Mk IIb BIAS Mod or not?

[Harry the Horder]

I'm about to recap my mkIIb and am wondering if at the same time I should perform the Variable Bias mod. Fitting a 50k linear cermet pot. Any pictures of this mod? But most important Is it worth doing?
Any other mods worth doing?

 

[trem]

I'm no expert, but if your amp is not simul-class, if I were you I would definitely have it modded for adjustable bias. There's also an effects loop mod for IIB which supposedly makes a huge difference in sound. I'm not sure about the details. Do a search using the google function, don't bother with the standard search tool.

~trem

 

[Harry the Horder]

OK techy's my bits have arrived to recap the Amp.
before I do the Variable BIAS mod I want to check I'm doing it right.
From what I see I remove the 6.8k resistor and fit in a 1.8 or near plus a 50k lin cermet Pot.is that right?and can I use a Carbon comp resistor for this as it is DC ? I ask because I understand DC eats Carbon element Pots so is a Carbon comp resistor OK in there? Any Pictures of this Mod?

 

[stokes]

Looking at the IIB schem I have,it shows a 6.8k in parallel with a 10k.I would just replace the 10k with the 50k cermet pot,leave the 6.8k in place.Set the 50k pot to read about 10k or whatever the value you are replacing,before installing,then you can adjust from there.

 

[Harry the Horder]

Thanks Stokes I'll give it a shot.

 

[Harry the Horder]

OK next question.
Whilst checking out the circuit for the mod I might have to reroute some of the rsistors to get my Cermet pot in safely.I know the values of these resistors but what composite are they ? They look to me like ceramic resistors but painted brown to look like carbon comp. so which should I use as replacements? That's my last question honest! I suppose you'll be wanting Photo's next ! Thanks in advance.

 

[Harry the Horder]

OK ,well I've done all the re-cap job and want to finish of with the BIAS Mod. I know what resistor to remove ( the 10k by edge of board ) The question is once I have removed the resistor how or what pins do I use when fitting the Cermet Pot??? Am I right in assuming one goes down to earth and the other two remaining take the place of the 10K resistor? I 'd sooner ask first then do the mod it's better than watching your pride and joy go up in smoke!! Do I need to put another resistor in series with the lead going down to earth or is the fact of the 6.8k in parallel good enough

 

[nomad100hd]

i'd use metal film resistors carbon comps drift value with heat and higher voltage.

 

[stokes]

OK ,well I've done all the re-cap job and want to finish of with the BIAS Mod. I know what resistor to remove ( the 10k by edge of board ) The question is once I have removed the resistor how or what pins do I use when fitting the Cermet Pot??? Am I right in assuming one goes down to earth and the other two remaining take the place of the 10K resistor? I 'd sooner ask first then do the mod it's better than watching your pride and joy go up in smoke!! Do I need to put another resistor in series with the lead going down to earth or is the fact of the 6.8k in parallel good enough

Harry,to wire the pot,one leg gets connected to the "wiper leg" and connects to one side of the remaining 6.8k and the remaining leg or the pot gets connected to the other side of the 6.8k.Your pot is now a variable resistor where the 10k used to be.