Troubleshoot Phillips 483x at converter stage (ech4 tube) (Techniek Radio/TV)

door ruudtx , 19.06.2018, 19:29 (2130 dagen geleden) @ Sieme

The HF stage is oscillating on 452 (IF freq). That is my guess. This explains the flat 452 signal and the RF signal block. There is a shortage or feedback in the Heptode anode circuit to the control grid. The 452 output filter sets the frequency.
Also a cap may fail that shorts the 452 signal.