For the #102 circuit, the layout indicates that the bias was set at 30.3mA @ 465.5 VDC on the plates. This equates to about 14 watts static dissipation per tube. Does anybody know where this info came from and if so what was the line voltage when this reading was taken?
My reason for asking is that my #102 build sounds really raspy biased that low and doesn't really start smoothing out till I get it up to 15 or 16 watts. I know that Robben's tech indicated that he ran his Dumble on a Variac set for about 125 volts. I was wondering if perhaps the overall bias wattage on his amp was perhaps higher than the schematic indicates due to different line voltage when the reading was taken.
-Aaron
#102 Bias Setting
Moderators: pompeiisneaks, Colossal
Re: #102 Bias Setting
Aaron, I believe that info actually came from Brandon when he was inside that amp. IMHO, you are overanalyzing your build; since you don't have the actual #102 or the ability to A/B them side by side, any discrete info regarding the actual 102 amp is only relative to itself. If your amp to you sounds better at 15 or 16 watts, then give it what it wants and enjoy it.aflynt wrote:For the #102 circuit, the layout indicates that the bias was set at 30.3mA @ 465.5 VDC on the plates. This equates to about 14 watts static dissipation per tube. Does anybody know where this info came from and if so what was the line voltage when this reading was taken?
My reason for asking is that my #102 build sounds really raspy biased that low and doesn't really start smoothing out till I get it up to 15 or 16 watts. I know that Robben's tech indicated that he ran his Dumble on a Variac set for about 125 volts. I was wondering if perhaps the overall bias wattage on his amp was perhaps higher than the schematic indicates due to different line voltage when the reading was taken.
-Aaron
TM
Re: #102 Bias Setting
Thanks for the info! You're probably right. My build does differ in many respects from the real thing to begin with. I guess a lot of my second guessing comes from reading so many other people's recommendations for colder bias settings on these amps too. I'm just wondering if there's something strange about my build or my ears or something.ToneMerc wrote: Aaron, I believe that info actually came from Brandon when he was inside that amp. IMHO, you are overanalyzing your build; since you don't have the actual #102 or the ability to A/B them side by side, any discrete info regarding the actual 102 amp is only relative to itself. If your amp to you sounds better at 15 or 16 watts, then give it what it wants and enjoy it.
TM
I also have read the '60% of max' recommendation in a few different places, but am not sure if they mean 60% of 23 watts, 30 watts, 25 watts or what. The end results are wildly different depending on what you consider "max" for a 6L6. I guess I should probably just use my ears and not sweat it unless they're red-plating or melting.
-Aaron
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martin manning
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Re: #102 Bias Setting
Do I remember correctly that you are running SED 6L6's? They are widely reported to sound better at higher idle bias settings as compared to other 6L6 types. If you are measuring cathode current via 1R cathode resistor and getting ~15W you are below 50% Pa if you correct for screen current. That makes it pretty cold for any 6L6, and what you are hearing is probably crossover distortion. At 465V, being conservative by ignoring the screen current, 70% Pa (21W) would require 45mA cathode current. I see nothing wrong with finding a spot that sounds good to you, as long as its at or below 45mA.
Re: #102 Bias Setting
Thanks for the reply! I'm running a set of Winged =C= 6L6s in there. I get about 450V on the plates with 120VAC line. I've have been using the cathode resistor measurement method, but completely neglected to compensate for screen current.martin manning wrote:Do I remember correctly that you are running SED 6L6's? They are widely reported to sound better at higher idle bias settings as compared to other 6L6 types. If you are measuring cathode current via 1R cathode resistor and getting ~15W you are below 50% Pa if you correct for screen current. That makes it pretty cold for any 6L6, and what you are hearing is probably crossover distortion. At 465V, being conservative by ignoring the screen current, 70% Pa (21W) would require 45mA cathode current. I see nothing wrong with finding a spot that sounds good to you, as long as its at or below 45mA.
-Aaron
Re: #102 Bias Setting
Just to be clear, SED and Winged C are the same thing.
Re: #102 Bias Setting
That's right. I can't keep 'em straight anymore. In my head I still think "Svetlana."sharkboy wrote:Just to be clear, SED and Winged C are the same thing.
-Aaron