Rich says:
>? What is the Mu of the tube, Tom.
The data sheet doesn't give it. It does give ra and gm, from which I work
out
mu = 9.
I'll stick my neck out now:
This is a very bad choice of tube for RF GG service. It is rated as an audio
tube;it has four cathode pin connections and one grid pin connection, plus
the centre spigot, so 'grounding' the grid correctly at higher frequencies
will be difficult. It requires the grid to be floated at 100 volts or more
negative to cathode; it has insufficient mu to be a good grounded grid
stage, and insufficient grid dissipation capability to be run without some
very good protection circuitry. ALC might save the grid, but will almost
certainly lead to very bad intermodulation products, unless the grid supply
is very 'stiff'. There are no RF ratings for this tube, and the absolute
maximum plate voltage is 1800 volts. The listed 'output' capacity for
grounded cathode (1pF) suggests that it could well have stability problems
on the higher bands (21MHz and above)
OK Rich, Tom, any comments?
73
Peter G3RZP
> ----------
> From: Rich Measures[SMTP:measures@vc.net]
> Sent: 27 July 1999 23:22
> To: W8JI@contesting.com; amps; ohashi
> Subject: Re: [AMPS] 3CX300A1 for AB1 GG
>
>
>
>
> >
> >> You are right if no ALC is used. My idea assumes 1-10 mA grid current
> >> (yes, it is little bit AB2), but ALC reduces driving power from the
> >> excitor, resulting total IMD is not so bad. Remember 6146 AB1 GC in
> KWM-2,
> >> same thing.
> >
> >First, ALC is not that fast. Most rigs can't even keep up with
> >themselves, let alone a loop from an external PA.
> >
> >Second, any grid current will perturb grid voltage unless the grid
> >comes from a supply with low esr and good dynamic regulation.
> >
> >Third, you are locked into cathode drive without complex circuitry.
> >
> ? What is the Mu of the tube, Tom.
> >
> >73, Tom W8JI
> >w8ji@contesting.com
> >
> >--
> >FAQ on WWW: http://www.contesting.com/ampfaq.html
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> >
>
>
>
> Rich...
>
> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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