[Johnson] Tube Designation

[jeremy-ca]

I would suggest using a transconductance tube tester and pick tubes with 
both sections being as closely matched as possible.

You can also build a simple test jig to do similar by looking for equal 
plate currents with identical grid voltage. The tube curves in the tube 
manuals can assist in this.

Carl
KM1H

----- Original Message ----- 
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "Peter Markavage" <manualman at juno.com>; <Johnson at mailman.qth.net>
Sent: Tuesday, April 22, 2008 1:21 PM
Subject: RE: [Johnson] Tube Designation


> 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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>
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