-150V is CUT -OFF bias
in AB1 or AB2 I use approx -65 V if I remember correctly.
If you use a 50 ohm grid swamping resistor, approx 50 Watts will do (I did
not calculate it).
John, ON4UN
----- Original Message -----
From: "Frank Goenninger" <frank_goenninger@t-online.de>
To: "R.Measures" <r@somis.org>
Cc: "AMPS" <amps@contesting.com>; <DF3KV@aol.com>
Sent: Friday, March 26, 2004 8:07 PM
Subject: Re: [Amps] Re: GU-84b: Drive power required for full power output ?
Hi Peter, Rich, & all the others on this list,
thx for replies. Having expose myself as mostly new to tubes and such, I
see that the GU-84b allows for -150V on the grid.
Given a 50 Ohm input circuit about 100V peak will be produced by 100W
drive power.
This would require to bias the grid at about -100V which is within
limits of tube parameters.
What would be the consequences out of this? Rich, you mentioned a
typical value of about -80V for the grid bias. Sorry, I still do not
have any suitable datasheet (and found none on WWW too)...
So my parameters for the GU-84b are:
Ua = 3000V (Anode)
Ug1 = -100V (Grid)
Ug2 = 375V (Screen)
What would be the resulting values for
Ia
Ig2
???
Thx for all the assistance so far!
73, Frank
On Fri, 2004-03-26 at 17:06, R.Measures wrote:
> >In einer eMail vom Do, 25. MÃrz 2004 18:21 MEZ schreibt
> >frank_goenninger@t-online.de (Frank Goenninger):
> >
> >>I initially intended to ask if about 1A of input current will be enough
> >>to really get reasonable power output?
> >>
> >>This comes from a simple calc from Pout of the TRX, which is about 100W
> >>producing about 1.4 A of current into 50 Ohms.
> >>
> >>Also, for this tube, what type of input circuit would you recommend when
> >>trying to cover all bands up to 30MHz ?
> >
> >Hi Frank,
> >
> >Since this is a tetrode it will be run without grid current,
> >the driver does not need to deliver current, just voltage.
> >Typically the grid is loaded with a 50 Ohm dummyload, into
> >which drive voltage developes without tuned circuits.
> >For the higher bands you probably have to compensate the high
> >input capacity with a small coil in parallel.
> >I guess you will need not more then 25W drive for full throttle.
> >
> â My guess is that with a 50-ohm termination, somewhat more than 25w
> will be needed to drive the grid up to the 0v point. The grid potential
> is typically -80vdc. 64w is needed to produce 80v-pk across 50-ohms.
>
> cheers, Peter
>
>
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