Hi All, I'm planning to build up a 75M monoband amplifier that has at least -45db to -50db 3rd order IMD using heavy RF negative feedback. 10MW in, 1500W out. I wanted to get opinions here what other
Tom, Sounds smart. Forexample the old Collins 204C-1 amplifier first has a 4CX250B in Class A that drives a 4CX250B in clas AB1 that drives a 4CX5000 in AB1, I bet that thing would show pritty good n
2 cent reply de k5gw: You will need a reliable test setup to know when you have reached your design goals. You might consider starting with the test setup and do a thorough evaluation of your FT1000D
Tom, Gates had a commercial amplifier (MODEL ST-3A) with 2nd harmonics down 50 db and all higher order down at least 60 db. The input was 100 mw and the tube line up was: a 6CL6 in class A, an 8122 i
Or, upgrade to the 9000 that puts out 75 Watts class A. :) 73, Keith NM5G 2 cent reply de k5gw: You will need a reliable test setup to know when you have reached your design goals. You might consider
The 3cx3000A7 already exceeds 50db total IMD without RF-NFB. In class A, a 4cx10,000D / 8171 will equal that, and if you need 10db more suds, there's no pain, just turn up the mic gain. Richard L. Me
Thanks for all the replies! cheezz... I got close to 15 private ones and they're still coming in - really appreciate the ideas, guys. Please excuse me if I don't answer them all... K5GZ [good whiskey
Tom, if you are operating AM as in steady carrier, the resistor bias is probably ok. If you plan to operate SSB or cw then the bias voltage will be changing from zero with no drive to a maximum value
Yes, Gerald, I thought about the DC bias variation too... the fact it would be swinging under ssb modulation... and thought that was not a good thing unless the tube was run in class A. This is class
Correction: It was pointed out to me that the cathode resistor for negative feedback is to be used only for a grid driven [grounded cathode] amplifier to generate degenerative [negative] feedback. In
Seams like a BIG load to me. 10 Mega Watts in and only 1500 Watts out ? 73 de SM3PXO Hi All, I'm planning to build up a 75M monoband amplifier that has at least -45db to -50db 3rd order IMD using hea
Doesn't grounded grid/cathode driven operation provide much if not all of the degeneration/negative feedback we are discussing here? 73, K5GW In a message dated 12/14/2005 11:10:17 P.M. Central Stand
A 3-500Z will do c. 45db total IMD without a cathode feedback R. Adding one will reduce distortion - with the tradeoff of higher drive requirement. Richard L. Measures, AG6K, 805.386.3734. www.somis.
Hi Tom, Put the resistor in series with the input coupling capacitor. If you want to experiment with negative feedback with multiple GG drivers you might try link coupling between stages. You can rev
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This is a question I've often wondered about. Does a cathode resistor in a grid-driven amp actually produce negative feedback, or does it merely redu
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 li
An unbypassed cathode resistor in a grid driven amp does in fact provide negative feedback. It is often done in audio amplifiers to improve distortion. As the grid is driven positive the plate voltag
I like BOTH suggestions, Gary! Having the input link phase reversable opens the door for GG driving GG experiments. For the GG input drive NFB resistor, what value would you try for an 8877 input? It
As a CW operator, I don't have to contend with wide SSB signals. But a big problem with strong local signals, both CW and SSB, is phase noise generated in the low level exciter stages. I suggest that
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