Posted by Tnuctip [ 64.12.116.14 ] on December 21, 2004 at 17:41:47:
In Reply to: Re: that's what I thought you meant... posted by colinhester on December 21, 2004 at 17:06:10:
Hey-Hey!!!,
Seems reasonable...
Take a slightly smaller simpler means of doing it.
180vac( or thereabouts, there is a 190-0190 Hammond, 2 or 369EX ), double for a CT winding or a full bridge on a single...hybrid bridge, SF4007 diodes to ground and a 6CA4 for the forward diodes. The same 30 Hy Hammond, and an eaBay-ed motor run of 240vac rating and ~100 uF.
This will get a reasonable B+. The single DN2540N5 with a reasonable heatsink will also allow the use of another output point, namely the source of the MOSFET. You'll have what is effectively a source follower output buffer. This also simplifies the cathode circuit because the triode still sees a constant curent, and no bypass is needed. Use a pot instead of a fixed resistor to set the current. try 10-15 mA.
The output coupling cap has already been mentioned.
the EX Hammond has 2.5A of 6.3, plenty for a 6CA4 and single 5687. DC can be done with a RadioShack TX and an LM317 should it be required at ~$20 additional.
Biasing of ~3 volts ought to give a good operating point, 2-4v is a good place to play. V=iR.
so, 2 nine pin sockets, 1 5687, 1 6CA4, 1 369EX( note 370AX is on sale for $36 ), 1 157G, one 80-100 uF/240vac motor run oiler, 2 5 uF motor run caps for the output coupling, 2 DN2540N5 mosfets, 510R 1/4 watt carbon comp gate stoppers, 2 1kOhm pots for current set, 4 RCA jacks, 1 stereo volume control ( R-S 100k Alps is ~$3 ), 4 red/20 mA LED's for bias, wire and chassis material.
so where are we?
regards,
Douglas
....damned Thrintun!
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