[Amps] Designing the Cleanest Linear with RF Negative Feedback

[R.Measures]

On Dec 23, 2005, at 3:11 AM, Steve Thompson wrote:

>
>
> A few thoughts covering several recent posts:
>
> Stability with tetrode amps should not be a problem if you use ceramic
> tubes with the proper bases. More than anything, I think it's the lead
> length in glass tubes that brings problems.

For VHF and UHF amplifiers, I found this to be true, but for HF ones, 
to my surprise, things blew.  As I see it, whereas lanky glass-tubes 
can have VHF parasites, compact ceramic ones can have UHF parasites.  I 
think it's advisable to remember that at 300MHz, the output (anode) to 
input (cathode) feedback path in an 8877 has c. 5000-ohms of reactance, 
which is nothing to sneeze at with 4000v on the anode.
end.
>
> ...
> Steve
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org