Members Slunderfungus Posted October 24, 2010 Members Share Posted October 24, 2010 I am building 5E4-A Fender Super Amp into an old Integrated amp chassis...its gonna be one heavy,HEAVY anp in a compact little package:freak: I have reached another one of those:facepalm:moments where I can't think of how to make this go forward. I am using a Magnetic Concepts power tranny for 18-20 watt that has this layout: http://classictone.net/40-18035.pdf The 5E4 is a fixed bias circuit if I'm not mistaken and Fender amps use a PT that has a seperate lead of the HT winding for the bias circuit. Can I still make this thing fixed bias or am I going to have to go cathode bias with this mama? Also I want to know how to lace in the B+ voltage.Do I just run a wire from pin 8 of the rectifier to the main filter? The way the schematics show this, is one 5volt lead goes to pin 2 then the other 5 volt lead goes straight to the main filter while jumper from pin 8 meets this one mid way. I am also wanting to know where the middle wire on my OT goes. On the front of it there are the two leads which go to the plates of the power tubes. The middle wire just shows it is, or goes to 8K ohms:idk: When looking at the schematic it seems that this lead also goes to the Filter circuit...hmmm, maybe to get power to the OT?...that only just came to mind. On the schematic it shows this wire also goes to the power tubes but does not specify which pin. I have been finding Fenders schematics very vague about such details when compared to schematics I have from Photofact folders on different amps. I hope this series of questions is clear, if not let me know and I will try to clarify. Thanks,Dan _____________________________-edit-_____________________________ I figure it might be easier if I posted the schematic and layout, since I found them on the web for just such occasions! On another note, I am working with a pretty compact chassis and so was only going to use 2 inputs. Is it posseble to blend the two channels so that I can use the side of the 12ax7 that the second set of inputs would otherwise be using? Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 24, 2010 Members Share Posted October 24, 2010 I am building 5E4-A Fender Super Amp into an old Integrated amp chassis...its gonna be one heavy,HEAVY anp in a compact little package:freak: I have reached another one of those:facepalm:moments where I can't think of how to make this go forward. I am using a Magnet Concepts power tranny for 18-20 watt that has this layout:http://classictone.net/40-18035.pdfThe 5E4 is a fixed bias circuit if I'm not mistaken and Fender amps use a PT that has a seperate lead of the HT winding for the bias circuit. Can I still make this thing fixed bias or am I going to have to go cathode bias with this mama? All you have to do is pull the bias feed from one side of the mains. Take a look at the power supply in the last post in my winter amp thread... Just like that. Also I want to know how to lace in the B+ voltage.Do I just run a wire from pin 8 of the rectifier to the main filter? Yes that's all there is to it. The way the schematics show this, is one 5volt lead goes to pin 2 then the other 5 volt lead goes straight to the main filter while jumper from pin 8 meets this one mid way. The 5V rectifier heater wires go to pins 2 & 8, then from pin 8 to the first cap. I am also wanting to know where the middle wire on my OT goes. On the front of it there are the two leads which go to the plates of the power tubes. The middle wire just shows it is, or goes to 8K ohms:idk: When looking at the schematic it seems that this lead also goes to the Filter circuit...hmmm, maybe to get power to the OT?...that only just came to mind. On the schematic it shows this wire also goes to the power tubes but does not specify which pin. I have been finding Fenders schematics very vague about such details when compared to schematics I have from Photofact folders on different amps. The CT of the OT goes to your first power point in the supply, which is generally marked as "A". The other two wires go to pin 3 on the power tubes, that is your plates. I hope this series of questions is clear, if not let me know and I will try to clarify. Thanks,Dan Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 24, 2010 Members Share Posted October 24, 2010 Here's a sketch for you on the bias supply Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 24, 2010 Members Share Posted October 24, 2010 Casey handled the other questions, so I'll just focus on these two... On another note, I am working with a pretty compact chassis and so was only going to use 2 inputs. Is it posseble to blend the two channels so that I can use the side of the 12ax7 that the second set of inputs would otherwise be using?Yes. The easiest way of doing that is to pick one channel as being the default "blend" input, when nothing is connected to the other jack. For instance, if you pick channel 1 (top of the drawing) as being the "blend" or master input, you would connect the tip of that jack to the switched part of the input jack on the second (slave) input. When you only have a plug inserted in channel 1, both inputs are in parallel. Both volume controls will affect the same signal plugged into channel 1. But when you insert a plug into channel 2, both channels will be independent. If you only have something plugged into channel 2, only the bottom volume control will do anything. If you also connect another guitar into channel 1, each guitar will have its own volume control on the amp. Or you can wire it so channel 2 is the master (blend) and channel 1 is the "slave". Whichever you prefer. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 25, 2010 Members Share Posted October 25, 2010 The Deluxe 6G3 schematic shows a similar bias supply off of one of the mains similar to my drawing, but without the adjustment pot. http://www.el34world.com/charts/Schematics/files/fender/deluxe_6g3_schem.pdf EDIT, change the dropping resistor from 82K to 100K if the -Voltage is too high. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 25, 2010 Members Share Posted October 25, 2010 SYK, I was thinking about your answer above and I have a question. Do you still share the cathode bias like the original schematic? I can't see why not unless you wanted to "voice" the cathodes differently, which might be intresting. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 25, 2010 Author Members Share Posted October 25, 2010 Casey handled the other questions, so I'll just focus on these two...The CT of your OT connects to the B+ after the choke and also to the screen grids of both 6V6s (pin 4). Thank you, the schematic showed it going to the power tubes but didn't specify which pin. Also concerning the choke, I only just realized that there is suppossed to be a choke here:facepalm:I know chokes come in all manner of strengths, how would I go about findingthe proper choke for this application? I happen to have an 85 ohm/1500V that has been in lying around. And thanks Casey for the info as well. Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 25, 2010 Members Share Posted October 25, 2010 Use the basic Fender choke right there, it's 4 Henries and 108 ohms. The Fender part number is 125C1A and is about $13.00 at AES. http://www.tubesandmore.com/ Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 25, 2010 Members Share Posted October 25, 2010 Thank you, the schematic showed it going to the power tubes but didn't specify which pin. Also concerning the choke, I only just realized that there is suppossed to be a choke here:facepalm:I know chokes come in all manner of strengths, how would I go about findingthe proper choke for this application? I happen to have an 85 ohm/1500V that has been in lying around. And thanks Casey for the info as well. I found the pin number for the screens by comparing the schematic to the layout drawing. You don't absolutely have to have the choke, but it will smooth things out a ton more than just using a 100 ohm resistor. I see Casey has a source for you. I guess we're tag-teaming this one. Here, have a couple of drawings. You can probably reason out what's happening with the inputs, but don't hesitate to ask, if there is anything that isn't crystal clear. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 25, 2010 Author Members Share Posted October 25, 2010 One of the problems with running the two channels, is the fact that I'm working with such a compact chassis. I only have enough room on the face for the Prescence, Bass,Treble, and Volume pots. In fact I am using a On/Off/1M pot so I can keep the on switch on the front of the amp. In fact the pilot light is sitting just a cunt hair over the rectifier socket. I have the Standby switch on the back next to the fuse, so I figured if I can just make it a one input amp and use the rest of that preamp tube for an additional gain stage for the 1st channel. In fact its so cramped that I mounted the filter caps over the OT with a set of 8 lug terminal strips, and the bias board is mounted on the side of the chassis leaving enough room to utilize the original amps hum control as a bias pot:thu: This is how much room I'm working with: I have another pot mounted in the extra input hole because I am thinking on adding a master volume...after I have it working and all the bugs worked out... I left the wires of the PT long only for the time being. On the off chance I want to go with another PT later, I'd like to have enough leads left to still use this PT in a Marshall clone later on. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 25, 2010 Members Share Posted October 25, 2010 so I figured if I can just make it a one input amp and use the rest of that preamp tube for an additional gain stage for the 1st channel.I think i see where you're headed with this. You don't want to "blend" the paralleled triodes. You want to cascade one into the other, right? Like maybe have the first channel feeding the second for additional gain. Or plug into the second channel instead, and that bypasses the first channel completely for normal gain? Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 25, 2010 Author Members Share Posted October 25, 2010 Basically just have a single channel amp, and use the leftover triodes for gainstages...or, Iguess gain stage would be more to the point as it looks like that second channel is only using one side of the last 12ax7:idk: Would an 85 ohm choke work? Link to comment Share on other sites More sharing options...
Members Zozobra Posted October 25, 2010 Members Share Posted October 25, 2010 Wow, that really is a compact chassis Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 25, 2010 Members Share Posted October 25, 2010 Would an 85 ohm choke work? yeah. it won't drop as much voltage so your B+ will be a few volts higher. dunno what the inductance of your choke is or what it should be. more inductance will do a better job of filtering. if your choke can handle the current requirements, you should be okay. everything is going through the choke on this amp, even the plate supply. so it might be about 100 mA total. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 25, 2010 Author Members Share Posted October 25, 2010 Eh...I'll just go ahead an get choke through one of the on line parts houses. At the point that I am now even if I were to finish this amp today I would still be waiting to fire it up. My variac I got used and it was missing the guts inside the receptacle. I finally found the part for it through mouser.com and have to wait til the 1st to get it, so might as well do it right:thu: I haven't skimped anywhere on this build yet and it seems that would be a poor place to start. Wow, that really is a compact chassis Yeah, and it weighs a ton!!! I'm using a big peice of iron for the OT...For a Marshall 45watt JTM:cop: I was looking all oevr for an older style OT with closed bells and 4 point mount, then I ran across this one and thought...fuck it close enough to the existing bolt pattern to rock it for me. When I first started this project last year it was goingto be a Marshall 18 watt clone. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 25, 2010 Members Share Posted October 25, 2010 ya might wanna buy a shoehorn so you can fit the choke onto the chassis somewhere. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 25, 2010 Author Members Share Posted October 25, 2010 There's a place on top, where the filter caps used to be in one of those 40/10/10/10 multi cap cans. The choke could go right there... In fact you can see the spot right in front of where I have the filter caps now. Oh yeah SFK, what would be the easiest way of using the extra triode as an additional gain stage? It may change the amp a bit, but if its a good change, all the better. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 25, 2010 Members Share Posted October 25, 2010 Just yankin your chain, bro. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 26, 2010 Author Members Share Posted October 26, 2010 I was also wondering if this master volume would be doable with my circuit: Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 26, 2010 Members Share Posted October 26, 2010 That's a Pre PI master, and it is certianly doable, but a post PI master is a better system. I was going to do a pre PI master on my new build but SYK suggested the post PI which I went to. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 26, 2010 Author Members Share Posted October 26, 2010 I'm having a harrd time finding a good master volume circuit to copy:facepalm: Link to comment Share on other sites More sharing options...
Members Casey4s Posted October 26, 2010 Members Share Posted October 26, 2010 Look at the one on my project amp. I got that from SYK and I am incorporating that into my build but it will work fine with your build too. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 26, 2010 Members Share Posted October 26, 2010 This is not my drawing, but this guy had exactly the same idea, and added a couple of 2.2Meg resistors. (very smart addition) Basically the dual-ganged 250k pot replaces the 220k resistors that are used to connect the grids to the bias supply. Link to comment Share on other sites More sharing options...
Members Slunderfungus Posted October 26, 2010 Author Members Share Posted October 26, 2010 YEEEEEES!!!!!! I have a dual gang 250k pot left ove fom this amps original form and the pots are small enough in diamter to juuuuuuust fit where I want to put it. snuggled in between the bias feed, the ground lug for my speaker jacks and the wall:facepalm: Yeeep, tiny little chassis. I've named it The Brick:cop: small and heavy...too bad Groove Tubes already trademarked that name... Thanks both of you Casey & SYK the wealth and knowledge you two have is an invaluable asset to HC. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted October 26, 2010 Members Share Posted October 26, 2010 Cheers, Slu. Casey knows quite a few things i'm not so familiar with. And vice versa. So it's been fun working with him. And with you. I sense a possibility of seeing a lot more amp-build activity here in HC DIY. And there are a few other guys who pop in from time to time. I think we have the start of something good. The Brick is taken, how about The Chunk? Link to comment Share on other sites More sharing options...
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