01-07-2012, 08:53 AM
Hello Alan, it's a Radiotron 6SA7 (octal) the only spare bases I have are octal also, I will probably get off my bum and scout a couple of car boot sales for some scrappers for spares at some point.
Just to restate the 6SA7 is working ok and the valve is up to spec according to my Hickok valve tester, the biggest challenge with this project is producing the higher order harmonics of sufficient amplitude to drive the mixer and selecting the required harmonic while rejecting the adjacents down to a reasonable level, obviously Q plumits the further up the shortwave spectrum we go, still it's the amplitude that is the most important at the moment, I have had the receiver working on 27 to 28 megs by extracting the 30th harmonic for the mixer osc feed but it is weak at those frequencies.
At some point I will arrive at the best that is obtainable within the given design brief.
Lawrence.
Just to restate the 6SA7 is working ok and the valve is up to spec according to my Hickok valve tester, the biggest challenge with this project is producing the higher order harmonics of sufficient amplitude to drive the mixer and selecting the required harmonic while rejecting the adjacents down to a reasonable level, obviously Q plumits the further up the shortwave spectrum we go, still it's the amplitude that is the most important at the moment, I have had the receiver working on 27 to 28 megs by extracting the 30th harmonic for the mixer osc feed but it is weak at those frequencies.
At some point I will arrive at the best that is obtainable within the given design brief.
Lawrence.
