Russ said:
This post got a little long... grab your munchies and a drink
Hi,
I have a JMP Master Model 50watt MkII Lead (basically the 2204 before the model # when it had a long name and vertical inputs). I had just the sound you had described prior to your retubing. In my case, it was just a 12at7 in the PI position. It makes for a nice clean with massive bottom in low input. I also had dead 12ax7s in V1 and V2. I replaced the V1 and V2 with fresh tubes and took the 12at7 out and put it in the Mark IVa reverb. It changed the character all together. I put the 12at7 back in the PI and it was back. Maybe you had a 12at7 in your PI. Some people like that but as you noticed it can make your high input sound weak. I have a 1963 GE 12ax7 and 1960 RCA 12ax7 in it now with a balanced GT12ax7C/7025 tube in the PI. I just got some 1962 Blackburn Mullards in the mail so I am waiting to try them out. I have been a little busy lately or they would have been in there immediately. I want to devote a weekend to giving them a good listen. This will be my first set of Mullards. I might just use 1 in V1 and savor the flavor a little longer. I don't mind the GE or RCA in V2. The lifted resistors are known as a bright mod. It is done to take the squeally characteristic out of the amp. Some Marshalls like ours have a tendency to get ice-picky. This mod cures it. Marshall sounds best with a Humbucker, but they had to make it so Strat players could enjoy the amp also, thus they had to make it a little too bright. Listen to your amp with both a Strat and a Les Paul. You'll hear the difference immediately. There is no real volume adjustment inside for each channel except possibly a mod to change the voicing but then why have it? just go buy a channel switcher, a dual reverb, or a DSL. The 2204 really is a screamer though. Compared to a 2203 it is middier and gets up on power tube distortion sooner. The 2203 will sound a little deeper voiced if only for the headroom. I don't think you got modded for more gain. I think you were just accustomed to hearing your low so loud and prominent. If he reversed a bright mod then your amp is closer to stock. My JMP is every bit stock as the day it came off the production line minus 1 of the small caps on the underside of the pcb (no biggie), the cord was replaced in favor of the newer removeable type, and of course the tubes. The circuit has never been modded in anyway (just maintained- although they used an orange drop instead of a sprague). If you plug into your low input you will have to adjust your volume from the setting on the high input. The best thing to do is just remember where the two volume settings are. It is something we have to live with. The 2203 and 2204 are considered one-trick ponies for this reason. They do what they do well. Well enough to almost forget the low input or high input depending upon how you are using it. Plug into low and crank it and you have one of the closest plexi impersonations on earth. Plug into high and crank it and you have one of the most sought after distortions/tones ever created. Just get used to it being a single channel amp and you'll learn to live with it. I have come full circle with Marshall and found that I only need a 2204 (in my case a JMP version) or a post '87 2210 to get my Marshall fix. I still want a nice plexi though for when I get old and my hearing starts to go and I can really appreciate the loudness instead of getting hurt by it trying to achieve "the" tone. Before you go back in call and ask what your tech did exactly. Do not sound overly concerned but curious. Tell him you like the high input volume but would like to know why the low input is so low. He may very well tell you that it is just how the amp was designed. If your high input is overboard loud in comparison to the low as in on or off sounds the guy may have done a gain mod. Count your tubes in the back. Most guys will attack a gain mod by adding a tube to the circuit for overdrive (a cascading gain circuit). If there is only 3 12ax7s then it is not from an added tube. Take a look at the circuit and the schematics and see if any resistor values were changed. Also check to see if any were added or removed. The schematics are all over the place just do a search. If there has been any changes they will be really obvious. The board is really plain looking and there is a lot of space between the solder joints. Marshall soldering is immaculate also. Most techs are not as clean as the machines installing the components to the board. The pots and jacks will have been hand soldered but with a keen eye you can spot a resolder or change even by the color of the burnt flux. I have yet to see a tech that cleans up after soldering. On the other hand, I have also yet to see an amp built by Marshall that has original burnt flux on the solder joints still. You also might try changing V1 and V2. If your 12ax7 (dual triode) is stronger on one side it may make one channel (low or high) appear to be dominant. If I am not mistaken, both inputs share V1 (one on each half of the dual triode thus each having its own triode). I just got some Mesa tubes that had tested new on one half but were almost questionably bad on the other. It can get frustrating dealing with inconsistencies in new tube production or even your old used tube's wear. I found that my Mark IV eats one side of V2 and V3. I am not sure why either. If I were to study the circuit and experiment over the lives of several tubes I could probably figure it out but I don't have that much time to waste on it. I am fine just popping new tubes in when necessary. As far as the JMP goes, if it aint broke play it... and that is my philosophy with Marshalls. They either work or they don't. If you can't fix it with new preamp tubes, new fuses, or new cabling take it to a tech. If you start blowing fuses it is probably time for power tubes. Take it in anyway. As far as your current state I would just play it on high unless you really need to use the low input. As far as not taking it in for 5 yrs goes, that is foolish unless you just weren't playing it. If you were then you were lucky you hadn't had a more serious problem. I don't know of any power tube that would last 5 years of consistent playing. Preamp tubes tend to last twice as long as power tubes but can last up to 10,000 hours in the case of the 10M Mullards (I would like to see that claim in a guitar amp though. Guitar amps are hell on little preamp tubes.). You may have gotten some new caps as a reault of not having been serviced in a while. That may be what you are hearing as well. Sometimes a cap job will change the personality of an amp. Look at your transformers to see if the date on them coincides with the year of manufacture of your amp also. Sometimes a tranny change will affect your tone too. Oh here's a kicker.... check your impedance. A mismatched impedance will sound different also. I have heard of guys getting their head back and burning it up because they forgot to check the impedance. The techs had changed the settings to use their own cabs and well, the amps got fried by the complacent owners. You might also ask if the power tubes were replaced. If fuses start blowing it is usually time to replace the power tubes. Your tech may have biased the new ones a little hot to help get the more desired tone. You may have gotten accustomed to cold biased old dead tubes. This may be what you are hearing too. There are so many variables that could be the reason for the changes. It is true that your tech may have modded your amp too but usually they don't give away mods for free. Usually they charge you for them and are proud of their capacity. So unless you got charged for it, chances are it didn't get modded unless it was a gift from the amp fairy. Last I checked, there was no amp fairy...
My guess is that the freshening of your tubes plus maintenance and the reversal of the bright mod was enough to change your amp's personality enough that you are now experiencing what you had described. Usually the high input is a little louder than the low anyway.
Let me start by thanking you, Russ.
I realize that I may have grown accustomed to the way the amp sounded with the old tubes. However, before and after the work there was a difference in volume on one input that is much more than it should be. One one input (high prior to work, low after) the amp at full volume/gain is quieter than my 15 watt peavy practice amp set on 2.
The amp hasn't had full use over the five years, maybe 2 years of 4 times a week for 2 hours.
I spoke to the tech and he only replaced the preamp tubes and a resistor. There are no more tubes than before, 3 12Ax7's and 2 EL34's. I haven't opened it up fully yet, but I will check for the things you metioned once I have the time and a schematic.
I do need this amp to operate with both a "clean" and dirty channel due to the music I'll be playing.
If these are truly one trick ponies, i may have to go another route, although I cannot afford to shell out another grand on a head at this time.
When I spoke to the tech, he suggested buying an EQ or boost pedal to put between my AB switch and the low input, to adjust the level between channels.
I figure I may as well go back to the way I was using it: a distortion pedal into the low input to go between clean & dirty.
In that case, though, I would need the amp to go back to the way it was as the low input is
significantly lower than the high, not just a little bit.
He said he'd have to charge me to open it back up. I reminded him that he said his work was guaranteed. He then suggested that, if I was comfortable, to replace the power tubes myself. I'm thinking he may have made this suggestion as it would void he guarantee since I worked on the amp.
What's more is that I'm disappointed that he quoted me $60 labor to change all 5 tubes, then only replaced to 2 preamp tubes and still charged me the $60, plus $20 for the resistor/soldering.
I fear that my ignorance is costing me money. I wish that the tech would explain things as they truly are, but i feel that he is basically acting like an auto mechanic since my ignorance benefits his wallet. I realize that this is how lessons are learned and I want to learn as much as I can.
Once again, any and all input is appreciated. I'll do some more research and updat soon.
Thanks
