[Johnson] Tube Designation

[Peter Markavage]

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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