EL34 not glowing blue

[Dave1992]

Hey guys,

So last night while jamming with the band, I've notice my Marshall's (1959slp w/PPIMV) volume started fluctuating. It kept its usual volume and dropping down/going up to its regular volume.

The last time it happened the power tubes were going bad, but I've noticed that on V4 and V5 that the tubes weren't glowing blue. I've swapped them for V6 and V7 and it didn't follow the tubes.

Could it be that the screen grid resistors died as well? The power tubes are about 4 years old now.

EDIT: All of the screengrids test at 1k ohm on my DMM
Thanks!

[Dave1992]

Ok... So my previous tech installed a 1,5 ohm across Pin 1&8 on V4 and V7.

There is no resistance across Pin 1&8 on V4 and V5, but there is on V6 and V7. There is negative voltage and B+ across all the power tubes. At the momment, there is 70mv on V6/V7 and nothing on V4/V5.

[Dave1992]

Anyone's got any clues to what's going on? The output jack socket seems to be grounded on the Tip and the Sleeve as well.

There aren't any blown component anywhere and what needs to show continuity is there aswell.

Can I just put some fresh tubes, bias it and play??

[Dave1992]

So for everyone reading this thread... I've replaced the 1,5 ohm resistor that died and everything seems fine so far. The bias took some that to reajust around 43,5-45,5 ma. Sounds good so far.