Layouts

[caglej]

Here are some of the layouts I've been able to find online.........They are not to be taken as reference, but are a good starting point.

[Icetech]

Someone needs to make a clean pretty layout of that bottom one:)

[Funkalicousgroove]

None of them are "correct" They'll all work, but if you want dead-on clones these aren't it. I know that the one that is on loose leaf paper is Steve Ahola's mod to a SF Bassman. If anyone has a good program to do layouts I'd be more than happy to assist, but I don't have the time to do one all by myself.

[Icetech]

Ah thanks for that info.. im actually going to try this in a SF bassman.. but was going to try using the bottom one which i believe is sheltons...

[RossH]

Here is another layout of an OD with reverb that I ran across on the net a while back.

I really have no idea whether this is the original schemo or a different reverb. I have never seen one.

Ross

[oldmacman]

Bottom layout is mine.

The layout is semi-based on the photos of #0040 that have already been posted. The lead dress isn't quite right, and many of the values are wrong. One of these days I'll get around to drawing an updated version.

Ben

[Normster]

First schematic is Steve A's Bassman mod, second is Bob I's, and third is Ben S's. That last layout was one I drew up for a modded Bassman. It has a few errors that I've never corrected, the most significant of which is the V2 coupling cap values are reversed.

The reverb circuit is NOT a dumble circuit. It was based on a design that Gary J came up with and is very similar to the design used on the Pignose G60VR. It only uses a single tube but still gives just enough verb to set the guitar into the mix.

[BobW]

I don't have the full version of Adobe acrobat, so how do I make a VISIO layout of my SF Bassman clone into a jpeg or gif to upload to you guys? I tried copying it into paint, but the file was too large to upload (>5M) BobW

[RossH]

Just SELECT ALL through the EDIT menu or just press CTRL-A and then go to SAVE AS and select under SAVE AS TYPE the JPEG FILE INTERCHANGE FORMAT (.JPG) extension. I usually change the defaulted 75% to 90% under the compression section after you press OK. Then take the file and upload it to here.

HTH,
Ross

[RossH]

Here is another handy option I've run across...

http://www.cutepdf.com/products/cutepdf/Writer.asp

Here you can just print to PDF.

Ross

[BobW]

Thanks, just didn't initially scroll all the way down to find the jpg format.

Anyway, here's my layout of the REV A based on a SF Bassman. I removed the original fiberboard and replaced it with a turret board. Am still tweaking it after 4 months. Mostly in the grid stopper ckt of OD1. the 220pF sounds too gritty, so I recently changed to a .01uF and sounds closer. hth

[dogears]

Bob,

I liked your neat diagrams.

A few observations:

Ditch the weird input network that feeds the OD. Use a 220k over a 100k trim. Don't try and reinvent the wheel.... I have plenty of grail era pics showing 220k over 100k. Just because some 35 year old amp had a weird network doesn't make it the norm or even desireable.

Try a set of 270pf-330pf snubbers on V2. I would not totally remove the V2b snubber. You can always add a 250k pot and .001uf cap from pin 6 to ground to smooth the highs.

Try making your V1b local feedback switchable. You'd be surprised by the increased range you get with no FB.

Raise your OD1 bypass cap to 4.7 or 5uf. I would not run both a 1uf in CL2 and OD2. I HATE that sound. Try one or the other. Or, try 1.5uf A little extra goes a long way.

Along the lines of my last point, try a .02uf CL2 cap. That way, you can use the bigger bypass caps. Better tone IMO.

Try a 300pf treble cap. Measure the ceramic. A tad smaller than 330pf sounds nice to me.

Experiment with the grid bypass on the 220k V1b grid resistor. Some amps had none, and others had as much as 500pf. Most I have seen had 500pf.

Try increasing the PI plates to 100k and 110k

You have a 47pf bright cap on the master. If you have one global master, this is way big, imho. Try a 10pf or 15pf instead.

Let me know if you try any of these suggestions.

[BobW]

Dogears, excellent suggestions, a few, but not all, I've tried. Agree, the bright cap is way too bright, and may be the reason why I was trying to tame it elsewhere, and may explain why the initial 200K over the 100k pot didn't help. Was inadvertenly trying LP filters, into the bad mode of more than 1 mod/change at a time, and basically chasing my tail. Will let you know the results when tweaked. I appreciate the help!

[Icetech]

Bobw, this will sound odd.. but would you happen to have the part #'s for the push/pulls you used? I look at mouser and digikey and get lost in a hurry..

[BobW]

Dogears, Here's what I've tried,

OD1 snubber 360pF
OD2 snubber 250pF
cathode caps 4.7, 4.7, 4.7+1, 1+1.
I may add a switch to one of the 1ufs on the last stage, it sounds great either way.
The best improvement was the .047 change to a .02 on CL2, made a huge difference.
Next I'll try a .005 at OD2, 10-15pF bright cap.
No real difference in the PI plate changes from 100K/110K to what was there. I redialed in the initial values w/pot.
Didn't change the odd network input yet, probably tonight.
Overall it's improved, will keep prodding when time allows.