Moderators: pompeiisneaks, Colossal
running into 4k, it was louder, more headroom, a bit less distortion(more defined)...wider bandwidth. The 8k load was compressed and darker by comparison, less power.Firestorm wrote:Yeah, that sounds the opposite of what you'd expect. But the tube data all seems to take the design maximum ratings pretty seriously and don't say what happens much above 300V. Running into the 4K, did the output seem to have more distortion? I think Fender ran the BF Deluxe Reverb into 6,600 -- maybe a compromise between power and distiortion.
Thanks David!! I definitely got frustrated looking at the available curves...didnt think to do what you did.David Root wrote:If you take the 6V6 plate curve and extrapolate by marking the 285V g2 line above the 250V g2 line (I superimposed the 285V points from a Radiotron 6V6 curve on a Tungsol 250V curve, both out of tubedata.org), then extrapolating first 300V g2 then 350, then 400, above those lines, the 400V g2 knee is about 215 mA and the knee voltage about 110.
Now I realize that this is pretty crazy stuff but bear with me.
So Za= (415-110)/0.215= about 1420 ohms. X 4 for a pair = 5,680 ohms Zaa. Depending on your bias point you might be running very hot. Putting 8k ohms in instead of 5k7 reduces power output dramaticallyand no doubt gross distortion too, so it also makes sense to me that Fender might well have picked 6k6 as a compromise.
If it sounds great at 8k AND your dissipation is under control, go for it!
Makes sense.Wow. You have too much time on your hands. But that WAS a great analysis!David Root wrote:If you take the 6V6 plate curve and extrapolate by marking the 285V g2 line above the 250V g2 line (I superimposed the 285V points from a Radiotron 6V6 curve on a Tungsol 250V curve, both out of tubedata.org), then extrapolating first 300V g2 then 350, then 400, above those lines, the 400V g2 knee is about 215 mA and the knee voltage about 110.
Now I realize that this is pretty crazy stuff but bear with me.
So Za= (415-110)/0.215= about 1420 ohms. X 4 for a pair = 5,680 ohms Zaa. Depending on your bias point you might be running very hot. Putting 8k ohms in instead of 5k7 reduces power output dramaticallyand no doubt gross distortion too, so it also makes sense to me that Fender might well have picked 6k6 as a compromise.
If it sounds great at 8k AND your dissipation is under control, go for it!
Very interesting! I recently converted my Rivera Thirty Twelve to 6V6's and found essentially the same voltage scenario (420v plate). I installed a Boogie Rectoverb OT which measured 4K@8 ohms and used the 4 ohm tap for my 8 ohm speaker---voila 8K P-P load. Bias is about 55 mA for the pair. It sounds ok, but not as chimey as DR or even my old Princeton Reverb.David Root wrote: So Za= (415-110)/0.215= about 1420 ohms. X 4 for a pair = 5,680 ohms Zaa. Depending on your bias point you might be running very hot. Putting 8k ohms in instead of 5k7 reduces power output dramaticallyand no doubt gross distortion too, so it also makes sense to me that Fender might well have picked 6k6 as a compromise.
If it sounds great at 8k AND your dissipation is under control, go for it!
Do you know where you heard that? I'd love to understand the logic behind it. Even if it sounds way over my headexmaxima1 wrote:BTW, I always heard that using an OT with lower impedance will increase the even-order distortion, making the sound more full. Maybe that's the reason the 4K load sounded so good to the original poster of this thread.
Hey, can you do me a favor and try the 8ohm tap first and report what you found?exmaxima1 wrote:
Very interesting! I recently converted my Rivera Thirty Twelve to 6V6's and found essentially the same voltage scenario (420v plate). I installed a Boogie Rectoverb OT which measured 4K@8 ohms and used the 4 ohm tap for my 8 ohm speaker---voila 8K P-P load. Bias is about 55 mA for the pair. It sounds ok, but not as chimey as DR or even my old Princeton Reverb.
I have a spare Trace Elliot Velocette OT that measures 6K P-P at 8 ohms. I will try that.
BTW, I always heard that using an OT with lower impedance will increase the even-order distortion, making the sound more full. Maybe that's the reason the 4K load sounded so good to the original poster of this thread.
