Rectifier Tube Rolling in a Modwight LS 36.5DM

@robergerman
"I don't know the tube complement the LS36.5 DM uses. Just thought I'd list the most common preamp tube types! "
He listed it in his opening -  6H30 DR . 

I have done some research. Apparently the 6CG7/6FQ7 will work as a substitute. Same pin-outs, similar GM and capable of 250 volts/plate. Good quality US-made ones are available for a lot less than the pricey 6N30's (correct designation). I use them in my NYAL Moscode 150.

The Cyrillic "H" is actually "N" - and is pronounced that way! I can read and speak Russian!

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. "

@facten : The 6N30 and the 6CG7/6FQ7 are both 9-pin bases. I haven't yet looked at basing diagrams so I can't say for certain that they are identical. I suspect they are! And the Russian tube is likely a copy of the 6CG7/6FQ7 type dual-triode. Not some secret "super" tube!