[Boatanchors] 6146 A or B ?

[Glen Zook]

Penta did make 6146B/8298A Tubes.  The SB-101 is generally very unhappy with the 6146B/8298A or 6146W tubes (with a code date of mid 1965 or later).

Most of the Heath SB-Line equipment put the heaters ("filaments") of the final amplifier tubes in series.  If you change this to parallel you can definitely use the 6883 or 6883A/8032 tubes.  However, make sure and put a label on the final amplifier cage telling that this modification has been made.  Otherwise, someone might replace the 12 volt tubes with the 6 volt version.

Glen, K9STH

Website:  http://k9sth.com


--- On Mon, 12/21/09, Drew P. <drewrailleur807 at yahoo.com> wrote:

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...