I picked up another amp. I want to mod this for guitar and was thinking about removing V1 & V2 and connecting my input to pin 4 of V3 but the plate voltage seem odd . I replaced the 6sn7GT's (12au7ish) with 12SL7GT's(12ax7ish) for more gain . Do i need to install a new preamp or can i mod this amp and good results.
thanks
Baddog
Last edited by tboy; 03-03-2009 at 08:24 AM.
I have a '57 AU-33 that used to have 3 mic inputs. I cascaded two of the input pentodes and left the 3rd channel (and everything else) stock. A/B switch between the two inputs. I've used it with the band and it sounds really good, but could use some more tweaking and it's on the back burner for now. I have a bunch of stuff like that.
check out my Myspace page for pics of some of my stuff
http://viewmorepics.myspace.com/inde...albumId=580437
BD
I have an SC-58B that I purchased on ebay a year ago. Would you be able to send me a copy of the schem? I replaced the electrolytics, and coupling caps to better suit a guitar amp, and did some cosmetic changes. I also changed out the 6sn7 for 6sl7's, but the high frequency response is not enough.
Let me know if you want to see pics. I'm new to homebrewing and have a lot to learn still.
Last edited by tboy; 03-03-2009 at 08:25 AM.
I meant AU-58B
Not a problem
Let me now if this helps . If you want to send me your email address in a private message ,i can send one to your home page.
BD
Post pics . we like pics
Pic...
Here is a video of the amp in action. Myspace
http://vids.myspace.com/index.cfm?fu...=vids.myvideos
And pics
http://viewmorepics.myspace.com/inde...ndID=442868709
BD
Last edited by baddog; 03-19-2009 at 02:29 AM.
Nice Baddog, you added a standby. I'm not a My Space member and I wasn't able to view/listen.
I replaced the 6SN7's to 6SL7's and it added more clarity and punch.
Thanks
Im glad it worked out for you. A stndby is nice to have and it was easy to do.
Baddog
Dave, I have done the same to my 33, have the mic 1 as a clean channel and mic 2 & 3 together with the vol on 2 as the gain/distortion pot and 3 as the master. It just so happened when the two are tied together( plate of two to grid of three, jack to grid connection for three removed) the volumes are indpendent and 2 distorts signal going into 3, which is a cool thing. Volume on 3 is a good master control. I changed the values of the plate and cathode resistors to tame down the gain a bit on both valves, seems to have real crunch now with pot 2 at 12 and 3 at 3. This thing will scream if pot 3 is turned past 6, starts to get into fuzz territory and breaks up some beyond this, lows rattle a little and not as quality a fuzz as a pedal. Can give you the values on the resistors in it right now if you still have it and care to work on it. Have run this for hours at a time and the trannys and tubes are all fine. Need to cherry pick the 6sf5 though, there are more microphonic ones out there than not. let me know.
Yes, I still have it, and I'm interested in what you've done to yours. All I did was cascade a pair, and haven't really tweaked it much. I've been playing bass lately, (in a couple bands) and most of my personal projects are always on the back burner. I have some good 6SF5 tubes (GT, IIRC). Actually, this might make a decent little bass amp run stock. Hmmm.
For the "lows rattle a little", try tweaking the coupling cap(s) smaller. Do the "one at a time" method and in different places in that channel; you'll probably only need to do the first one (between the first two stages). Maybe I'll get some time to mess with it more. There's a local harp player that's interested in it, and he likes a LOT of grit... I'm not sure I'd part with it.
Dave hope this is not too cluttered to use when it arrives.
And here's an original (well, sorta) for your file.
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