SB 301

[Mark V. Johnson]

Glen,
Its with some hesitation that I question your technical wisdom as I've
always read your posts with great interest over the years and have
learned a many things.
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. According to my RCA tube manual, the
6CB6 and 6BZ6 have the same pinouts, the same filament voltages and the
same filament current draw. The two tubes should be interchangable as
far as filament voltages go. I'm not sure I see your point on this one.
As I say Glen, I have much respect for your technical wisdom but  I
can't see your point on this one  hihi..

Respectfully

Mark V. Johnson VE3DJU/VE3DDI

Glen Zook wrote:

>My SB-301 and my SB-110A use the 6BZ6.  My SB-401
>(which uses exactly the same LMO as the SB-301) uses a
>6CB6.  It really has to do with the "series-parallel"
>arrangement that Heath uses in their different models
>for the heaters.  If you replace the 6BZ6 with a 6CB6
>you will have problems in both the SB-301 and SB-110A
>because the other 3 tubes that make up the
>"series-parallel" operation will not have the proper
>voltage drop across them.  The same thing happens when
>you replace the 6CB6 with a 6BZ6.
>
>The schematic of the LMO is the same in the SB-301,
>SB-401, and the SB-110A manuals (at least in my
>manuals).  However, it does make a difference in which
>tube is used in what equipment.
>
>Thus, you MUST use the 6BZ6 in the SB-301 and you MUST
>use the 6CB6 in the SB-401 even though they use
>identical LMOs.
>
>Glen, K9STH
>
>
>--- Stanley White <swhite at CA.INTER.NET> wrote:
>
>SB 301 users,
>
>In the main Shematic it says to use a 6BZ6 in the LMO
>and in the LMO Shematic on page 95 it says to use a
>6CB6..I wonder which is the proper one to use.????
>
>
>=====
>Glen, K9STH
>
>Web sites
>
>http://home.comcast.net/~k9sth
>http://home.comcast.net/~zcomco
>
>
>
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