Where do you bias your EL34 Uberschall?

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TheMagicEight

TheMagicEight

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The EL34 Uber is considered 120w, right? Would that mean for the bias equation you'd want to do 30w divided by plate voltage?

My plate voltage is about 550v, which makes 70% at 38mA. That seems high to me, especially considering Bogner recommends keeping bias under 30mA. I'm thinking Bogner might recommend a lower value for reliability reasons, but I don't know. Where are you running yours?
 
TheMagicEight":14xwseeg said:
The EL34 Uber is considered 120w, right? Would that mean for the bias equation you'd want to do 30w divided by plate voltage?

My plate voltage is about 550v, which makes 70% at 38mA. That seems high to me, especially considering Bogner recommends keeping bias under 30mA. I'm thinking Bogner might recommend a lower value for reliability reasons, but I don't know. Where are you running yours?
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They do recommend them low. Usually what I do is find the 70% and 80% ratings for the PV. Then, go ahead and turn the gain midway and the master up just a little bit and listen for the amp to start making some hiss. Whatever this value is and as long as it is in a safe range, is where I leave mine. Keep in mind though, that most 34's are rated for 600V. Take one like the Uber that pumps out 550V (that seems a little high) and you are stressing the hell out of the tubes anyway. This is one reason I like the Winged C's and JJ 34L's as they are rated higher. Ruby's BHT is the same.

Have you checked your wall voltage? If your input voltage is high, it will affect the output DC voltage a lot. My voltage over here runs anywhere from 120V-128V and the Hz is all over the map. For a 117VAC input trannie, if the wall voltage is high at 128V, this 11VAC will affect output DCV by about 2-3:1, depending on the transformer. When I was supposed to be get 490V in an amp, I was seeing around 520PV and couldn't keep tubes in a couple of amps. So, I got the biggest and baddest ass Voltage Regulator/Stabilizer I could fine. Now, I got nice, clean 110V to my amps. Just something to consider.

Steve
 
Thanks guys! I just checked the voltage here. My meter says about 124VAC, so I guess a voltage regulator will be one of my next purchases.

I rebiased the Uber at 31mA and it sounds much better! When I first converted the Twin Jet to EL34s I didn't have the right resistor, so the bias would only go so low. I switched it out for a better value and now it's even more alive than before!
 
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