02-18-2014, 11:28 PM
I have at least two working (I have Leader LSG-11 for some time and recently got SG-8 Heathkit in Kutztown for 5 bucks). I have some more but did not get to them yet.
Now my main qualm with them is the waveform while perfectly sinewave at the input of the cathode follower (the schematics are fairly similar to the point of being the same between the two) comes out distorted from the follower's output. Usually the bottom is somewhat clipped. The load is the same in both cases - 1K resistor in series wirth 1K pot.
The chart in SG-8 suggests -2 to -15V at the grid of the follower depending on the frequency but I measure pretty much 0V. The only thing that could offset DC bias is the load itself.
Anyway, I was trying to make the Heath work as it refused to work at most of D (6 to 24MHz) and all of E (26 to 110 MHz) bands.
The tubes in the oscillators are 12AU7 in Heath and 12BH7 in Leader. The tubes are very similar (though not totally identical). I had a spare 12BH7, so I yanked out 12AU7 and replaced it with 12BH7. After that the SG-8 works on all bands. And in some of them the output is fairly sinusoidal in shape (well, it now behaves similar to the Leader).
Of course it is not calibrated - the frequency is roughly about what numbers tell, but if in Leader with exception of the C band they are right on the money (checked with the counter I have) in Heath they are good few percent off (higher).
I'm OK with it, I even check Leader with counter first before using it for alignment, so as long as I do that the only thing that matters is the oscillation itself being present.
Well....now I have two oscillators, and I have another SG-8 and then I have a larger something, forgot what, that Sam (Mafiamen) gave me. Will fix them and see which one I like best.
PS. Oh, and I replaced tacky sticky grimy power cord.....now I do not feel like "yack!!!" when I have to plug it.
So much for today's evening (other than performing the second re-aligning of the 70).
G'nite!!!
Now my main qualm with them is the waveform while perfectly sinewave at the input of the cathode follower (the schematics are fairly similar to the point of being the same between the two) comes out distorted from the follower's output. Usually the bottom is somewhat clipped. The load is the same in both cases - 1K resistor in series wirth 1K pot.
The chart in SG-8 suggests -2 to -15V at the grid of the follower depending on the frequency but I measure pretty much 0V. The only thing that could offset DC bias is the load itself.
Anyway, I was trying to make the Heath work as it refused to work at most of D (6 to 24MHz) and all of E (26 to 110 MHz) bands.
The tubes in the oscillators are 12AU7 in Heath and 12BH7 in Leader. The tubes are very similar (though not totally identical). I had a spare 12BH7, so I yanked out 12AU7 and replaced it with 12BH7. After that the SG-8 works on all bands. And in some of them the output is fairly sinusoidal in shape (well, it now behaves similar to the Leader).
Of course it is not calibrated - the frequency is roughly about what numbers tell, but if in Leader with exception of the C band they are right on the money (checked with the counter I have) in Heath they are good few percent off (higher).
I'm OK with it, I even check Leader with counter first before using it for alignment, so as long as I do that the only thing that matters is the oscillation itself being present.
Well....now I have two oscillators, and I have another SG-8 and then I have a larger something, forgot what, that Sam (Mafiamen) gave me. Will fix them and see which one I like best.
PS. Oh, and I replaced tacky sticky grimy power cord.....now I do not feel like "yack!!!" when I have to plug it.
So much for today's evening (other than performing the second re-aligning of the 70).
G'nite!!!
