Need help w/ 2203 MV restoration/repair!! Tons of questions!

brandonl311 · Post by **brandonl311** » Tue Apr 05, 2005 1:24 am

I have a lot of questions, I'm restoring my modded 2203 Master Volume to normal specs. The amp in the picture is not mine, I found the pic somewhere, I can't remember where. I'm a bit confused on some of the resistor values, because on many diagrams I've seen, the resistors are different. I'm basically just double checking some of this stuff.

Ok guys, here's all my questions, coordinating to the numbers on the picture...

#1 - Ok, on each of those circles, there's a resistor (not the large power resistor) on pin #5 (I think, sorry lol) for each of the four power tubes that is connected to the circuit board from two different wires. Two of the tubes are connected to a green wire from the circuit board, and the other two from a faded red wire. What is the correct value for these resistors?

#2 - This resistor I'm not sure of the value, I think it's supposed to be 27k? But I think I seen different values on some diagrams I've seen.

#3 - My circuit board has this resistor, but on some 2203's, it's just bridged over with no resistor there? Which should mine be?

#4 - Both of these resistors I'm not sure what the value is supposed to be? Maybe 220k each?

#5 - This one is 56k on mine, which I'm pretty sure is right. But, you can tell the resistor here on the circuit board is not an original resistor. Once again, just double checking.

#6 - This resistor also doesn't look original. Not sure what the value is supposed to be at all.

#7 - Mine's 100k, pretty sure it's correct. Just double checking again.

#8 - On my tube socket, there's a larger looking cap placed over where the blue and yellow wires are. I haven't seen this on any other 2203's. Is there supposed to be a cap on this? Should I remove it.

Dax-The-Ax · Post by **Dax-The-Ax** » Tue Apr 05, 2005 2:39 am

#1 - I think these are 1.5K
#2 - 27K is correct
#3 - This is a 2 Watt 10K - two yields more gain, one will have less. Either is OK.
#4 - These are 220K.
#5 - This is your slope resistor. 56K is stock. You can try 33K-More Dirt.
#6 - This is the V1A Cathode resistor. 820 Ohms
#7 - This is your feedback resistor. 100K More dirt. 47K is Stock
#8 - Not Sure, need a closeup. My 100 Watter had it, though.

My fellow friends should double check my shit!!!

brandonl311 · Post by **brandonl311** » Tue Apr 05, 2005 5:13 am

For #1, on schematics, it appears as if they would are 5.6k resistors on pin 5. As you said, 1.5k, is whats on mine at the moment. But all of these resistors definately don't look stock, so that's why I'm skeptical. On some of the 2203 pics I've been looking at, I don't even see these resistors there at all.

Billy Batz · Post by **Billy Batz** » Tue Apr 05, 2005 8:33 am

It doesnt matter. Both 5.6k and 1.5k are common. Those are grid resistors (or 'swamp' resistors) and really theyre only bandaids to help with noise (PO). You only want to go as high as you need to. So if your amp is stable with 1.5k then your good to go.

As far as the #2 resistor, thats the bias range resistor.

Like Dax said #3 is a 10k. They went back and forth a lot. Its a decoupling resistor thats part of the power supply. Its effect is extremely subtle but having 2 10ks in series like yours drops the voltage to the preamp which does give it a more saturated sound.

If you say #5 looks swapped out it probably was. 33k is stock in 2203/4s. Marshall used 56k only in the early JTM circuit amps and in the Super Bass models.

That #6 resistor paired with the .68 film cap is actually 2.7k. There is no 820 ohm resistor on the V1 cathode in 2203/4s. If its not original theres no telling what it could be but you can look at the color code.

#7 NFB resistor. 100k is stock. 47k is a Super Lead value and will increase NFB for a cleaner, less hairy more ringing grinding gain. 100k blocks more NFB by a long shot and it sounds a bit hairy and dirty. Its a subjective call. I like the early 27k in my 100W but for a 2203/4 100k may be best.

#8 yes that should be there. Thats a screen-grid resistor (not cap) and it should be 1K/5W. They sometimes look like white ceramic blocks.

Flames1950 · Post by **Flames1950** » Tue Apr 05, 2005 12:07 pm

For #3, by the time period of that circuit board Marshall used two 10K's for the 100 watt amps and only one for the 50 watt amps. Earlier 50 watters got both because the overall plate voltages were higher and it took two to get the voltages in range on both the 100's and 50's.
That one looks to be what, about a '78 to '81-ish 2203?

brandonl311 · Post by **brandonl311** » Tue Apr 05, 2005 1:48 pm

My #8 doesn't look like a ceramic resistor at all. It looks more like a smaller version of an Orange Sprague drop. Except it's dark brown. The writing on it appears as so....

.001-2000V
PVC 2x21-10%
Mallory

Flames1950 · Post by **Flames1950** » Tue Apr 05, 2005 2:31 pm

brandonl311 wrote:My #8 doesn't look like a ceramic resistor at all. It looks more like a smaller version of an Orange Sprague drop. Except it's dark brown. The writing on it appears as so....

.001-2000V
PVC 2x21-10%
Mallory

Some later MV's got a cap like that (is it between pins 1 and 3?) to help suppress parasitic oscillations. I thought yours looked earlier than that but I don't know exactly when they started appearing. You usually find it on the JCM800 schematics from around '88. I didn't think it was on the earlier JCM800 schematics or the JMP schematics. Again, I'm guessing at the year of your amp when I say these things ('78 to '81.) Looks like the JMP faceplate at least. So it may have been added to squelch problems from the different mods or something.

brandonl311 · Post by **brandonl311** » Tue Apr 05, 2005 2:56 pm

Sorry I didn't make it a little clearer in my first post. The amp in the photo is not mine, it's just a pic I found of one that is similar to mine.

brandonl311 · Post by **brandonl311** » Tue Apr 05, 2005 2:57 pm

...Also, mine is a JMP 2203 (1980)

Billy Batz · Post by **Billy Batz** » Tue Apr 05, 2005 5:23 pm

brandonl311 wrote:Sorry I didn't make it a little clearer in my first post. The amp in the photo is not mine, it's just a pic I found of one that is similar to mine.

Ahhhhh......

Dax · Post by **Dax** » Tue Apr 05, 2005 7:32 pm

I was Close!

brandonl311 · Post by **brandonl311** » Tue Apr 05, 2005 10:06 pm

Thank you so much for all your help guys! I appreciate it a lot.