Screwed up!

[dwhutchens]

Any body else make this stupid mistake? I have an old power transformer from a phonograph and a Weber Princton OT wired up with a 5e3 style PI and cathode biased. It worked at first power up but when I went to check the voltages on the 6v6 tubes I found I had 300+ volts on pin 5. I discovered that I had wired pins 4 and 5 backwards I played it like that for 20 or 30 minutes. Is that hard on the tubes? Did I do any damage?

When I get that rewired how do I determine the proper value of cathode resistor? I have about 327v on the plates. I'm using a 250 ohm for the moment.

Thanks,
David

[lowell]

I don't think you did any damage. I'm not sure though. I see it as if you used the "screens" as if they were the grid. With the grid (screen) still biased relatively negative to the cathode and b/t the cathode and plate it would seem this would not cause any harm... however not sure what happens in there electronically speaking. I'm curious, how did it sound???

For biasing those tubes use ohm's law:

Max PWD for 6v6 is around 14watts. 14/327=43ma. That is your maximum!! I think you could get away w/ as low as 125ohms for a cathode resistor, but it'd be best to try one around 200ohms and go down from there while monitoring the current. Be sure it is rated for at least 15watts.

[dwhutchens]

Turns out I wasn't as stupid as I was confused. I was counting the pins counter clockwise. I guess I thought I was counting ic pins. I've got to quit working on these things late at night before I fry myself