I remember telling about this at the amps reflector some time ago, but since it happened again this week, I wished to illustrate with examples (I repair tcvers., amps, etc. so from time to time an occurrence is expected). I uploaded a couple of photos of two resistors (under Photo section, "Exploded Resistors"), these were located as cathode resistors (both in parallel) in the final amp of a Kenwood TS-820S (two 6146B's in parallel, 100..120 watts out). Although the cathodes are decoupled with several 0.01 uF disk capacitors, every time this type of resistors (metal film, and also "modern carbon") are used, they explode with a loud bang at the RF peak (sustained whistle or "OOOOOOOOOOOOOOOO").
This tcvr was previously repaired (the correct values are either four 20 ohms or two 10 ohms, in parallel; 5 ohms final value) and so the 8.2, 2 watts and 10 ohms, 1 watt.
It is not a matter of dissipation, also not a matter of high voltage, but anyway they still explode if used there. The only type of resistors suitable for the cathode return is the old (brown coloured body) carbon, and some found in old AM transistor portable radios, which have the leads painted.
The link is:
Does anybody in the group had any similar experience?.
Best regards
Guillermo - LU8EYW.
