Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 yep, looks fine. Oh, as far as floating one cathode of the parallel triodes, I have no idea if that will be okay or cause some trouble. Never tried that. Well, I guess I'll find out... Here's the first stages and the Bass & Treble EQ. I will add the midrange EQ on the next page of the schematic. I would think () that if the cathodes are not bridged, (open SW2) and the cathode on the boost side is open and floating it should be OK though. The other option would be to use a 3PST and just bridge the cathodes, the grids and the anodes with one throw which would instantly parallel the two triodes. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 18, 2010 Members Share Posted October 18, 2010 missing a resistor at the bottom end of your bass pot, Casey. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 missing a resistor at the bottom end of your bass pot, Casey. Ooops, I erased it by accident when I was revising this thanks... It's R24 = 22k I revised the schematic and I 'll post it tomorrow, it's 3:35 Am and I am going to bed. (I'm getting punchy) Thaks for the help. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 Here's the latest revision of this part of the schematic. I added mixing resistors at the junction of C1 & C9 (R26 & R27) and a grid leak resistor (R25) at V2a. I put the resistor back on my bass pot (R24). Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 18, 2010 Members Share Posted October 18, 2010 I see a problem with the EQ section. The cathode of V3a will idle at about 10~15v, depending on the B+. Not sure if the plate dissipation will exceed the rating on a 12AX7, but it will be pretty warm. The real problem happens in the Bass control. You aren't using a coupling capacitor. So most of this voltage will be dropped across the bass pot. As you turn the bass control up, you'll also increase the voltage that the grid of V3b is referenced to. The idle current of V3b will vary widely. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 I see a problem with the EQ section. The cathode of V3a will idle at about 10~15v, depending on the B+. Not sure if the plate dissipation will exceed the rating on a 12AX7, but it will be pretty warm. Maybe that is what that ohter guy was trying to tell me... The real problem happens in the Bass control. You aren't using a coupling capacitor. So most of this voltage will be dropped across the bass pot. As you turn the bass control up, you'll also increase the voltage that the grid of V3b is referenced to. The idle current of V3b will vary widely. I thought that was what C8 was doing. Or do you meanbetween V3a K and R19? The EQ is pretty much verbatum RCA Baxandall design but i realize it's going to take a little tweaking. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 18, 2010 Members Share Posted October 18, 2010 Or do you meanbetween V3a K and R19?Yes, that's exactly what I mean. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 Yes, that's exactly what I mean. OK I just added a .022 coupling cap there. One thing at a time, and this is starting to come together. Once I have a decent pre-amp design the power amp and PI is a breeze, as is the reverb circuit. The power supply is essentially finished except for the bleeder resistor and looking into putting that 6.3V CT onto a 50VDC source. I just got a link to some free CAD ware for schematics I might try. I haven't had much success with CAD so far, but my crude schematics freak some people out. And I might get the whole amp on a single sheet of paper instead of the 3 or 4 pages this will take. . Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 Here's the 4th revision of the front of the preamp. Link to comment Share on other sites More sharing options...
Members Zozobra Posted October 18, 2010 Members Share Posted October 18, 2010 ExpressSCH/PCB is what I use. It doesnt have tubes in as standard but making components is easy enough. I've made a generic triode that I can pass on if you're using this package. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 18, 2010 Author Members Share Posted October 18, 2010 ExpressSCH/PCB is what I use. It doesnt have tubes in as standard but making components is easy enough. I've made a generic triode that I can pass on if you're using this package. Thanks a bunch I just downloded that program a few hours ago and I haven't had much time to try it out yet. But thanks, if I get the hang of this I'll get those symbols from you. I will probably still continue to do it with a pencil ... Old Geezers and computers don't always agree on things LOL, so we shall see. Link to comment Share on other sites More sharing options...
Members Zozobra Posted October 18, 2010 Members Share Posted October 18, 2010 The learning curve isn't too bad. It does do a few odd things though. I still get ideas down on paper to start with and then break out the cad software later. The main advantage for me is that it automatically numbers components and generates a bill of components as if I did it by hand I'd screw it up. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 19, 2010 Author Members Share Posted October 19, 2010 This is Revision #5. I am getting a few things ironed out as I go. There is no point in starting on the next couple of sections until I am satisfied with this section. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 19, 2010 Author Members Share Posted October 19, 2010 The learning curve isn't too bad. It does do a few odd things though. I still get ideas down on paper to start with and then break out the cad software later. The main advantage for me is that it automatically numbers components and generates a bill of components as if I did it by hand I'd screw it up. I'm working on this, but I get fustrated. I was a draftsman for an engineering company in 1967-68 so I am accostomed to hand drawn schematics. I like the "intimacy" of hand drawing my schematics since I am going to be the builder. BUT, I would like to be a bit neater and I have trouble getting everything on a standard piece of paper to copy and scan. I am still working on that program but there are some things a 63 year old just isn't going to master this late in the game LOL.... Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 20, 2010 Author Members Share Posted October 20, 2010 Here's my first CAD attempt, but it took me almost 5 hours to copy from my first schematic. I still have lot to learn yet but I think I am finally getting there. EDIT: Revised copy Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 20, 2010 Author Members Share Posted October 20, 2010 Here's revision VI Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 21, 2010 Members Share Posted October 21, 2010 That's an interesting twist you have with the paralleled triodes, Casey. It looks similar to something Chris Muir was talking about the last time I chatted with him. I like what you've done with the 1Meg resistor to keep the DC applied to the additional bypass cap (C16), even when it's "out" of the circuit. You should use the same technique on C7. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 21, 2010 Author Members Share Posted October 21, 2010 That's an interesting twist you have with the paralleled triodes, Casey. It looks similar to something Chris Muir was talking about the last time I chatted with him. I like what you've done with the 1Meg resistor to keep the DC applied to the additional bypass cap (C16), even when it's "out" of the circuit. You should use the same technique on C7. Yeah I migh tdo that to both of the other switches, it's to minimize "POP". I just ordered some DP3T switches (on-on-on) for the midrange control, where there are the selections for the inductor. But, I finally finished the whole pre amp section with reverb. I will have to make a seperate sheet for the values etc, there just isn't enough room on this page anymore. V1, V2, V3, and V5 are 12AX7 / 7025 V4 is 12AU7 or 12AY7 V6 is 12AT7 V7 is 12AT7 the PI on the next page Thats 7, 9A tubes, it's a good thing my PT is rated at 250ma. Link to comment Share on other sites More sharing options...
Members sidonia123 Posted October 21, 2010 Members Share Posted October 21, 2010 Nice tip! I will do that. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 21, 2010 Author Members Share Posted October 21, 2010 Nice tip! I will do that. I do intend to use a couple of relays to switch the boost on with a foot control along with the reverb. I, at this point, don't want to draw all that in because this schematic is busy enough. I am going to draw some attachments for some of that kind of thing. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 21, 2010 Members Share Posted October 21, 2010 Thats 7, 9A tubes, it's a good thing my PT is rated at 250ma. Current on the B+ supply usually isn't much of a concern with lots of 9A tubes. Figuring a generous 2mA per triode, that's 28mA for all 7. Each of your 5881s will idle at much more current than that. Heaters are another matter, though. 300mA per tube. That's just over 2 amps for all 7. This is slightly more than both of your 5881s put together. I hope your 6v winding is rated for 4A or more. Btw, sidonia123 was a sigspambot. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 21, 2010 Author Members Share Posted October 21, 2010 Current on the B+ supply usually isn't much of a concern with lots of 9A tubes. Figuring a generous 2mA per triode, that's 28mA for all 7. Each of your 5881s will idle at much more current than that. Heaters are another matter, though. 300mA per tube. That's just over 2 amps for all 7. This is slightly more than both of your 5881s put together. I hope your 6v winding is rated for 4A or more. Btw, sidonia123 was a sigspambot. I always allow plenty for the current, I designed with about 5ma for each tube thats 2.5 per side. Thats a little overkill but it gives me wiggle room incase I have missed something. My 6.3 winding is rated at 5A, as is the 5V wnding. I am going to remove the "sag" resistor on the SS supply for a more dramatic change. I am also removing the strap between the cathodes on V2 and add 1M resistors to some of the other switches. Looking at the V4 schematic, how did I do with the inductor switching? Those slide switches are a bit confusing, but I only see three choices, I have ordered the miniture switches for everthing. I will use standard size switches for the on/off and standby. I have also been getting some good suggestions from a guy on Ampage, like the resistor accross some of these switches. You should drop by that forum and read some of the interesting stuff there. (not AmpGarage BTW) http://music-electronics-forum.com/f10/ Look for "Theroy and Design". I have absolutly no Idea what a "sigspambot" means. Is that an automated thing? Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 21, 2010 Members Share Posted October 21, 2010 Looking at the V4 schematic, how did I do with the inductor switching? Those slide switches are a bit confusing, but I only see three choices, I have ordered the miniture switches for everthing. I will use standard size switches for the on/off and standby.The lleft side of the drawing below shows the internal connections (red lines) that happen in each position of a DPDT on-on-on switch. What you need to replace that slide switch is a SP3T switch. Your switch might already have a jumper installed externally (blue), else you will need to add it. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 21, 2010 Author Members Share Posted October 21, 2010 I ordered some DP3T switches, and some DPDT switches I can use universally for the other stuff. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190458831729&ssPageName=STRK:MEWNX:IT How could you tell that was fake post? Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 21, 2010 Members Share Posted October 21, 2010 I can't say for sure from the view in the photo, but it looks like those switches will be like what's on the left in my drawing. It will be easy enough to tell with an ohmmeter when you have them in your hands. The guy was easy enough to spot when his sig was up. Ad links for china stuff. And look at the very beginning of his post. He forgot to edit out ^ the first quote tag when he copy/quoted your post. Link to comment Share on other sites More sharing options...
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