18 Watt with Chiefton Power Section Complete, going further

[Ed_Chambley]

I am going to make another one of these.  This time in a much larger chassis and all new good quality parts.  It is a cool amp for heavy rock.  Very brown sounding.  I have a couple of questions.  I had a problem with parasitic oscillation in the original which was fixed by adding shielded cable from the inputs to V-1 and from the board to the Master and Volume and the treble.  This one is going into a 17 x 10 x 3 chassis so I will have the room to run the wires neat and correct.

The question I have is the use of the shielding cable in the tone stack.  I have the wire connected to the board and the shield grounded at the back of the pots.  If I were to use shielded cable in the entire tonestack, can or should you use them between pots and if so, which end would ground, either?

The other question I have is about the tonestack in the TMB.  It doesn't seem to have very much bottom.  As a matter of fact, there is not a lot of change in any of the tone controls.  There is some.  To move it towards mid scooped like a Blackface fender, or this just the nature of an 18 watt?  All of my Marshall are similar, but not as restrictive as this.  I put an eq in front of it last night and it is very capable of a tight, deep bottom.

I changed the choke to a 3 henry from the 20 henry and added a 1k5 10 watt dropping resistor between C1 and 2 and it opened up and became increasingly more touch sensitive.  I still have the choke from C2.  I am also wondering about the filter cap values.  It has a dual 50/50uf-500v (C1 and 2), 22uf-C3 and 22uf-C4.  I know the filter caps remove ripple, but I have also read where larger values tighten up bottom end.  If it does, I certainly do not understand how or if this could benefit.

The amp roars, but it is almost impossible to get a clean sound out of the TMB channel without losing volume.  The additional gain stage is really hot which is cool, but is there a way to tame it and make it so a footswitch can go from clean to mean?

[Ed_Chambley]

dim light bulb moment.  

I have not heard of the chiefton power section.  Did an Internet search no luck.

Do you have a schematic?

It is a matchless Chiefton.  Here is the link to where everyone helped me make this thing work.  It is a looooooooong thread.

http://www.el34world.com/Forum/index.php?topic=13598.0

[Ed_Chambley]

Now I understand.   Its a matchless Chieftain,   I know better than to knock somebody's spelling, because, if I could spell, then I likely would be a better engineer or better enginer.   
   (Side note, in 1976, New Mexico Tech issued there Mining Engineering degrees with a misspelling, "Mining Enginering", Seven people got the misprint.)

found a schematic for the chieftain,

Thanks for posting

Just curious, Did you install the optional cap in the preamp stage? 

No I did not.  It is a straight 18 watt tmb (the ritchie layout) preamp.  It changes at the PI to the Chieftan.  It has separate caps bypassed by 270 ohm resistors with a common ground. To pin 4 it has 1k 10 watt feeding 2 others of the same and then connects to pin 4.  From the 220k to a 5k6 resistors to pin 5.  I have 396 to the plates and 378 to pin 4.  I plan to draw it out, but just have not had the time.  I have the files to basically copy and paste for schematic.  What I am wondering is if a plexi pre might be better.  Don't get me wrong, the amp sounds fantastic as it was just an idea I had that worked well.  It seems tweaking the 18 watt TMB is difficult as there is a lot of gain to deal with.  I like the gain, but it's a one trick pony on the TMB input, the normal channel has a very nice compressed clean tone.
I am just thinking out loud and looking for those who have tweaked a 18 watt TMB.  To be able to add and remove the extra gain stage would be a great feature as in the new build I plan a Reverb and a Bluesbeaker Tremolo.