Hi
I am back from the underground. Much of my experience has been at VHF, 100-200
Mhz range. However, same applies for HF, except neutralization and circuits are
different. Tetrodes work well in grounded grid or grounded cathode, as long as
the DC ratings are cared for and the grids have proper bias.
I am presently using two tetrodes in grounded grid cavity circuits as linear
amplifiers. These are modern ceramic metal tetrodes, larger than hams would
use. They both have gains of 25-30 depending on voltages and tuning. That's 14
to 14.7 dB of power gain. Screen grid has full DC as does control grid, with RF
bypasses to ground (in cavity circuits).
In the 1980s at Broadcast Electronics, I ran the 4CX3500A tetrode from Eimac in
2 circuits, a grounded cathode and a grounded (common) grid. The output cavity
was same for each, only different socket deck. The tube is an offshoot of the
4CX5000A design, shorter with lower inductances and better VHF characteristics.
With 5200 volts on the anode and some screen voltage (memory fails me), the
gain in grounded grid (for RF) was 17.8 (12.5 dB) and in grounded cathode (grid
driven) was 37 (15.7 dB). We chose the latter for our transmitter at 3 - 6 kW
power rating.
73
John
K5PRO
-----Original message-----
From: Markku Oksanen ww1c@outlook.com
Date: Sat, 4 May 2013 23:05:46 -0600
To: "jtml@losalamos.com" jtml@losalamos.com
Subject: FW: [Amps] 4CX5000A in common grid circuit
>
>
>
>
>
> All
>
> I found this
> http://www.cpii.com/docs/related/22/C&F4Web.pdfand it looks like chapter 4 >
> of Pappenfus' if I understand it correctly.
> Against current "wisdom" this states (page 104) that a properly designed t>
> etrode in GG will give a gain of 20 to 50 while triodes tend to remain belo>
> w, at the level of 7 to 20, 20 seems to be a sign of a good design thes> e
> days with modern high muu tubes.
> Can anybody help with this??? Is this correct? I have never before heard >
> that tetrodes in GG can give such high gain. Are there specific requirement>
> s for the tube??
> I still didn't find direct gain formula but managed to calculate some estim>
> ates based on voltage gain and impedance levels. What the GG muu value to >
> use with a tetrode is, I don't quite know.
> Looks like it makes good sense to try a GG design first with the some foret>
> hought in case grid drive becomes a necessary change later. Gain of over 20>
> is plenty good enough.
> Thanks for the hint / help!
>
>
> Markku WW1C
>
> > Date: Thu, 2 May 2013 16:28:16 -0600
> > From: jtml@losalamos.com
> > To: amps@contesting.com
> > Subject: [Amps] 4CX5000A in common grid circuit
> >
> > 4CX5000A is in the Collins design in the 1964 Ed of Pappenfus' SSB Princi>
> > ples. It will give you a reference point. If you can find the NAB handbook
> > > from the 1986 era, I wrote the section in FM transmitters, comparing a >
> > 4Cx3500A in to and gg circuits, class c though, at 100 MHz. Its a simil> ar
> > but better tetrode. If you put voltage on the screen you can get fairly >
> > high gain, like 12 db I think. Memory may be fading here.
> >
> > Sent from on the road...
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
> >
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