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Hi Everyone,
Background: Weber kit build, incorrectly spec'ed PT 375-0-375, plate voltages were 430+ which caused it to be biased very hot. I played around with the bias resistor and found that ~870ohm 5w did the trick.
Fast forward 2 years... So, here we are. I often though of getting the correct PT for my 5f1 and finally did the swap this past weekend. I have a Heyboer 330-0-330 in there now with better plate voltage readings. However, I've got some questions on bias. Here are my readings:
-=V2=-
P3 = 377v
P8 = 22v
With the 'stock' 470ohm resistor I get 46mA of plate current (22/470). This is a bit hot -- gives 16.52watt plate dissipation. Side note, ran these figures through the weber bias calculator and it gave 8 watts... Not sure what I'm doing wrong. The first question is, is my bias calculation correct?
Next: I had a NOS brimar 6v6g in while I was doing the work and ended up killing it for some reason. After the PT swap, it gave up the ghost while I was playing -- just a gradual loss of volume, then nothing. I didn't do anymore testing, just swapped in a Tesla/JJ 6v6 and kept going. This also gave some strange noises while I attribute to rattle (almost every 8 note sounded terrible). Then, put a crappy Chinese 6v6 -- all is good. One note: while I was doing the PT swap I didn't have things properly grounded after the work was complete. Is it possible that the tube was ruined this way?
Background: Weber kit build, incorrectly spec'ed PT 375-0-375, plate voltages were 430+ which caused it to be biased very hot. I played around with the bias resistor and found that ~870ohm 5w did the trick.
Fast forward 2 years... So, here we are. I often though of getting the correct PT for my 5f1 and finally did the swap this past weekend. I have a Heyboer 330-0-330 in there now with better plate voltage readings. However, I've got some questions on bias. Here are my readings:
-=V2=-
P3 = 377v
P8 = 22v
With the 'stock' 470ohm resistor I get 46mA of plate current (22/470). This is a bit hot -- gives 16.52watt plate dissipation. Side note, ran these figures through the weber bias calculator and it gave 8 watts... Not sure what I'm doing wrong. The first question is, is my bias calculation correct?
Next: I had a NOS brimar 6v6g in while I was doing the work and ended up killing it for some reason. After the PT swap, it gave up the ghost while I was playing -- just a gradual loss of volume, then nothing. I didn't do anymore testing, just swapped in a Tesla/JJ 6v6 and kept going. This also gave some strange noises while I attribute to rattle (almost every 8 note sounded terrible). Then, put a crappy Chinese 6v6 -- all is good. One note: while I was doing the PT swap I didn't have things properly grounded after the work was complete. Is it possible that the tube was ruined this way?
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