marshall 100 watt major build having issues

[marshall]

Hello , new to this site , heard this is the place to be to get real answers to some issues I'm having with a build i had done .  first off its 100 watt ultralinear  marshall type  /kt88 build .  output transformer by merren audio and  prw tranny by hammond 278cx.  have mustard caps , iska resitors , all good high end  product in this build   .. what im hearing when i strum a note , i hear a  faint fuzziness to it at the end , even  clean or dirty sounding  mode .... replaced tubes ,  patch cords, tried different wall circuit.   the builder  went over all   parameter values  on components ,   guiar is going straight into the amp    any insight ?       jeff

[Ritchie200]

Jeff,

First, welcome to the forum!  Second...oooooooooh!  I wanna see porn of your build!  Welcome to the dark side!

Third, we need more info.  Schematic?  Pics?  Need to see layout.  Just to verify, you replaced all the tubes, not just move them around?  Is this a true copy of the Major? If so, what are you using for your driver tube?  Does this happen at all diferent volumes?  Is the ghost note true to the original or does it sound dissonant?  Did you try a different guitar?  Easy stuff first.

Jim

[marshall]

noticing as well when i uplug from high channel to go to low channel   the amp makes a distorted noise untill you stum the guitar then it  begins to sound better . I will post some closup  gut shot pics ltr tonight

[darkbluemurder]

I am not sure whether you copied the Major exactly but one thing that has struck me as odd with this amplifier is that it has an ultralinear output stage AND global negative feedback. Moreover, the feedback not only includes more stages than usual but also is put back into the circuit before the tone controls. This means that when you change the tone control settings you change how the feedback works. This to me is a potential source of instability.


Have you tried to disconnect the global negative feedback? If yes, does the problem persist?


Cheers Stephan

[MFowler]

Sounds like there is a missed solder joint/poor ground.


Mark

[Ritchie200]

darkblue


Actually what happens with that arrangement is the tone controls do not have much affect as compared to “traditional” Marshall amps. However I think it contributes to the unique tone. The only thing you have to worry about with the original design are the screen resistors as the original were not big enough for the voltages they were running. As a result tubes did not last long if you were running at any decent volumes. That’s why I was wondering how close their design was to the original. Original runs 620v on the plates. The other issue was the crappy OP tranny as they were junk. That would not be an issue here. The amp has a lot of bad press but would run fine with a few upgrades.


Jim

[marshall]

tried to post pics but keeps telling me file to big   as for the particulars on it  , your questions will be answered  when i can post pics  .  i had a friend of mine who  owned majors , done some of his own  work on them  , not a teck but knows his stuff on majors .  there is a few videos on youtube of his head    68 marshall major   r/t mods .    hoping he would chime in on here to help out with some of the  teck questions . I had this amp built by a tube amp  teck in ajax , ontario     .   there were a few  issues from  the  original build    but had mike  r/t  clean those up . but the note distotion  still  exist after  mike spent quite some time on it   trying to track it down.    would faulty filter cap   cause it , i know    fault filter caps   will give you  hum ,     im thinking something in the pre amp circut  , freq issue    . merren wound i o/t  for 4000 ohms  ,  any  ideas on this area ? . is it possible that there is not enough filtering in powr supply ?
   

[Ritchie200]

Mike RT knows his stuff when it comes to Majors.  Did he just throw up his hands?  Again, I (we) need to know more about the design that was used for this build before taking a stab.


Jim

[jojokeo]

darkblue
The amp has a lot of bad press but would run fine with a few upgrades.

Deservedly so if the amp is a POS without special mods/upgrades after leaving the factory! If a Ferrari came out of the factory breaking down without the necessary "upgrades" to keep it on the road/track - you'd say the same thing here too.

[jojokeo]

would faulty filter cap   cause it , i know    fault filter caps   will give you  hum ,     im thinking something in the pre amp circut  , freq issue    . merren wound i o/t  for 4000 ohms  ,  any  ideas on this area ? . is it possible that there is not enough filtering in powr supply ?

Of course it would have an affect, but there's too many things to discuss without a schematic and/or couple of chassis & gutshots to see exactly the way it sits. Especially if it was built by someone else (not factory)! I've seen crazy stupid easy mistakes by a lot of guys that think they know enough...but don't realize their own shortcomings and many many things that they think they do. Some even on this forum  - believe it!

[Ritchie200]

darkblue
The amp has a lot of bad press but would run fine with a few upgrades.

Deservedly so if the amp is a POS without special mods/upgrades after leaving the factory! If a Ferrari came out of the factory breaking down without the necessary "upgrades" to keep it on the road/track - you'd say the same thing here too.

Oh please...  Coming from a guy who sits on a stool with reading glasses and a music stand when he plays out, you are the equivalent of James Lipton on stage - hardly qualified to critique the pinnacle of ampaliscious rock and roll goodness that is a mans man amp from the man on the silver mountain man in black, man!  So go sit in the corner and play with your little tubie girlie man amps and leave this discussion to the men of the house.

Jim

PS have you started building my amp yet?

[silverfox]

Personally I'm not really that impressed with the Major. It is impracticle. Sorry. To each their own... However, in the interest of advancing diversity, here is my contribution.

[jojokeo]

Was Lipton (it was George Plimpton?) that journalism guy that also thought he was an athlete and played QB for the Bears or Colts for a play or two way back when we were kids? You told me your favorite was about that lion cub called Born Free and how it was so touching & emotional you always cried at the end. 😭


Are you referring to the amp sluckey is building? The one that’ll have more than  twice the output power over the one that you are wanting? Guys scaling down from 200w to 2w shouldn’t be throwing stones? 😆


When are you going to pick up your favorite guitar that got captured in the photo? I got it holding together but don’t know how many more of your air guitar tantrums it can take with you trying to recreate the Cal Jam festival in your bedroom on that beat up beta VCR recorder over and over?! Did you get your garage set back up yet to play your summer gigs for the neighbors again this year?

[Ritchie200]

Different amp, a very different amp.  Also a lot of incorrect information.  The 200 was designed by Marshall.  The 1967 was designed by GEC.  Nobody but Mick Ronson wanted the 200 with the active tone controls.  They were also very unreliable.  Marshall then tried several versions of a typical Super Lead style 200 watt with KT88s and could not make them last.  They even tried a 6 gun EL34 amp.  The transformers were not up for the task.  They were in a wattage race and finally went to GEC asking for help.  GEC went with what they knew, a classic Williamson cathodyne, UL, HiFi style amp.  Unfortunately this design was not meant to be overdriven and there were problems as I mentioned above.  Given the fact that Ritchie used the same 6 heads from around 1968 to 1993 I think says a lot - including the one blown up at the California Jam and thrown off the stage (only one broken tube).

Yes, they are very impractical in this day and age.  But like many special things, nothing else sounds like they do.

Jim

[marshall]

mike r/t major took all mods out   , ppimv/ cascading ,and tested it again     same issue as posted . I measured the b+    590 volts dc in the 110 volt tap  mode   and540v dc in 125volt top mode  . bias set to -41 ma 

[marshall]

&feature=share




this is the video of the mini major in action

[marshall]

some gut shots in this video , plate voltages that mike mentioned in video were not accurate based on what information i got from   moratto   the builder of the amp .  I had a falling out with him based on this build  and the  many issues it had when i picked it up   as a finished working tube amp.

[VMS]

You can scale down the size of your picture so it's under 1M and then post it here.


Also temporary passive loop before PI would be great, then you could feed the preamp to another amp and try the power section with other preamp. That would help determine if the issue is with preamp or the poweramp.


Schematic and layout would be nice to see too

[jojokeo]

  .. what im hearing when i strum a note , i hear a  faint fuzziness to it at the end , even  clean or dirty sounding  mode .... replaced tubes ,  patch cords, tried different wall circuit.   the builder  went over all   parameter values  on components ,   guiar is going straight into the amp    any insight ?       jeff

Apologize Marshall, Ritchie & I have fun between the seriousness & info and problematic issues can be very frustrating indeed. I believe what you are experiencing is classic parasitic oscillation. Parasitic oscillation can take on many forms like sounding like a cabinet buzzing or a mosquito along for a ride on the note and others. It is many times frequency specific (occurring on a certain fret or frets) but not always. It can also negatively affect sustain as it can be out of the audible hearing range. This usually is an issue with higher gain amplifiers and caused by one of several possible issues being component placements, lead dress, poor grounding/ground loops, lack of shielded wiring on sensitive (high Z low level near low Z high level) wiring, etc.

In looking at your first video it appears that your input wiring and the wires going to & from the PPIMV are not shielded? This is the first thing you should correct is wiring these with shielded wires - especially the PPIMV as I've had/seen numerous issues here when not shielded. Same thing for any signal wire crossing over, under, or near other parts of your circuit as mentioned earlier.

Important: do only one thing at a time:

1) Start with your input wires going under the board. (This is rule #1 always to try to do this when it is not short and goes anywhere near other wiring)
2) Change PPIMV wiring for shielded wire (the way most everyone/manufacturers does their layout for the pi is always backwards and not correct how it should be done IMHO)
3) If you have Send/Return - shield these wires also (just general good practice like input wiring above)

jojo

If the things above do not change anything for the better then don't worry, there's more to consider - it's first things first here.
I had no time to watch entire video, pictures can sometimes be better than videos since there's no moving around and higher resolution can be obtained. If you have jpeg or other photo style types, simply open Paint program and then re-size accordingly and re-save file using "save as". It will create another re-sized file and not affect original high resolution file. Do not re-size too low...

[MFowler]

Easy way to resize photos if you can figure out how to do it with photo editor is to upload to your facebook or other online sources it automatically resizes the photo and then save that to your smart phone or PC to upload on this forum.


Smarter people can further advise you.  When I changed to Windows 10 I can't figure out how to resize a photo.


Mark

[Ritchie200]

Maybe it's the angle of the video but I don't see any grid leak/reference resistors on the input jacks - usually 1 meg.  Could the absence of these introduce enough noise into a high gain circuit to cause what he is experiencing?

Jim

[marshall]

https://www.guitarscanada.com/index.php?attachments/b8b938ca-e5ba-4326-888e-9553f81ca83a-jpeg.168737/

[marshall]

https://www.guitarscanada.com/index.php?attachments/8468cac1-3a92-4bd4-8595-949b32674493-jpeg.168793/

[marshall]

https://www.guitarscanada.com/index.php?attachments/8468cac1-3a92-4bd4-8595-949b32674493-jpeg.168793/

[marshall]

https://www.facebook.com/photo.php?fbid=10212664605862918&set=a.1810176087030.162179.1018811034&type=3

[marshall]

https://www.facebook.com/photo.php?fbid=10212664605942920&set=a.1810176087030.162179.1018811034&type=3

[marshall]

https://www.facebook.com/photo.php?fbid=10212664605902919&set=a.1810176087030.162179.1018811034&type=3

[jojokeo]

Marshall - the pictures still show to follow my steps listed. You have no signal carrying wiring shielded, protected, and isolated.

[marshall]

havent done any  cleanup of wiring yet , updates next week

[marshall]

http://www.jj-electronic.com/images/stories/product/power_tubes/pdf/kt88.pdf

[jojokeo]

hello again , took my amp to martin newal from total tone  in oshawa ontario  today . checked out the amp anf found single stand of wire  that was not included in the solder joint touching another component   ,also found 6  bogus cold solder joint problems  , no issues now    working like it should  , no hum no hiss no most of sll no  note fizz. many thanks for all input on  the forum.    I completly forgot to rebais the amp  ,    being ultra linear  does the bias  differ    ,,,, running teslovak  modern kt88’s(jj,s)   590 vdc plate voltage .    what dhould i bias at ? 41 mv ?

Normally 590Vdc class AB is 32.6, and 41 would be for high AB.

[marshall]

great thnx   i set it at -32 mv   .   I was wondering about changing out the modern  resistors used in this build to nos Iskra   . and changing the  current modern suntan  .047uf  630 volt coupling caps  with 600v astron .    doing all of this will i notice a difference in tone ?

[sluckey]

Absolutely. It will sound much richer.

[marshall]

finding the 32 mv bias setting  a little stiff sounding  . wondering if its a cold bias level reading online  about ultralinear  biasing   and I am getting mixed  opinions on the REAL bias  parameters   .most  post I’m reading  are saying  to set bias at 42/50 mv .   Just to clarify  my  setup /////The    O/T   is a custom wind  merren audio   with a 4k primary impedence  ,   measured plate current is 590/600 volts  when amp is on , moderm kt88’s teslovak  which is made in same factory as the jjkt88   plz  lmk  correct formula or a brief understanding on  how to calculate it correctly .   regards   jeff

[jojokeo]

Raise to 40 and try it out. If more to your liking then leave it. Don’t get hung up on an exact volt/mA or two as long as you’re happy an tubes not red plating you’re fine.

[Ritchie200]

+1  I get it close on my major and the rest is by ear - watching the tubes.

Jim

[marshall]

hello again   . still having same issue with the note fizz  that I thought was fixed but its still there .tried  changing tubes, cables , guitars ,cabs. I have  added more nos iskra  resistors to replace  other current ones to make it more nos sounding .Is it possible that  there is an issue with    ppimv/ wrong  values  in the circut somewhere, not enough filtering . input wires were shielded , tried shielding   the 3 wires  on the ppimv  together  but got some nasty  static and loss of output . I resoldered  all joints .  when i turned the ppimv up past halfway  the fizz seems to  subside. which leads me to think its an issue though the ppimv at low to moderate levels .    Is there another are in the circut that the ppimv  can be wired   to solve the issue .I had also tried  maxing out ppimv and turning  the volume down on the guitar , seems to  be less fizz . but you loose top end  when dialing your volume down   .    Is it a possible phase issue .     

[marshall]

Maybe it's the angle of the video but I don't see any grid leak/reference resistors on the input jacks - usually 1 meg.  Could the absence of these introduce enough noise into a high gain circuit to cause what he is experiencing?

Jim

they are at the very btm  , but only on one set of input jacks not on other set

[marshall]

both are on now   but same issue

[jojokeo]

tried shielding   the 3 wires  on the ppimv  together  but got some nasty  static and loss of output . I resoldered  all joints .  when i turned the ppimv up past halfway  the fizz seems to  subside. which leads me to think its an issue though the ppimv at low to moderate levels .    Is there another are in the circut that the ppimv  can be wired 

Something is wrong by saying "tried shielding   the 3 wires  on the ppimv" - This is a dual pot yes? There are SIX wires to be soldered if it is a LARMAR type?
Also you're not saying how you're using it? If you are turning it down like you are saying then you must be turning up your preamp? This will induce distortion from your preamp. By saying "fizz" things start to become ambiguous without being there and operating and listening to what's going on. But it seems that you have mis-wired your ppimv control!? You should definitely not have nasty static and loss of power. You must re-look at what you've done and get this corrected before moving forward. This could still be your issue?

Also, I thought you also have a send & return jacks? Shield these wires going in and out to the circuit also.

Confirm that you are not soldering both ends of the shielded wire grounds thereby creating ground loops?

[marshall]

tried all of those ideas , still same issue   . the fiter caps in the pwr tranny   are jj 450 volt , 350uf in series .    one side of the series set have 120 volts input , other end has a short grnd and return wire to hammond 278cx .    there are no resistors on them  , are they needed  ? is that enough capacitance   to keep the hammond 278cx  smooth . i know when seriies two  capacitors of same values   you will get half its rating  in “uf” but combined total voltage handling . would changing cathode  res/cap values help . currentally it has 2.7k iskra  220uf  rifa  40 volt ,

[jojokeo]

Again - it still doesn't seem like you have the MV control wired correctly? And you haven't provided any updated photos, layout drawing, or schematic of what you're doing. Look at your wiring job (going by the only pics you've posted) and look at mine. Your output wires are right next to the sensitive signal wires. Have you corrected any of this yet?

[marshall]

is your amp ultralinear   major design .  would love to see a  drawn schematic on that ppimv .   terminating   right on the tubes with resistors   , never seen that  one before . as for my issue  , all mods(ppimv, cascading) were removed from circut   and still have the  distortion . I read about  blocking distortion , very close to my amp issue  . I will try to get schematic drawn  of my amp , also got a 100 watt schematic of a major   100 watter  will post it shortly .

[jojokeo]

No, it was a custom design I made for someone but the ppimv is the same as any using fixed bias. Blocking distortion can be fixed easily using voltage dividers and/or high value grid resistors. Grid resistors should have short lead lengths soldered directly to the socket pins like seen in the photo. I have them shrink wrapped. Here's a schematic if it helps? Also, importantly - what value of dual pot are you using???

[marshall]

250k with 100k failsafe resistors.

[jojokeo]

The "failsafe" resistors should be 2.2 Meg so that they don't affect the pot's value or taper. You have made a parallel resistance of 71.4k on both now as it's turned. If it were me I'd remove them entirely, they're not needed. They are only for "protection". In the future when/if things get fixed, then put the correct ones on (and once the wiring is done properly).

[marshall]

tried  the 2.2 meg in the failsafe position on the ppimv , didnt do any thing to the sound  but got a super high frequency  fizz  sound when 3/4 gain on ppimv ..bit with the  current resistors there was a better response  in volume when increased ,  i will take them out  to eliminate any future  issues going foward to find and fix  my issue  . , as far as new found  issues . was informed that  my can cap values    are not  possibly the  correct  values ?,All are made by  JJ  ,I wanted the  f&t's  , but was informed  jj.s values  would work better in this build.    the major has  ////1-50 uf - 500v , 2-100uf- 500v and 2- 380uf- 500v ,  the 2- 380 uf-500v caps installed  in the  pwr section are wired series  for correct voltage  spec. tolerence of 600v b+.  but was informed there should be    1-5 watt 270 ohm resistor paralled across each cap    , what possible problems would this cause  with no resistors on the caps ?, also   I informed that the 2-380uf caps should be at a lower  value of  250uf  . thoughts ?