Posted by Thrint [ 172.154.180.183 ] on July 31, 2005 at 18:35:07:
For those who don't need any additional gain I ahve an idea. It is even all SS, though the development model is completely valve.
One needs a high gm, low input capacitance device to act like a cathode follower. Some pentodes work quite well, but a pair of DN2540 mosfets rigged in cascode as in the Guinevere plate loads is even better. No set resistor is needed.
Have this device ride on a goooood CCS. Again the Guinevere plate loads will do well, and this time we *WILL* build the complete thing. Set it to sink 10 mA.
Attach the volum pot's wiper to the lower gate, and cap couple from its source( as in Guinevere ).
Supply a +/- 60V set of rails and we're off...low output Z, wideband response, and no silly high voltage capacitors needed.
For parts, a 120V CT power TX, two 10 Hy/100 mA chokes and two good capacitors are all that's required. Figure $100 max if you don't want a gold-plated box...
regards,
Douglas
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