgroove?

[David Lennick]

I have 4 7-inch 78s pressed (uncredited) by Decca, given as premiums by the 
Quaker Oats Company or something like that..the theme and 3 stories in the 
Sergeant Preston of the Yukon series, issued in 1952. You would think they were 
microgroove, but a .7 stylus gives a very hissy output..I thought this was poor 
pressing material, but I tried a 2.0 mil truncated elliptical stylus and the 
sound was perfect. Discs are near mint, so this doesn't seem to be a matter of 
the discs having been chiseled out. How come this, how come?

dl