[AMPS] drive xmfr ratios

[nospam4me@juno.com]

:From: "Maurizio Panicara" <i4jmy@iol.it>
:Once I've seen a grid driven amplifier in which a ferrite broadband
:transformer 50/200 ohm was used, probably to develop a bigger 
:voltage across grid without increasing the driving power. The 200 
:ohm port, that one going to the grid, was also terminated in a 
:200 ohm non inductive resistor but its size wasn't sure good to 
:dissipate large power and was probably there to establish a load 
:impedance, and nothing else. 

My 4cx250 amplifier uses a 9:1 ratio (50/450) terminated into two 
parallel 1.5K resistors and the LC networks. No problems with 
stability and my 10 watt max exciter drives it to full input. 
Last number crunch gave >17dB gain. You can have a look at the 
partial circuit at http://sonic.ucdavis.edu  Amateur Radio Pages. 

I would shy away from this higher ratio when the size of the tube 
requires handles. The stability requirements become more 
important. Though I've never had any problems using 9:1, I use 
it only because of the limited drive from my 10 watt exciter.

cheers
skipp 

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