On Wed, 27 Jan 1999 22:32:49 EST Skip S Isaham <nospam4me@juno.com>
writes:
>
>? I know only too well that, in HF service, tetrodes with >50-ohm
>grid
>terminations are more likely to turn into surprise oscillators if they
>
>are not neutralized.
>
>So how is the grid termination resistance value selected?
>I've seen amplifiers with 50 ohm termination values going higher.
>With
>higher resistance values, I've seen toroid matching transformer
>networks.
>
>Is there a guideline for the selection of a grid termination resistor,
>or
>is it done by method ?
>
>thanks
>skipp
>nospam4me@juno.com
I've run up to 600 Ohms with various glass tetrodes but 200-300 is more
the norm. Real squirelly tubes such as the 8122 series are happy at 50
Ohms.
The 1:4 toroid stepup is ideal when you are drive/voltage limited with
better behaved tubes such as most of the Russian tubes I have played
with.
In all cases I highly recommend full attention to screen bypassing by
using a full circumference bypass ring/socket when possible AND directly
grounding the cathode with the lowest inductance you can come up with.
73 Carl KM1H
>
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>
___________________________________________________________________
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