Looking for gut shots of mkIIB RP-9C circuit board

[Jamme1961]

Trying to get my amp back to stk form need pics to verify my amp thanks for any help

 

[Less02]

Here is mine. There is a obvious repair for the heater trace. That a very late MKIIB XHRG

 

[Jamme1961]

Thank you - do you know the value of the cathode cap on v3b ? I’m pretty sure it’s 22uf but just confirming- again thanks for the pic

 

[Less02]

Mine is a 0.47uf

 

[Jamme1961]

Thanks so much- mine is 22uf i think way to much bass - Mesa is all over the place with this stuff

 

[Less02]

There is a lot of version and mod, and only one schematic available, which is in most case innacurate.

 

[edge59AlnicoIV]

Thanks so much- mine is 22uf i think way to much bass - Mesa is all over the place with this stuff

Guess I was not too far off was I? I don't know why people don't believe what I post even after all the effort and pics, schematics I shared.

 

[edge59AlnicoIV]

Trying to get my amp back to stk form need pics to verify my amp thanks for any help

If this guy's shot does not back up what I said, I give upit's pretty obvious the cap is not a 22uf in his amp, it's a .47uf, like I said .22-2.2, where his has the .47 (thank you Less02 for sharing, it's a clear pic too) most likely as Mesa was changing values along the way, I have seen variations of the IIC+, look at all the Mark III stripe revisions, subject to change without notice, to build a better beast as time goes on. I have shared more than Mesa would have shared, God knows I have seen many Boogies, Marshalls, Dumbles, Fenders etc. In over 50 years of doing this, you might think I might know something about these amps...

 

[Jamme1961]

Guess I was not too far off was I? I don't know why people don't believe what I post even after all the effort and pics, schematics I shared.

It’s not that - it’s all the different values out there - from Mesa - I believe you - look at my amp 22uf this amp is .47 both the same circuit board two way different values. It’s good to get this information. Thanks very much for all you help on this - hope you’re not mad at me?

 

[edge59AlnicoIV]

If this guy's shot does not back up what I said, I give upit's pretty obvious the cap is not a 22uf in his amp, it's a .47uf, like I said .22-2.2 most likely as Mesa was changing values along the way, I have seen variations of the IIC+, look at all the Mark III stripe revisions, subject to change without notice, to build a better beast as time goes on. I have shared more than Mesa would have shared, God knows I have seen many Boogies, Marshalls, Dumbles, Fenders etc. In over 50 years of doing this, you might think I might know something about these amps...

It’s not that - it’s all the different values out there - from Mesa - I believe you - look at my amp 22uf this amp is .47 both the same circuit board two way different values. It’s good to get this information. Thanks very much for all you help on this - hope you’re not mad at me?

That is what I trying to explain, thankfully Less02 had some clear un modified but different than 22uf pics to back it up, maybe try a .47uf there. Like I was saying Mesa was constantly changing values till the got something that stuck, even then when the Mark III's came out, the were always changing values with all the different colored stripes, but went back to the IIC+ version, and even still would have a part here and there be different. Sometimes due to vacuum tubes that were available and how they interacted with the circuits, they would change a value to get a result they were after reading the o-scopes. Not mad at all just trying to help.

 

[edge59AlnicoIV]

That is what I trying to explain, thankfully Less02 had some clear un modified but different than 22uf pics to back it up, maybe try a .47uf there. Like I was saying Mesa was constantly changing values till the got something that stuck, even then when the Mark III's came out, the were always changing values with all the different colored stripes, but went back to the IIC+ version, and even still would have a part here and there be different. Sometimes due to vacuum tubes that were available and how they interacted with the circuits, they would change a value to get a result they were after reading the o-scopes. Not mad at all just trying to help.

I think now you need someone to verify the wiring on V4. I have been in your spot many times before, seeing something that does not add up, sometimes you to see it from another angle with schematics, others pics and input from others or you will be stumped for days and confused. Maybe someone like Less02 might be able to walk you through those cap/resistor values to help sort out the circuit for you since he has been so kind as to upload some good clear pics

 

[Jamme1961]

It’s great to get pics and values- I’m going to get as much information as I can and post here for people to use. I was on this forum years ago been away for awhile-

 

[Less02]

Some boards might have error on them too, where QC didn’t catch. This was all manual at the time.

 

[Jamme1961]

was just messing with the .47uf value. that seems to be a great match, everything works together nicely - im not fighting to much bass on the lead drive but not enough bass on the clean - the pull bright on the lead master sounds great too. Going to play it now for a couple of days- see how it goes. Thanks again to you guys- for sticking with me on this stuff.

 

[Less02]

Indeed, this amp always require adjustment when switching channel. It is more obvious with the reverb, it can’t be used at all onnthe lead channel. Bass setting also need to be increased on the clean channel as comoared to the lead channel. This is why the tone stack got separated on the mkiv. The mkii was still a prototype of an « incompleted » mkiv amp.

 

[Jamme1961]

Anyone know the value for the plate resistors on the preamp tubes? I’m looking at V1b and it’s at 330K instead of 100k ? It looks like it’s been changed, not factory. The rest of the plate resistors are 100k. Trying to verify correct value for RP-9C board.

 

[Less02]

Here it is