02-05-2014, 09:00 AM
If the 84 has a short, most likely it will cause the resistor to smoke almost immediately, while if it takes 20 seconds or so then it indicates that the short is external to the tube.
Even there is a dead short across the B+ line, there would be no current through the resistor until the 84 warms up. Since Fibber mentioned that it only took 5 seconds for the resistor to get hot my guess is that the 84 is bad. He also mentioned that he put an ohmmeter from B+ to ground and found no short ( across filter cap 58 ).
The B+ line is the output of the rectifier and filter which supplies operating voltage to the plates and screen grids of the tubes.
Try another 84 tube and see if it cures the problem.
There is a guy on ebay selling new military surplus 84's. I would trust these more than buying a used tube.
http://www.ebay.com/itm/SYLVANIA-JAN-6Z4...1#shpCntId
Even there is a dead short across the B+ line, there would be no current through the resistor until the 84 warms up. Since Fibber mentioned that it only took 5 seconds for the resistor to get hot my guess is that the 84 is bad. He also mentioned that he put an ohmmeter from B+ to ground and found no short ( across filter cap 58 ).
The B+ line is the output of the rectifier and filter which supplies operating voltage to the plates and screen grids of the tubes.
Try another 84 tube and see if it cures the problem.
There is a guy on ebay selling new military surplus 84's. I would trust these more than buying a used tube.
http://www.ebay.com/itm/SYLVANIA-JAN-6Z4...1#shpCntId
