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In Reply to: RE: Power tube for Bass SET or SEP ? posted by hifipaul on February 28, 2015 at 14:49:08
I disagree with nearly everything in this post.
Back EMF should not be a go-to consideration for designing a subwoofer system, just use the impedance curve...
Zero feedback amplifiers can drive subwoofers, but driver QE needs to be adjusted accordingly.
High efficiency drivers with light cones, reasonably tight suspensions, shorting rings, etc. aren't going to give you a whole ton of back EMF.
A woofer with tons of back EMF will do gnarly things to a push-pull tube amp with a lot of global feedback (stability).
The cathode feedback winding comments are baseless.
Follow Ups:
global FB can do all sorts of gnarly stuff...the stuff you mentioned being just a small sub-set I think. I have not built anything with it in a long time, and see no reason to resume.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I agree, when you narrow your focus to increasing damping and lowering distortion at all costs, often times those costs are high!
I have a pair of 18" RCF woofers that I can drive to uncomfortable levels with 300B's. They measure reasonably well, about 3dB down around 25Hz.
Been thinking about this for a while, and the two things I want to do are boost L and drop reflected load. Three big sweeps in parallel should be able to run a 600 Ohm primary. Figure 300 mA of idle current, and E-Linear local FB to drop the source impedance and we're off...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Why not just use a single 6C33?
not enough plate dissipation. And they take more heater current that the sockets can stand reliably, and by the time you have done enough plate to grid on the big sweeps to reduce their gain to parity with a 6C33 the sweeps will have lower plate resistance( not that you need to go that far ).
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I keep hearing about the issues with sockets and heater current, but I'm still on the same set of 6C33's that I started with in my amps (going on 10 years now) and the same pair of sockets. Granted, I bought something other than the cheapest Chinese sockets.
I also agree with 'Mr Blackplate's post.
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