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## Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback

 To: , Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback "Tom Cathey" Tue, 27 Dec 2005 16:10:06 -0500
 ```Hi Bob, Thanks for the suggestion. You make a good point of possibly eliminating the 6146 pre driver. I thought about that myself, but didn't have enough knowledge to know if I would have enough gain left to reduce the overall gain with 20 db of negative feedback afterwards. Figured I'd just try it and see. Well, I know that the 4CX-XXXX final [they're all similar] will need about 300 volts of swing. And the OPA-695 will do 10db gain. That's 5mW to 50mW. I figured I'd put two OPA-695's in cascade for 20db = 500mW. Into 50 ohms, 500mW = 5V. So we have 5V to drive the 4CX-250 driver. And, the 9:1 transformer will make it X3 = 15V, right? This is a 9:1 impedance ratio = 3:1 voltage ratio...? Anyway, with 20 db of negative feedback from the final to the 4CX-250 driver will mean a 20db reduction in gain. I suppose a lot depends upon the gain of the 4CX-250 driver and the transformer. This is where I am not sure how to calculate it and proceed. [20 Log db for voltage, etc.] ie, Will an OPA-695 putting out 500mw into an X? step up ratio transformer that drives a 4CX-250, that drives 300v into a 4CX-XXX X final with 20db of negative feedback have enough system gain? And, will the 9:1 voltage step up transformer have absolutely no affect on the low distortion goal... even if a small space charge current is pulled? What if we need more than 9:1 step up, can it be done with cascaded transformers without ill effects? BTW, I'm curious why you feel the transformer will have bandwidth limitations... are we talking of a broadband unun torroidal type? Opinions? 73, Tom, K1JJ > Before you close the case Tom something else for you to consider. To drive > a GG Amp you place watts on the cathode. To drive a Grounded Cathode Amp > you place volts on the grid. This provides you with a cheap and easy way > to increase the gain of any stage. Simply insert a voltage transformer in > the input. With a 1 to 9 unit on the input of the 4CX250 stage you should > be able to chop out the 6146 and drive it directly with the OPA-695. The > draw back of this method is the available operating bandwidth. Seeing as > you intend to use this in a monoband application this should not pose a > problem. The other thing to consider is the distortion generated by > saturating the transformer core. Hardly a problem worth considering at > that power level. _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
 Current Thread Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, (continued) Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, Bill L. Fuqua Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, wc6w@juno.com Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, wc6w@juno.com Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, w6ah Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, Tom Cathey <= Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback, wc6w@juno.com