Tweed Bassman 5b6 50w head started

[M Fowler]

I'm laying out the drill pattern for a 50w version of the early octal Bassman 5b6 with fixed bias.

Transformers are MC Bassman OT 40-18001 4k2 4/8/16
MC Bassman PT 40-18029 710vct 200mA
I'm seriously considering a choke.

I'm positioning the rectifier and power tubes to be in the rear so one can change them out easier and so they cool better. Using 12x8x2.5 chassis in Mikey head cabinet.
I think I will go PTP on this one.

I'm going to workup ideas for a KT88 version as well using Dynaco Iron.

Mark

[JazzGuitarGimp]

I'm looking forward to watching this one progress!

[BarryW]

I'm doing one of these as well, with very similar iron. I haven't decided if I'll do PTP, tagstrips or what for this one - probably basic tagstrips as I've been doing a lot of amps with those lately.

[Phil_S]

I've been staring at the schematic and layout drawing thinking I'm going to get on the bandwagon and build one, too. I don't like the layout. It is designed for the control panel separate from the chassis and for use in a combo. I want to build a head.

What I don't like and want to change:
-move the 5881's (6L6's) next to the rectifier.
-move the filter cap for the 6SL7 and 6SC7 downstream so I can ground it with the cathodes of the 6SL7.
-untangle some of the wiring, seems to me 6SL7 into the power section could be cleaned up.
-only need a single input; thinking I'll just parallel the sections of the 6SC7, but not sure of the tonal implications.
-collect up the grounds in a scheme that is more to my liking...ground buss for the preamps, gang the power tubes directly to the chassis, something like that.

Maybe it isn't broken and I shouldn't fix this?

Is there a new and improved layout floating around? I'd be grateful to have a look. I've made several attempts to rework the layout but I'm not happy with it.

Also, I"m working with pencil and paper. I keep having bad luck with Inkscape shutting down without notice. Is there other freeware out there for layout? As you know, it is better to be able to move stuff around electronically.

Thanks any advice.

Phil

[M Fowler]

http://ampgarage.com/forum/download/file.php?id=25831

This is how I converted the original Fender 5b6 layout to a working head amp in a Princeton style slant face chassis.

But I think some steel guitar guys are trying to get a Little Walter looking head with that tone on a shoestring budget and I don't blame them.

[Phil_S]

That's elegantly simple, Mark. I am overthinking this. I might want to move some of the stuff for the 2nd section of the 6SL7 to the other side so I don't have so many crossed wires. I see I was on the right track, flipping the B+ to the other side of the board for V1, V2.

Did you add screen stoppers for the power tubes? What value? I can't quite make out the resistors on the terminal strips at that spot. I can see the black ones going to the screen supply, so those are screen stoppers.

What value are the striped ones on V3, V4 and where to they connect? Are there the grid leak R's?

I notice you avoid under board wiring. I think I know why. BTDT, LOL!

Thanks very much.

Phil

[M Fowler]

Phil I will get to your questions soon.

Cut PT hole and punched for tube sockets. Lots of small holes left.

[M Fowler]

That's elegantly simple, Mark. I am overthinking this. I might want to move some of the stuff for the 2nd section of the 6SL7 to the other side so I don't have so many crossed wires. I see I was on the right track, flipping the B+ to the other side of the board for V1, V2.

Did you add screen stoppers for the power tubes? What value? I can't quite make out the resistors on the terminal strips at that spot. I can see the black ones going to the screen supply, so those are screen stoppers.

What value are the striped ones on V3, V4 and where to they connect? Are there the grid leak R's?

I notice you avoid under board wiring. I think I know why. BTDT, LOL!

Thanks very much.

Phil

1k CF on grids and 1k5 Dale on screens on the 6L6GC (actually 470R on the screens) EDITED

Poor layout attached, maybe a pro visio guy could make a layout for TAG.

[Phil_S]

Thanks, Mark. I've been working on the layout in Inkscape. Only once it folded on me tonight. Tedious, but good planning is worth it. Your picture was a huge help. It is yet to be determined if my layout is improved or not. I will post for comments when done. It could be several days or a week.

Phil

[Phil_S]

As I said, I've been drawing a 5B6 layout in Inkscape. It may be that my skill with the program isn't very good, but I am finding it very time consuming to use and rather unforgiving. OTOH, it is freeware, so I shouldn't complain. I have omitting a number of things like the PT and OT. I see I forgot to show the main filters grounded to the chassis. The 6800+25 NFB loop is incomplete as I wasn't sure where to ground the 25R and 6K8 is floating because I don't have the output jack in the layout. Without the OT and PT, wiring for the power tubes is incomplete. A moderately experienced builder should be able to get past what I've omitted.

In any case, if you'd like to critique the substance of it rather than what's omitted intentionally, I'd like to hear your comments.

In previewing, double clicking the drawing, Firefox is identifying this as an attack site. I assure you, it is OK to bypass the warning! I suppose the mods will eventually get this smoothed out.

Thanks.

Phil

Edit: Updated drawing 25 Jan 2013; crude additions of what was missing.

[M Fowler]

Phil nice job.

I was in my blonde 5b6 chassis and the power tube grids are 1k and the screens are 470R sorry about that.

Mark

[Phil_S]

Thanks, Mark. I filled in some missing parts!

[M Fowler]

Finished up the board today.

This will be a fixed bias version not cathode bias.

[M Fowler]

I had to redo my board to tie the two 270k bias resistors to the bias pot.

I had them going to ground for cathode bias configuration, I'll post new board picture soon.

Mark

[M Fowler]

Got some more done yesterday and today.