[Johnson] Tube Designation

[David C. Hallam]

Pete,

I can't seem anything one way or the other.  Right now the Pacemaker is a
work in progress.  When I am finished refurbishing maybe I will run some
tests.  I can try a 12AT7, ECC-81, 6201, and any other MilSpec variants I
can get my hands on and look the carrier and side band suppression on my
spectrum analyzer.

David
KC2JD/4

> -----Original Message-----
> From: johnson-bounces at mailman.qth.net
> [mailto:johnson-bounces at mailman.qth.net]On Behalf Of Peter Markavage
> Sent: Tuesday, April 22, 2008 12:57 PM
> To: Johnson at mailman.qth.net
> Subject: Re: [Johnson] Tube Designation
>
>
> One would have to check the spec differences between the ECC-81 and 12AT7
> but I would suspect the electrical and mechanical characteristics of the
> ECC-81 are probably tighter between ECC-81'a then "off-the-shelf"
> 12AT7's. Since you're dealing with a balanced modulator, you would want
> the tube characteristics to be as close to each other as possible. I
> replaced my 12AT7's in the balanced modulator of my Heath SB-10 years ago
> with 6201's for better carrier suppression on both upper and lower
> sideband.
>
> Pete, wa2cwa
> http://www.manualman.com
>
> On Tue, 22 Apr 2008 10:38:55 -0400 "David C. Hallam"
> <dhallam at rapidsys.com> writes:
> > Here's a question for the experts.  In the Johnson Pacemaker,
> > several
> > 12AT7's are used.  On the schematic the phase inverter is designated
> > as a
> > 12AT7 but the balanced modulators are designated as ECC-81.  I
> > always
> > thought the ECC-81 was just the European designation for a 12AT7.
> > Why did
> > Johnson use a different designation for these?  Is there a
> > difference?
> >
> > David
> > KC2JD/4
> >
> >
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> >
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