I've got a big back porch area that I've closed in with temporary materials but with a space heater I will be able to keep on working on it through out the winter months.
Yesterday I attempted aligning the chassis which I have aligned once before. But I couldn't help but put my tweaking fingers on it until it was out of alignment...so I was aligning it for the 2nd time when I come to the step for the shortwave trimmer. When I put 18MC on it I had nothing but motorboating. I deduced that it was a bad tube because it was sensitive on the 1st alignment and motorboating on the 2nd alignment. I put the 6A8 tube on my tube checker and it showed bad grid leakage. This is the first time I've found a bad tube on my checker. It was hard to find but I've got one coming. Does the 6A8 tube seem to be appropriate to fix this condition...Neal
Best Regards,
Bill Grimm
As far as I recall, it is more difficult for oscillators to function at higher frequencies, and so excessive leakage might pull down oscillation. Control grid circuits are usually very sensitive high impedance circuits (especially when fed with capacitors, as is often the case), and so any leakage would drastically affect performance. Internal leakage might also cause unwanted feedback, depending on what the grid was leaking to. If you are getting leakage, you might also have a gassy tube. Gassy tubes will cause at least one half of the neon shorts light to glow on my EICO 625 (which would indicate leakage). Ionized gas will allow electrons to flow in any direction, and not just from the cathode to the other elements, and this will allow all sorts of havvoc to take place within the tube, especially on the high impedance grid circuit.
T.