The 520 was my first rig as a novice. I really enjoyed every moment of it. I later upgraded to a TS-140. Then ended up selling the 520. Hated doing that. Many years later a friend of mine fell ill and wanted to sell off his station. So I ended up buying his 520 and Electra voice 638 mic. The rig looked ok but it would not perform well.
You could not tune anyone in and make it undestandable. Was just a warble.
After tearing it down I found the grease in the VFO had become dry and hard. This was causing the rotor in the VFO to not make contact. Had to wash all that old grease out, replace with fresh and it now worked for the past 12 years.
You will enjoy that rig.
Keep your bias set correctly. If you take it apart again and have an ESR meter check the mains filter caps and any cap in the RF stage. There is a lot of heat in that circuit and a caps ESR can rise. This will cause tuning issues and shorten the life of your tubes. Also when you are inthere look at the screen and bias resistors. See if they show any signs of over heat.
If you have to replace mains filter caps I use Rubycon 180uf @ 450VDC. These caps measure 1 3/8 inch diameter x 1 inch tall. And remember any replacement cap you choose the top is exsposed and have voltage there. Simple fix is to remove the end from your original cap and hot glue them to the new cap.
