[Amps] Designing the Cleanest Linear with RF Negative Feedback

[w6ah@comcast.net]

-------------- Original message -------------- 
From: "Tom Cathey" <K1JJ at comcast.net> 

> Just to keep the reflector updated with info... 
> So, I am back to using a class A, grid driven, tetrode chain with negative 
> feedback as follows: The 5mw tap from the FT-1000D, into the OPA-695 op amp 
> [500 mW out], the 6146 or 6550 class A, [20V out] into the 4CX-250/ 
> conduction cooled version class A [300V out] driving a 4CX-XXXX final. 
> The final will have negative feedback back to an early stage. The 
> neutralization and feedback may be tough on the higher bands, but maybe with 
> some swamping and good layout I can pull it off. 
> 
> Case closed. 
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. 

It's nice to have this good advice and save lots of wasted 
> effort. 
> 
> Just wanted to add these notes for the archives. 
> 
> 73, and the best of holidays! 
> 
> Tom, K1JJ 
> 
> 
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