amps works but one problem

jj jafar · Post by **jj jafar** » Sat Jan 29, 2005 6:55 pm

well i got my mv board and ot in my reissue 800 and it works but there is a hum that gets louder or softer with the master volume knob and it sounds like im only getting the low input tone regardless of which input im plugged into.i dont see anything off compared to georges pics but something aint right.but i do have sound and not blowing fuses or anything like that!

any ideas would be cool.even though im only getting the low input tone it sounds great!jason

jj jafar · Post by **jj jafar** » Sat Jan 29, 2005 6:57 pm

one other thing,the preamp knob isnt working either.i can turn it up and down but no change in the sound.damn im so close!

jason

jj jafar · Post by **jj jafar** » Sat Jan 29, 2005 8:26 pm

ok i figured it out,pins 2 and 7 on v1 were backwards.now the preamp knob works and both inputs are working right.although im still getting a pretty loud hum that changes with both volume knobs.im going to try some differant tubes and see if thats it.jason

Flames1950 · Post by **Flames1950** » Sat Jan 29, 2005 8:40 pm

I'd guess that in the input wiring confusion that there is simply a wiring mistake going to and from the board, the preamp volume got bypassed, and the switching on the input jacks as well. But again, I've got no info on the MV board layout George used (I did ask him for one of his CD's but I haven't gotten it yet) and without pics of how your amp is wired I'm at a loss to point out where to go. If I didn't have a baby to help take care of on weekends I'd just meet you somewhere since you're not THAT far away, but keeping "da Squeaks" entertained and working on amps don't mix well.
Did you have any way to post pics of that section of the amp? If you can get a digi camera and get a couple shots I can get them posted for you. I turned on my e-mail in my profile in case you can get some pics and send them!

jj jafar · Post by **jj jafar** » Sat Jan 29, 2005 8:56 pm

well everything seems to be workin fine now except the loud hum.the noise also changes while im playin,gets crackley and hissy.and when i turn both volume knobs twords 10 the noise agin starts craklin.any ideas on this would be great.the amp itself sounds pretty damn good aside from the noise.the master volums knob seems to get a little touchy once i hit about 6 or 7 as well,starts getting louder quicker,although not alot.thanks agin,jason

Flames1950 · Post by **Flames1950** » Sun Jan 30, 2005 6:08 am

As far as the Master seeming to get louder in a spot by 6-7, I usually find that all Marshalls have that "sweet spot" around there where you can actually hear the power amp start to roar. I like finding that spot and setting the volume just past it. (I rarely truly "dime" a Marshall.)
For the crackles and extra noise you can try swapping tubes, but on a new board install you may be better to start by going through your work solder joint by solder joint. Strange crackles and such are often a "cold" solder joint, where the wires and parts have enough solder to be in place solidly but aren't really making a good electrical connection. Go through it again, making sure the solder really flows through the joints and see if it doesn't improve the sound.
Glad the input problem was that simple!!

jj jafar · Post by **jj jafar** » Sun Jan 30, 2005 11:53 am

well i tried new preamp and power tubes and the hum is still there.the hum (especially at louder volumes)breaks up when i play harder or strum harder.im checking all my wiring but as of now dont see anything amiss.what i do know even with this problem is the tone kicks ass!very sweet and smooth.damn this hum!!!!

jason

Flames1950 · Post by **Flames1950** » Sun Jan 30, 2005 2:44 pm

I'd still check for cold joints first. If that doesn't pan out (and especially the hum it may not help) next I'd check for wiring problems -- the big one being to keep the green grid wires away from the blue plate voltage wires as much as possible in the preamp. Make sure the blue ones are laying at the chassis surface and many people lift the green wires up so they stay away better.
Even then you may find that some of the green grid wires need to be replaced with shielded cable. Before I convertedmy '78 to a non-MV it used shielded cable on the input grids from the factory.

jj jafar · Post by **jj jafar** » Sun Jan 30, 2005 3:19 pm

i used alot o new wire that george sent with the board.i was careful to route wires around the tube sockets to avoid noise,and did a fine job if i do say so myself.heres a new twist.on the reissue board it had a hum pot,of course now it doesnt.the reissue power tranny has a extra green wire that comes out by itself on the backside of the tranny.on the reissue it went to a dead lug,no other wires or traces and not grounded.so i put it on one of the empty lugs of the new board.maybe this has something to do with it.i had mentioned this wire to george and he didnt know what it was for.any ideas about this?i was thinking i might ground it but till i know what it is im not gonna.this mystery wire may be the problem.thanks for the help,jason

Post by **VelvetGeorge** » Sun Jan 30, 2005 5:21 pm

Yes! You need to ground that wire. It's the center tap for the heater winding. You can just solder to the nearest ground lug.
I forgot they started putting bias balance pots on the later RI's. That's why it went to the board.

George

jj jafar · Post by **jj jafar** » Sun Jan 30, 2005 10:42 pm

i kinda thought it might need grounded.i just used some alligator clips to ground it to see if it works,by god it did!hehe my first board is a success

this amp frickin rocks.this is the sound ive been after for a long time and all i had to do is build it

im hoping not having this grounded didnt damage anything.thanks george and everyone else for the help during this "quest for tone"jason

Post by **VelvetGeorge** » Mon Jan 31, 2005 12:42 am

Glad that fixed it. And that you like the tone. Enjoy.

George