[Boatanchors] 6146 A or B ?

[Drew P.]

Glen Zook Wrote:

"GE specially "culled" a number of their 6146B/8298A tubes for Heath (primarily to use in the HW-101) that were not so "touchy" in terms of neutralization and so forth.  Those tubes were "cross branded" with the 6146A/6146B nomenclature.  They may have done a similar thing for other radio manufacturers."

My Heathkit SB-101 has a pair of 6146B's marked "Penta".  I don't think that Penta made small, almost-receiving type tubes like the 6146 family. So, these might be cross branded.  They have acted a little squirrelly, such as jumping suddenly to full output and high plate current with only a very small movement of the plate tuning control, this with very low drive so as to keep dissipation down when tuning. Turning the drive back to zero in this instance did not affect the aforementioned full output and high plate current - seems like oscillation.  I haven't gotten around to reneutralizing yet. 

Also, I ran transmit into a dummy load at 80 mA plate current, tuned to resonance, for a while.  By my calculations the dissipation should have been below that rated for the finals, yet one tube showed a fair amount of color and the other no color.  Methinks it may be time for a replacement pair.  Might as well get non-B tubes while I'm at it, avoiding potential for the problems about which you have eloquently written. Maybe 6883's with 12V heater wiring for the low cost motif...

Glen added:

"Now if you want to see some 6146 tubes with a real identity crisis you need to obtain some FADF marked tubes.  I have a couple in my "collection" of 6146 family tubes that are marked only FADF/USA (nothing else anywhere on the tubes).  The letters correspond to the number of the letter in the alphabet.  That is

F is the sixth letter so F = 6

A is the first letter so A =1

D is the fourth letter so D = 4

Therefore, FADF = 6146."

So, should I get a pair of FADF or FADF1? Can they be substituted with FADF2's?  (Snicker)

Drew