[Amps] 4CX5000A in common grid circuit

[Markku Oksanen]

Hi

Peter Chadwick kindly scanned the Pappenfus pages that I needed to make my math work.Now I am trying to extract the needed parameters from the characteristic curves to see what happens.
However, it looks like that a well made GG 4CX5000A will provide some 12-14 dB gain with the high (7200V) plate volts I have available.So, there is little need to go directly to grid driven without testing the GG first. And this way, the project remains interesting.
Thank you both for your kind help.
MarkkuWW1C
> Date: Mon, 6 May 2013 19:00:46 -0600
> From: jtml at losalamos.com
> To: ww1c at outlook.com; contesting.com amps at contesting.com
> Subject: Re: [Amps] FW:  4CX5000A in common grid  circuit
> 
> 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 at outlook.com
> Date: Sat,  4 May 2013 23:05:46 -0600
> To: "jtml at losalamos.com" jtml at 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 at losalamos.com
> > > To: amps at 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...
> > > _______________________________________________
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> 
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