Hi Tom, Well, you have a certainly started a string here. A couple of suggestions for you. Use the 4CX350FJ. May as well start with the lowest distortion. Don't try to employ RF feedback across more than two stages. Use one of the old TRW - Motorola - M/ACom class A bricks for the first stage. Since you are operating narrowband, consider the feed forward configuration. If you start with a -50dB distortion amp, you should be able to slice another 30dB off that figure for a -80dB system. I doubt if your exciter, at any level, is clean enough to drive the above FF system. Fortunately, a clean 80M SSB generator is easy to construct compared to the balance of this undertaking. 73 & Good afternoon, Marv WC6W -- "Tom Cathey" wrote: Thanks for the replies. Let's address a few comments. I'm trying to get the right direction to follow, then do some serious, focused study in the right areas. One comment: Why bother to get better linearity? I think for most bands, the standard GG open loop 3-500Z type amplifier is FB. You can hide in the 40M BC crap, the 20M loud crowd, 160M noise, etc. But, notice my intended amp is a 75M mono-bander. The 75M DX window is a unique situation where extremely clean signals are required often - due to the low noise floor at grayline or late afternoon when weak DX signals begin coming in S3, etc. The window is maybe 15kc wide. [3785-3800] If a local is S9+50 over, even if he is 50db down 5kc away, that is still going to cover an S3 DX station. And, if the quality is worse, the window gets pretty tough to use. So, I am looking for ways to improve upon a few exisiting GG 3-500Z's, an 8877, 160-10M amplifiers as well as build up a new, dedicated 75M monobander that can give IMD numbers higher than what is achieved with open loop GG amps, etc to address this unique 75M window problem. Let's see if we can sort out some NFB techniques here.... I don't want to pit one guy against the other, so I will not mention names from private emails or archives, just opinions... so we can discuss things without egos getting involved. Richard, you mentioned here to try 100 ohms in the cathode of my GG amp. I believe it would put the amp into cutoff, since only 10 ohms drops the idle by 1/2. It was suggested it would require a choke across this resistor to idle the amp and eliminate the DC drop and bias variation during ssb eaks - and keep the RF feedback working. There is talk in the archives of using this choke, while others strongly disagree in it's use. Here's an email I recieved from an RF engineer addressing the subject of using a cathode resistor in a GG amplifier. He is addressing my question the other day of using this cathode resistor for GG amps. [printed with his permission, but I opted to leave the name out - unless he comes into the discussion himself] " His logic is WRONG! Adding a CATHODE RESISTOR to a GROUNDED GRID (Cathode Driven ) amp does NOT increase negative feedback! The drive and the output are IN PHASE. His logic applies to GRID-DRIVEN amps, where the CATHODE and SCREEN are at/very near R.F. ground. (Usually TETRODE or PENTODE amps)-With an amp such as he described,(Grounded-Grid) he will need to add resistance IN SERIES with the R.F. Drive, NOT the cathode ground return." So there you are. Another NFB technique - Some, as above, have suggested to put a resistor in the grid circuit. I see mention of it in the archives - BUT, some say it will destabilize things - an old Orr mistake. I would like to try that technique too and will add one in series with the driver coupling cap as suggested in a private email. I'll publish results.. These two techniques sound like a great way for the average guy to slightly improve the linearity of his GG linear. So it's worth talking further about them. For my 75M mono-bander, I may go the Harris design route. I am leaning towards building something like a 6CL6 driving a 4CX-350, driving another 4CX-350, driving a 4CX-3000 with heavy feedback back to the 6CL6. 100mW in and 1500+ QRO out as clean as I can make it. We'll see. BTW, [Tnx for the correction of using"m" mW instead of "M', MW, mega vs: milli... :-) 73, Tom, K1JJ _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ___________________________________________________________________ Try Juno Platinum for Free! Then, only $9.95/month! Unlimited Internet Access with 250MB of Email Storage. Visit http://www.juno.com/value to sign up today!