Slighty OT- Marshall head problems

[ninoman123]

I bought a used Marshall valvestate 100 watt head for 50 bucks.  Doesnt work (of course) which is the reason I bought it. Changed the preamp tube and fuse. The amp turns on but I'm getting no sound. And suggestions? Should I email Marshall? Or am I wasting my time and this is unfixable. Thanks for any help in advanced. Also any leads to websites/other forums would help too. I dont know where to start.

[jjucius]

Sorry to say but check your output transistors. i had a valvestate once and the trannys went out and had the same problems you have. if you dont want to fix it i have some things to trade you for it. i'm looking for a case and pots for an amp i'm building. i cant remember what it cost for the trannys but i know it was up there to have it done at the repair shop.
Good luck
Joe

[ninoman123]

Well the headphone jack output works if I only put the jack in halfway. It sounds distorted though, so am I am getting some output, but I cant get the loudpspeaker outputs to work quite right yet.  :?

[jjucius]

Well thats the same thing that i went through. i got some sound through the speakers distorted if i had the volume cranked. and that was only on the clean channel the distort channel i had no output at all.
hope this helps
joe
also make shure your running 8ohms at your speaker

[ninoman123]

Both clean and dirty work. Dont hafta turn the volume all the way up to hear it. The reason why it was distorted was because I had it turned all the way up. So clean and dirty work fine, but like I said only on headphone jack and only when the jack is halfway plugged in.

[ninoman123]

I might add that I dont have a cabinet yet so Im using stereo speakers. They run at 8 ohms. I kinda have them wired funky so heres how it goes

Input to amp-----input to 1/4 inch phone jack----tip to + of speakers and ring to - of speakers

That should be right but I dont really know maybe that helps some. Is it possible for just some of the output transistors to fail? Would that be the cause of me only getting headphone jack? I have a schematic for this amp if anyone needs it.  

Which are the output transistors? The ones with the big heat sinks on them? Those are BDV65s and BDV64s. Which transistors could I buy to replace those? Ill check NTE.

[jjucius]

The only other thing i can think of is your output transformer. i would take it in to check that. wish i could help more but i'm running all tube amps now.
Joe
yes those are the ones, you have to replace them in sets and yes its posibal for only some to fail but replace them all and make shure they dont touch the heat sink and when you solder them to use a heat sink so they dont get to hot i frided a set because i over heated them. your spakers should be ok.

[jjucius]

Check here for help
http://www.blamepro.com/CGI-BIN/cutecast.pl?session=AiamauHRO4sJ5yUCs35eMDFl3V#2

they helped me
Joe

[ninoman123]

Alright cool. I guess I'll order some of those from NTE.

[petemoore]

Similar deal,..sorta...little amp forum thread OT here...
 dudes Rockford Fosgate boom box thumper amp I think has output problems, due to being run at 1/2 the minimum speaker output ohmage  :roll:
 I'm figureing on measuring the output transistors voltages, [hopefully they're not all blown and can 'build' some voltage references]...then try to get the ones with 'wierd' voltages replaced or somehow otherwise cajoled into 'operational status'.

[ninoman123]

Yeah, I'm gonna test voltages of those today too. Just wanna check to make sure they are blown.  Seems this is the problem though.

This isnt entirely OT. lol. I mean...GGG has schematics for practice amps....soo.....I guess amps are kinda on topic. I dunno. lol.

[petemoore]

Yeah, I'm gonna test voltages of those today too. Just wanna check to make sure they are blown.  Seems this is the problem though.

This isnt entirely OT. lol. I mean...GGG has schematics for practice amps....soo.....I guess amps are kinda on topic. I dunno. lol.

OT?...[I may be alone, I kind of like to see an amp thread, going past one is no big deal to me, picking up little amp tidbits here and there never hurt a stompboxer...High Voltage shocks aside]. I like to put a warning of potentially lethal voltages in here.
 To me amps are like soles for shoes for the stompbox walks of life ..can't hardly take the first steps without them...just don't cut your nose off building them up/shaping them.
 Anyway, I pulled open to find no workable voltages on IC's
 Super mini IC's, mini IC's, and rows of what looked like supply and output transistors, alot of large caps...and...baked resistors right next to the ultra mini IC looking things, I didn't take the time to magnify and count the connections...it'd be like repairing fried roachlegs...done kaput..slick/high tech design, too hard for repairs, get another board I sezz...maybe re-use the larger, more expensive components...then just buy a new one and be super strongly emphasize connecting it 'right'.
 200w a side, 20-20khz, .1% distortion...pretty respectable specs...alotta poop in there...too bad it don't work no more.

[ninoman123]

Ouch. Yah I only found one resistor that looked fried. Might not have been. and Some of my wires to the power supply were fried. Nothing else looks fried, but Im at work ill check voltages when I get home.

Yah i dont really see why its OT either. Amps and stompboxes go hand in hand.

[ninoman123]

Hmm... I tested voltages and wasnt getting much, looking at some of the solder pads I wondered something.  So i tested with my DMM and some of the legs of the output transistors didnt even connect with the trace they were supposed to. How could this happen? This thing doesnt look modded by anyone. Funky...Ill try to connect the traces and see what happens.

[ninoman123]

Scratch that, the traces are inside the board. Back to testing voltages.