Maurizio Panicara wrote:
>>
>> That is not correct. There are many application that require
>> neutralizing a GG amp. It is easy, cheap, and very reliable when
>> done correctly.
>
>Using modern and good ceramic tubes, the neutralization in Gg
>applications is practically a complication and a waste of time. I never
>seen any neutralization in professional and broadcast Gg amplifier
>applications with 3cx800A7, 3cx1500A7, 3cx3000A7, 3cx6000 (YU148),
>3cx10000, 3cx15000, 4cx1000, 4cx5000, 4cx10000, 4cx15000 etc. etc.
>
To be fair, these are all tubes of modern construction with grid rings
and very short internal connections. Effective external grounding or
bypassing should (and does) avoid the need for neutralization for these
tubes, because the anode-cathode capacitance is very low indeed.
But the current discussion is about tubes with very long internal grid
connections. For these tubes, neutralizing should be a benefit.
It isn't quite a simple bridge neutralization network, because the
anode-cathode capacitance is not a single capacitor. It's actually a T-
network composed of anode-grid capacitance and grid-cathode capacitance
in series, shunted by the grid lead inductance to ground... and that's
before you add in the other parasitic inductances.
Even so, simple neutralization (capacitive feedback in antiphase) will
substantially decrease the output-to-input feedback on the band or bands
where the tubes are most frisky. If the bridge is balanced as accurately
as possible at the HF end of the range, the effects of the grid
inductance will become less important at lower frequencies.
Anyone care to try this with ARRL RD or SPICE? (It's early morning here,
with a full day's work ahead.)
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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