jtcnj
Ambassador of the Crossroad
No, my PT didnt sh*t the bed yet.
But, it sounded a bit off and the volume seemed a bit lower than I recall. That didnt get me inside the chassis.
I was in there to ID the PT leads, and check and bias it a bit hotter. It has the stock sovtek 5881/6L6 somthings, anyway they are considered a 26w tube. the pair is only 5ma mis matched but thats around a 10% mismatch in plate dissipation, which was at 65/55%. I eventually upped it to 75/65% and will probably go to get the lower up around or above 70%, but I will let the ears decide.
So, I got no voltage drop across v8 OT winding and the tube was barely warm. Took a little swapping, head scratching, hand wringing, - throw in a few "woe is me" as well. (Just had a similar problem with the 5E3 build what turned out to be a failed socket terminal)
I spy the 2 screen resistors, and right away recognize the 470Ω color bands on v7. v8 looks like black black brown = 00 x 1? Ruh roh. Well it went over current, got hot and turned color, like they always do.
It failed open, then broke in half when I grabbed it with needle nose.
I replaced it, biased the tubes and kept shooting the tubes and screen resistors with a temp gun. Stayed all good.
I put in the ebay Soviet military surplus 6L6 equivalents I tried recently - just to make sure they work- thought they were the culprits. Stable.
I dont know what caused it but am going to pull the chassis again and play it like I stole it and keep watch on those resistors!!
I meant to take pics but it was 95+°F in the garage and I was pretty cranky to boot.
But, it sounded a bit off and the volume seemed a bit lower than I recall. That didnt get me inside the chassis.
I was in there to ID the PT leads, and check and bias it a bit hotter. It has the stock sovtek 5881/6L6 somthings, anyway they are considered a 26w tube. the pair is only 5ma mis matched but thats around a 10% mismatch in plate dissipation, which was at 65/55%. I eventually upped it to 75/65% and will probably go to get the lower up around or above 70%, but I will let the ears decide.
So, I got no voltage drop across v8 OT winding and the tube was barely warm. Took a little swapping, head scratching, hand wringing, - throw in a few "woe is me" as well. (Just had a similar problem with the 5E3 build what turned out to be a failed socket terminal)
I spy the 2 screen resistors, and right away recognize the 470Ω color bands on v7. v8 looks like black black brown = 00 x 1? Ruh roh. Well it went over current, got hot and turned color, like they always do.
It failed open, then broke in half when I grabbed it with needle nose.
I replaced it, biased the tubes and kept shooting the tubes and screen resistors with a temp gun. Stayed all good.
I put in the ebay Soviet military surplus 6L6 equivalents I tried recently - just to make sure they work- thought they were the culprits. Stable.
I dont know what caused it but am going to pull the chassis again and play it like I stole it and keep watch on those resistors!!
I meant to take pics but it was 95+°F in the garage and I was pretty cranky to boot.
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