6MB8 Mini-Bassman Standard

[sluckey]

Ed, get a spell checker buddy! 

[Ed_Chambley]

Ed, get a spell checker buddy! 

Typing on a stupid pad. Sorry.
Should be better now. I just think i am too danm old to use a touch screen. You know I really do spell well. I am a writer and graphic designer. I know it is hard to believe.

[purpletele]

Not to seem rude as we all have builds that we chase problems with noise from one place or another.


That being said, and I have done this, I would get out a solder sucker and a hot iron and dissemble. Move that board away from the pots and input jacks. . Enough to install a preamp buss fot grounding. It is not necessary to solder to the back of the pots, but it works. I have never done it.


You may get too close to the tube sockets. Looking at what you have, I can see a number of places where hum could be an issue.


I know it sucks to consider this, but I try to think of it as simply learning. If I am building a high gain preamp my grounding is not  the same as a fender. I use a star component layout which will make your leads short as possible.


Again, not dissing you, but if you want a trouble free amp for years to come, you should follow proven layout methods. Too much loose lead dress and flipping your ground from one side of the board to the other, which it appears you have done is asking for hum.


You may end up with some additiomal holes in the chassis, but if you would like I will be happy to post a photo of a build I made backwards, initially. I just thought, I will make it work. Well I chased one noise after the other until I, took it apart. Made a drawing that followed proven methods.


That was my first Marshall build. Have not had a problem with the amp since.


Just my opinion and it ain't worth near as much as the previous posters so please ignore any or, all is this.

Ed, thanks,

I decided yesterday that was going to do some reorganization to the layout which includes moving all of the tube sockets to allow me to move the board south.  I wrestled with the layout and troubleshooting was difficult. 

I am going to re-work the circuit the Geezer Mini-Bassman schematic.  I was really looking for a smooth circuit with some headroom to get the feel of the 6BM8 tubes and I think the Mini Bassman tone stack might be the ticket for this experiment.

With a little work I can make the amp much more user friendly for my experiments with the 6BM8 tube.

Please send me the photos of your Marshall build, I am interested in the steps that you took to get stuck and the modifications to the layout that benefited the build.

Brian Vallis
otis8@sbcglobal.net

[Ed_Chambley]

Will do, but I but will be later.


In a nutshell, I cut the bottom off the chassis and I welded, and I but have seen them bolted. What I did was drilled the tubes backwards. Had the PT where it should be on a tube down and the tubes up. 


I will show this build and you can have a good laugh, and but Sluckey is not allowed to look. Tubenit and Joe Joe are OK to look. 


I will also post how I now do it, which is better. Actually, I now have 2 methods. One for low gain which is buss bar to input for preamp and transformer bolt for power. I use Merlins star for high gain since it incorporates caps right at the node. The simple reason I don't always do it this way is it is a little more time consuming and a lot of times it just is not needed.


Glad you are considering doing this. You will be much happier in the end.

[purpletele]

I will show this build and you can have a good laugh, and but Sluckey is not allowed to look. Tubenit and Joe Joe are OK to look. 

Thanks Ed,

I am looking forward to see your evolution of style.

[PRR]

> i am too danm old to use a touch screen.

BlueTooth keyboard.

Seriously. I could NOT manage passwords on the Android, and more than a few words kerekty tipped wuzz impozzible. I got a $50 Logitech and a $13 no-name. Both beat piss out of fat fingers on glass.

https://www.logitech.com/en-us/product/multi-device-keyboard-k480 (huh, WalMart charged me full price)

https://www.amazon.com/gp/product/B00NOE7412 (price dropped $2)

[Ledzepp007]

I am not a person to be relied on for amp building advice, but I'm guessing you have grounding issues.

The quietest and best amp I have built was a homebrew that relied on two grounding points, one for the preamp and one for the power amp. Works awesome. Ugly as shit inside, too.

[purpletele]

> i am too danm old to use a touch screen.

BlueTooth keyboard.

I got a $50 Logitech and a $13 no-name. Both beat piss out of fat fingers on glass.

https://www.logitech.com/en-us/product/multi-device-keyboard-k480 (huh, WalMart charged me full price)

https://www.amazon.com/gp/product/B00NOE7412/ref=oh_aui_search_detailpage (price dropped $2)

That is a great keyboard/tool!

[purpletele]

I am not a person to be relied on for amp building advice, but I'm guessing you have grounding issues.

The quietest and best amp I have built was a homebrew that relied on two grounding points, one for the preamp and one for the power amp. Works awesome. Ugly as shit inside, too.

Thanks, I am sure I had a couple of issues going on.  I am remodeling the layout now and I am going to build it back as Geezers Mini Bassman.

I am looking for nice smooth warm tone!

[Ledzepp007]

I am not a person to be relied on for amp building advice, but I'm guessing you have grounding issues.

The quietest and best amp I have built was a homebrew that relied on two grounding points, one for the preamp and one for the power amp. Works awesome. Ugly as shit inside, too.

Thanks, I am sure I had a couple of issues going on.  I am remodeling the layout now and I am going to build it back as Geezers Mini Bassman.

I am looking for nice smooth warm tone!

Sounds cool.

I actually think you had a really cool idea to begin with.

[purpletele]

I decided to do a little MOD to the Wrecked Bassman.

I have everything I need to revert this to The Mini Bassman.  I had to give myself some room to work neatly.

Should be pretty smooth from here.

[purpletele]

Update:  Geezers Mini-Bassman

The reconstruction project was much more enjoyable from a work space standpoint.  I understand the need for really short wires on a high gain monster, but I really wanted to hear and feel the Mini Bassman circuit.

I had a few minor tweaks at start up and then the amp started to develop its tone.  This amp is the quietest to date, it is really pleasant to have low noise.  No issues so far.

I am going to play it for a few days and see where it goes. 

This amp is really loud, I bet its overall rating is in the 12 -15 Watt Range. 

My first impressions are that I like the feel of the Power Tubes, but it might be a little dark. 




Mini Bassman Voltages                  
4.26.17                  
                  
                  
V1-1   147   V      V3-1   48   V
V1-2   0   V      V3-2   24   V
V1-3   1.42   V      V3-3   53   mV
V1-4   0   VDC      V3-4   0   VDC
V1-5   0   VDC      V3-5   0   VDC
V1-6   147   V      V3-6   279   V
V1-7   0   V      V3-7   274   V
V1-8   1.42   V      V3-8   70.2   V
V1-9   0   VDC      V3-9   213.2   V
                  
V2-1   135   V      V4-1   45   V
V2-2   14   mV      V4-2   24   V
V2-3   1.6   V      V4-3   8.7   mV
V2-4   0   VDC      V4-4   0   V
V2-5   0   VDC      V4-5   0   V
V2-6   267   V      V4-6   279   V
V2-7   135   V      V4-7   288   V
V2-8   138   V      V4-8   70.3   V
V2-9   0   VDC      V4-9   203   V

[purpletele]

Voicing Update & Questions

The mini-bassman has some serious meat on the bone.  I have a few questions that I am sure are easily answered.

1. This amp is quite powerful and in order to get full tilt boogie it needs to be cranked, which I can do when I hook it up to my Fryette Power Station (Great Tool).  I seem to be a big proponent of the PPIMV.

a. If I cut in a PPIMV I need to remove the two 220K resistors and replace with a 250K or 500K Audio Dual Pot with 2.2 M resistors in line?

b. What is the Level Control that Dr. Z is using on the Cure and is that something I can try here.

2. The tone is really nice however it is a little dark.  I know it may get a little darker with the PPIMV.

a. Without the PPIMV do I change the value of the 47 pF Cap splitting the 82K resistors in the power section to something higher such as 100 pF to shed the minor blanket, or do I drop a silver mica cap across the Master Pot?

b. If I cut in the PPIMV do I add two  bright caps the dual pot?

3. Does anyone have any suggestions for Mods that I can try for fun?   This is a perfect platform for experimenting. 

Thanks for any input as always!

BV