Special Tube??

[Ray Allen, W2KBR/3]

Heath Clan:
  Trying to bring a 110A up on line and I note in the manual that a
6AZ8 "with the painted tip must be installed at at V5"

There are 2 other 6AZ8s on board w/o painted tips.  And Heath gave the
painted guy it's own part number...

Anybody know why Heath wud do this??  And by the way, anybody got any
6AZ8s and are the 6DS4 Nuvistors still available? or a replacement?
Many thanks, 73
Ray Allen W2KBR/3
8303 Grainfield Rd,
Severn, MD.,21144-2331