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Bottlehead Forum Welcome! Need support, you got it. Or share you ideas and experiences. |
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Bottlehead Forum Welcome! Need support, you got it. Or share you ideas and experiences. |
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In Reply to: 845 on a SEX amp? posted by Matts_ on September 17, 2006 at 10:40:38:
Driving the 845 run anywhere upward of 700V is no more difficult
than driving a 300B. You need anywhere from 140-180Vp-p swing
to do the job. Under 700V, its a very inexpensive and very good tube to use and nearly impossible to screw up. If you're building an
845 amp, the driver stage is actually the least of your worries. I'd
be more concerned about how big and how much the PSU parts will be.The legendary "difficulty" with the 845 is when you cross 900V. At
that operating point, a number of design and implementation issues get very messy. For one, a 900V power supply will give you alot of headaches. Second, you need to find someone who can wind the output transformer with the proper insulation materials to take the high
signal voltage levels while not suffering from HF degradation from all the capacitance that comes about with lots of insulation and layers.Finally, you'll need a driver that can slew 400V at 20kHz for the
845's grid. If you try to do that without an interstage transformer, you begin to place alot of trust on coupling capacitors and are forced to use tubes with a high operating point like KT88s and the like.Dont even think you can do a 900V 845 amp on "a budget". The parts
to do it right COST MORE than the budget Chinese amps on Ebay. On the other hand, if you keep it around 700V, you can definitely do up a nice 15W 845 amp and stay within the realm of attainable parts and being able to pull it off without problems.
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Follow Ups
- Any ole' 300B driver will work.... - Jim Doyle 09/17/0616:20:16 09/17/06 (0)
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