Erik Mandaville Posted August 23, 2003 Share Posted August 23, 2003 I told some that I would post a revised version of Jeff's Horus schematic. I have to thank Edster very much for helping me with what would have been totally impossible for me to do myself -- he has supplied a link to the digitized image. He also gave me instructions on how to post it here, which I would like to do for those who said they would be interested in seeing it. So, let me see if I can get this to work, and then I will explain the small changes I made. Jeff's circuit remains entirely whole, except for a few details which were not included on the original. Also, the Ultrapath (or W.E. connection)shows the bottom of the OPT primary connected to the cathode via the 47Uf. capacitor. On the actual amp, this connection is made at the wiper of the hum null pot. The 2A3 cathode resistor is also NOT bypassed as it is on the original schematic. There is a 'Thanks to Leok' in the area of the Ultrapath output connection. For those of you who have the original, you will notice that mine is a sort of flip-flopped version of the original. Where you see an 'L' in this schematic, it refers to the use of a 'choke.' Certainly this won't be of interest to everyone, but there have been schematic diagrams posted here in recent weeks. Since the Horus had been discussed somewhat at length, I thought I would share the actual circuit. *Note: There have already been some small changes to this, and it is not the final version. The ground connections symbolized by a broken arrow point do not imply a chassis ground connection -- just that the connection is referenced to the ground buss, which is in turn chassis grounded at the BNC/RCA jack -- this is shown with the typical chassis ground symbol. I hope this works for you! If it doesn't work, please email me, and I will send you what my wife called a 'hard link' (whatever that means!). E Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted August 23, 2003 Author Share Posted August 23, 2003 Thanks, Ed! Awesome! *Also shown here, and which is not on the original, is the 1 ohm 5W dropping resistor and extra 10K uf filter capacitor on the 5687 heater supply. I wanted to get this down to as close to 6.3VDC as possible, and am now running these at 6.4 volts with the resistor in place. Without it, I was well over 7 volts. Quote Link to comment Share on other sites More sharing options...
Mallette Posted August 23, 2003 Share Posted August 23, 2003 I'm waiting with baited breath. May have to brush soon... :-) Dave Quote Link to comment Share on other sites More sharing options...
mike stehr Posted August 23, 2003 Share Posted August 23, 2003 Cool! Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted August 23, 2003 Share Posted August 23, 2003 I'm not quite sure how these differ from what I have (modified), but these amps are good for a Woodrow just about any time of day Quote Link to comment Share on other sites More sharing options...
leok Posted August 23, 2003 Share Posted August 23, 2003 Erik, It looks good from here. Did you use 2A3s in your own implementation, or the 6.3V version (the number of which I can't remember) which will accomodate direct connection of the WE cap to the cathode? One of these days I have to try that inductor on the 2A3 grid. leok Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted August 24, 2003 Author Share Posted August 24, 2003 I used 2.5 volt 2A3s. In wishing to keep the schematic as close to Jeff's as possible (his design, afterall), I indicated the same MagneQuest power transformer; which like our Moondogs has a 2.5 volt filament secondary. On my own Horus, I used a Hammond PT which doesn't have that winding. So this required the use of a separate 2.5 V filament transformer. There was a change in value of the 1.5uf input capacitor, too. 1.5uf put B+ quite a bit higher than where I wanted it, and 1uf placed things exactly one volt above the schematic spec. So all the changes were really just to make things work out in our specific situation. Just some small adjustments. The more major change is of course the WE connection. But you know, I have always wanted to try the 6 volt 2A3 heated with DC. Like seemingly every single aspect of this thing, there are differing opinions on the use of AC and DC in directly heated tubes. I about drove myself nuts with some experimenting I started doing with battery supplies on the the 6SN7 and 2A3 heaters. Using 12 volt batteries, I used a series connection on the 6SN7s, which worked fine. What an absolute pain, though -- totally not practical since they had already been using DC and are indirectly heated tubes to begin with. I had wires going all over the place, and my wife was even afraid to turn the system on, since I had installed B+ standby and filament voltage switches. It all worked, but was more an exercise in frustration than convenience. I think there is something special going on with a choke on the 2A3 grid. The MagneQuest part# is listed on the above schematic. Erik Quote Link to comment Share on other sites More sharing options...
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