roberjerman - tubeworld contradicts your finding that the
6H30 DR
and
6CG7/6FQ7
are equivalents
" a 6FQ7/6CG7 is electrically similar to a 6SN7GT, but a 6FQ7/6CG7 has 9 pins versus 8 for a 6SN7GT "
and from fourwater
" To address this problem, the 6CG7 was created which simply put the 6SN7 elements into a 9 pin minature tube. The main difference is that the plates of the two sections are slightly closer together because of the narrow confines of miniature tube. They did add a twist though, since there were 9 pins available, they decided to add a shield between the two triode sections and bring it out on the extra pin. This was used to keep the two sections isolated, which can be especially useful for high frequency use. This made the tube slightly more expensive to make, so later the 6FQ7 was created which eliminated the internal shield. "
" a 6FQ7/6CG7 is electrically similar to a 6SN7GT, but a 6FQ7/6CG7 has 9 pins versus 8 for a 6SN7GT "
and from fourwater
" To address this problem, the 6CG7 was created which simply put the 6SN7 elements into a 9 pin minature tube. The main difference is that the plates of the two sections are slightly closer together because of the narrow confines of miniature tube. They did add a twist though, since there were 9 pins available, they decided to add a shield between the two triode sections and bring it out on the extra pin. This was used to keep the two sections isolated, which can be especially useful for high frequency use. This made the tube slightly more expensive to make, so later the 6FQ7 was created which eliminated the internal shield. "