SB 301

[Glen Zook]

My manual for the SB-301 shows a series parallel
arrangement for the heaters as do the SB-401 and
SB-110A (which definitely use 12 volts on the
heaters).  I was going from memory on the heater
current because I do know that there was a problem in
the current draw between various tubes that are used
in the LMOs.

If the tubes have the same current draw then there
will not be any problems.  However, on those types
that do have a different current for the heaters there
can definitely be problems.  I ran into that with my
SB-110A when the 6BZ6 heater opened up.  At the time I
did not have any more 6BZ6 tubes and I tried different
tubes with the same base including those used in other
SB line models.  None of them worked.  One tube in the
series / parallel string glowed very brightly while
the other one didn't light at all.  Then I acquired
100 6BZ6 tubes from eBay and haven't looked back!

Glen, K9STH


--- "Mark V. Johnson" <mvjohn at sympatico.ca> wrote:

I'm looking at my SB-301 and it has the 6CB6. I'm
looking at the schematic for the SB-301 and all tube
filaments are connected in parallel. The schematic
does discern those tubes that are direct chassis
mounted (6AS11, LMO tube) vs those on the 2 circuit
boards, however, they are connected in parallel.


=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco



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