Type of tube in SB-301 LMO?

[Stewart Lyon]

Hi gang,
I checked four LMOs from various vintages that I have and they used
either a 6BZ6 or 6CB6. These tubes are pinned out the same and their
other characteristics are similar so it probably wouldn't matter which
one you used. They have the "7CM" base.  The 6AU6 is based "7BK" which is
differant in that the supp. grid and the cathode are switched. You can't
sub one type for the other unless the cathode and suppressor are tied
together in the wiring ( which RCA recommends even though it's never
done).

To figure out which tube your LMO is wired for, I recommend that you
measure the resistance to ground of pins 7 and 2. If 7 is zero and 2 is
around 50 ohms, then its a 7CM (6BZ6,etc).  If 2 is zero and 7 at 50 ohms
then it's a 7BK -- 6AU6.

Eddy -- maybe that's why your LMO is so drifty!! You might have the wrong
tube in there.

Bob -- good luck on getting your license and please let us know here when
it happens so we all can give you a "welcome aboard".

73, Stu -- W6CUX.


On Sat, 9 Jan 1999 13:00:04 -0500 Dick Blaney <wb8mhe at BRIGHT.NET> writes:
>I believe I read an article in an old QST (about '73 or 74) about
>stabilizing the  '301 VFO, by putting regulated DC on the heater of
>the 6AU6.  I was surprised, since my '401  uses the 6BZ6, and is of the
>same vintage.  Anyway, as an oscillator, the difference probably would
be
>kinda "nano".  As usual, I could be wrong, as I usually am.
>73 de
>Dick, WB8MHE
>wb8mhe at bright.net
>
>-----Original Message-----
>From: Edward Swynar VE3 CUI <gswynar at DURHAM.NET>
>To: HEATH at LISTSERV.TEMPE.GOV <HEATH at LISTSERV.TEMPE.GOV>
>Date: Saturday, January 09, 1999 11:54 AM
>Subject: Re: Type of tube in SB-301 LMO?
>>I know my SB-300 receiver & SB-400 transmitter BOTH have a 6AU6 in
>the LMO---I understand, however, that later versions of these rigs
>switched over a 6BZ6...?
>>I'm sure someone on the reflector has a actual '301, & can speak with
>more authority than me on the subject...
>>
>>73, de Eddy VE3CUI - VE3XZ
>>----------
>>> From: Bob Knight <bob at HIGHFIBER.COM>
>>> To: HEATH at LISTSERV.TEMPE.GOV
>>> Subject: Type of tube in SB-301 LMO?
>>> Date: January 8, 1999 5:21 PM
>>>
>>> Hi - I am in the process of resurrecting my father's ham equipment
>with an eye to getting a ticket. I have the manuals on order, but want
>to test  the tubes. The existing tube in the LMO has its type
obliterated.
>Could some kind soul tell me the type for it?
>>>
>>> Thanks in advance,
>>> Bob

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