[AMRadio] TH vs TL

Brett Gazdzinski Brett.Gazdzinski at verizon.net
Sat Feb 23 13:53:40 EST 2008

I don't think you will see any difference at all.

I used both as modulators, with the same results, and use 811 and 812
triodes in the push pull rig with the same results also.

Theoretically, the higher bias tubes work better in class C
but you cant hear or see any difference.


----- Original Message ----- 
From: "Barrie Smith" <barrie at centric.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Saturday, February 23, 2008 1:41 PM
Subject: [AMRadio] TH vs TL

I'm curious as to the difference in RF performance between the TH (as in 
250TH) and the TL (as in 250TL)  versions of older triode tubes.

Looking through the Eimac spec sheets for various old, glass triodes, the 
only real difference appears to be that the TL versions require higher grid 
bias in class C RF service.

I've used the TH versions of several of the older tubes a good number of 
times over a many year period, but I've only used the TL types in modulator 
service.  However, if there is no real difference in RF performance between 
the two in class C, I'm tempted to.

73, Barrie, W7ALW

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