Erik Mandaville Posted December 23, 2003 Share Posted December 23, 2003 Well, this was not as simple as I thought it would be. With the new input tube and plate choke installed, all the original operating points/voltages were way out of whack. With hours of juggling dropping resistors (which didn't always seem to want to obey the Law's of Mr. Ohm)behind me, I've got one channel up in running -- on it's side -- with new 2A3 cathode bias resistors, etc. Turn on buzz was exactly the same as Kudret's DRD, which is a normal SET power-up sound, accompanied by a low-level, very brief slight growl. This then vanishes as it should. So.....this isn't something you just want to decide to do for a fun afternoon project! I also alternately experimented with JFL's grid choke and a more conventional grid to ground resistor, the latter of which was easier to work with, but I have balanced things out with the choke in place. For now.... Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted December 23, 2003 Share Posted December 23, 2003 So, Erik, when does the DRDus schematic get posted? expiring minds want to know. Tom Quote Link to comment Share on other sites More sharing options...
Tubinhard Posted December 23, 2003 Share Posted December 23, 2003 Uh...so how does it sound? Quote Link to comment Share on other sites More sharing options...
leok Posted December 23, 2003 Share Posted December 23, 2003 right, how does it sound. The change looks expensive and hard, and I'm running out of space. If it's really good then I might give it a try. It looks like it has to sound different, in any case, because of the significant change in AC loading on the tube. Leo Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted December 23, 2003 Author Share Posted December 23, 2003 Leo: You are right, there is a considerable difference there. The change was not too expensive -- the cost of the two chokes was about $75. I qualified this with the one I usual use as an excuse: Marie and I almost never eat out, go to parties and spend, etc. The gid choke was already in place, but what I found was the need to increase the input cap before the filter in order to offset a drop in voltage with the new choke in place. It's just becomes such a balancing act. One little change in one part of the circuit does something else, elsewhere -- back and forth and back and forth until some sort of reasonable compromise can be achieved. I've got one amp running, and it's quiet and sounds good! However, this circuit is one that might actually benefit from a capacitor bypass on the input cathode resistor -- I'll have to try it to see...and hear. From one channel working well, there is very good clarity, but music just sounds strange in singl-channel mode. What I want to do is work a little bit more with the cathode bias resistors on the 2A3, where two are used rather than one. As in the DRD, it would function as both the cathode resistor for the output stage, as well as a voltage divider for the 6N1P plate supply. I almost there... Quote Link to comment Share on other sites More sharing options...
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