[AMRadio] TH vs TL


John Coleman jc at pctechref.com
Sat Feb 23 16:47:48 EST 2008


I ran 304TLs in push-pull class C awhile back.  Required a lot of drive Just
about all the 32V3 could due.  I ran 500V of Grid Leak Bias at about 160 ma
of grid current for the pair.  At 1KW DC input using 1700Volts on the plates
I got a little over 800 Watts out to the dummy load.

I used 304THs for awhile in the circuit because of the much reduced drive
requirements got a little less output, and a little more color on the plates
but it modulated the same with good symmetry.  Those are the only
applications where I have compared the TL and TH.

John

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of W2INR
Sent: Saturday, February 23, 2008 3:16 PM
To: w2inr at amfone.net; Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] TH vs TL

Make that bias voltages, from the specs it looks like the drive will be 
similar in Class C

W2INR wrote:
> The only differences will be drive and bias voltages. The performance 
> will be the same once dialed in.
>
>
>
> G
>
> Brett Gazdzinski wrote:
>> 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.
>>
>> Brett
>> N2DTS
>>
>> ----- 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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