Scott F: Please read. Another JTM question

Re: Scott F: Please read. Another JTM question

Sorry to bump this back to the top when it's been and gone. But I still have a few questions if anybody has the time to answer them. Well just one come to think of it.


The rectifier for the Heater voltage should not be confused with the HV (High Voltage) rectifier....just to clarify...
Click to expand...

Does this mean the 'black box' I would be removing is a rectifier? The heater rectifier, not the HV rectifier ArtieToo assumed I was refering to?

I'd love to send my amp to someone like Jeff and get all these problems ironed out but I live in the U.K. last time this happened I send the amp to Marshall Milton Keynes and it took them 6 weeks to do what I now know is a 20 minute soldering job. I live right in the sticks as well and I haven't found anybody who does this sort of stuff. So I'm trying to pick up as much information from here as I can. Once again, I thoroughly appreciate all the help I've received so far.

Many thanks,
Benja
 
Re: Scott F: Please read. Another JTM question

Scott_F said:
I just don't want to see you get killed yourself. There are LETHAL voltages inside that amp. Do you know what not to touch? Do you know how to drain capacitors? If not, that's where you need to start learning. Lots of great info on the net about this stuff.
Click to expand...

Amen, brother! Those filter caps need to be DRAINED because they hold a deadly charge for days and days after the amp has been unplugged. They hold more than enough current to send you to the next world and 400 volts -- almost 3 times your average wall outlet -- is WAAAAAYYY more than enough pressure to ram it through you!

Also, there is the One-Hand-In-The-Pocket rule for electricians -- NEVER have both hands in a live circuit or in a circuit where there are caps capable of holding heavy charges. If you get zapped on one hand, you get a nasty shock and probably a burn, but you live. If you have both hands in there, the current goes in one arm, through your heart and out the other arm. This is almost certain death. ONE HAND ONLY!...
 
Re: Scott F: Please read. Another JTM question

Rich_S said:
I had a business meeting right up the street from Jeff Seal's shop this morning, so I stopped by to meet him afterwards. (Nothing like standin' around shootin' the sh*t about guitars and amps on company time!)

Jeff's the real deal. He showed me a Marshall JCM800 head (one of those nasty channel-switching ones) that he has gutted and rebuilt as point-to-point with a Fender clean channel and a Marshall-and-then-some dirty channel. Nice workmanship throughout.

So, his advice on your amp is good. However, if you don't know the difference between the filament (heater) supply and the main B+ supply, either 1) take it so someone else, or 2) read and learn before you go messin' around in a tube amp. AX84.com and 18Watt.com are the places where I learned. And the first thing you need to learn is how to drain and check the filter caps before you start. At the very least, 400 VDC hurts.
Click to expand...


Dang, Rick's is open that early? :laugh2:
 
Re: Scott F: Please read. Another JTM question

Scott, actually it's "Sugar's" now....Haven't made an "inspection" of the new help.....soon!

Was a pleasure to meet and talk with Rich S, definitely a cool guy!

Benja, yes that is a full wave bridge rectifier you are removing....
let us know how it turns out!

Jeff Seal
 
Re: Scott F: Please read. Another JTM question

Hello to all.
I had a bash at the modification today. It was reletively successful, I'm still alive anyway! However, I didn't quite manage to achieve the desired results.

The amp works (sortof, I'll explain) but there is a substantial loss in volume. Although on a more positive note the amp sounds like it should again, just a lot quieter. If you remember me describing to you, Jeff, in another thread I think, that previously the volume drop was coupled with a very unpleasant distortion type sound. Almost like a ripped speaker. I did check them of course, they were/are fine.

Though most puzzling of all is that the master volume pot works backwards. 0 being maximum volume, though is still very, very quiet. I did remove a lot of the white 2-pin plug things to get better access to the PCB. I suspect I joined them back up wrongly. After posting this I'm heading to the Marshall website to try and find a schematic of the amp. This should help is finding exactly what I've done wrong.

I'm also concerned that my soldering let me down. I noticed that some of the solder had ran into adjacent tracks. I tried to pull it back with the soldering iron and got what I thought was all of it but I'm worried now that perhaps I didn't.

Jeff, when you described soldering the jumper leads in the position of the heater rectifier as top to top ands bottom to bottom, did you mean that the jumper leads should run parrellel to the top of the amp? This is how I soldered them in and thought I should check.

That's everything I can think of that might bear any relevence. If I've missed something out please ask.

Any ideas what's going on with my amp?
Thanks,
Benja

P.S. I live in lincolnshire, Exactly in the middle of a place called Grimsby, a place called Cleethorpes and another place called S****horpe. This is actually true. Yeah, it has great career prospects! Haha
 
Re: Scott F: Please read. Another JTM question

I can't believe they censored S****horpe! It's an actual town. It's real, look in a map! That's how rubbish it is where I live. They actually censor the names of local towns on the web so the rest of the world can pretend it doesn't exist!
 
Re: Scott F: Please read. Another JTM question

Benja, I'm almost 99% sure you crossed two of the jumpers...(don't you just love how they so easily get crossed)....If you can't find the info you need, I'll get it to you tomorrow when I get back to the shop..... no worries, but you would have thought they could have used something like differing connectors, given the number of them in there...hang tight...


Jeff Seal
 
Re: Scott F: Please read. Another JTM question

Hi Jeff,
I used insulated wire, a minimum amount of solder and I cut the spare off beyond the solder joint. Unless I connected the jumpers to the wrong terminals I can't see how they could touch at all. There's not enough slack on them. As I said before the jump leads run parrellel to the top of the amp. Is this the right way to connect them? I've left nothing in the hole where the capacitors were.

Many thanks,
Benja
 
Re: Scott F: Please read. Another JTM question

benjaturner said:
Hi Jeff,
I used insulated wire, a minimum amount of solder and I cut the spare off beyond the solder joint. Unless I connected the jumpers to the wrong terminals I can't see how they could touch at all. There's not enough slack on them. As I said before the jump leads run parrellel to the top of the amp. Is this the right way to connect them? I've left nothing in the hole where the capacitors were.

Many thanks,
Benja
Click to expand...

No, I don't mean you did the mod wrong, (you got that exactly right!) you plugged the white jumpers back in incorrectly.......Even I've done this many times!...patience, my friend....we'll get you going...... :)

Jeff Seal
 
Re: Scott F: Please read. Another JTM question

right. I see. sorry, I didn't realise these were called jumpers too. So this isn't a potentially damaging? I had my amp on for about 5 minutes trying to figure out as much as I could so I could describe the symptoms to you.

Also, a little off-topic (sorry), I noticed the power amps valves glowing much bluer than before. And the pre-amp valves seem to glow less bright. Do you know why this is?

And guess what happened the first time I plugged it in. The bloody fuse Blew! Haha, I guess I'm just not destined to be an Amp Tech, eh? I'm not sure which one, it's 0.5A. Not sure if this gives you a clue. It's very close to the on/off switch so I figured it might be the main power fuse but you can normally access these externally, right? I tried to trace it to find out where it lead, but got lost. I also figure that the main power fuse would have a lower resistance than 0.5A. I'm not sure which it is, but it does seem to blow a lot. I buy fuses at this rating in bulk now, it goes so much.

Thanks again Jeff,
Benja
 
Re: Scott F: Please read. Another JTM question

benjaturner said:
right. I see. sorry, I didn't realise these were called jumpers too. So this isn't a potentially damaging? I had my amp on for about 5 minutes trying to figure out as much as I could so I could describe the symptoms to you.

Also, a little off-topic (sorry), I noticed the power amps valves glowing much bluer than before. And the pre-amp valves seem to glow less bright. Do you know why this is?

And guess what happened the first time I plugged it in. The bloody fuse Blew! Haha, I guess I'm just not destined to be an Amp Tech, eh? I'm not sure which one, it's 0.5A. Not sure if this gives you a clue. It's very close to the on/off switch so I figured it might be the main power fuse but you can normally access these externally, right? I tried to trace it to find out where it lead, but got lost. I also figure that the main power fuse would have a lower resistance than 0.5A. I'm not sure which it is, but it does seem to blow a lot. I buy fuses at this rating in bulk now, it goes so much.

Thanks again Jeff,
Benja
Click to expand...

Benja, we seem to be posting on a continual "after" from each other... by the time I can give you an answer to one question, another one has been asked... which shows up as a response......(not intentional...)

In response to this question, Marshall was "kind enough" to at least keep the polarity straight on the factory jumpers...so nothing will be "damaged", but obviously "non" functional.....just recheck everything and you should be good!

sorry for the confusion......

Jeff Seal
 
Re: Scott F: Please read. Another JTM question

That's brilliant Jeff. Those schematics are really helpful, for the first time ever they seem to make sense. Not just funny little drawings with funny little lines anymore.

Again, I want to extend my utter thanks to you. I genuinely believe the Seymour Duncan Forum to be the best possible guitar related resource reference, ever. This is solely attributatable to you and some of the other members who regularly post here, answering questions which must seem inane to you by now, having answered them so many times already. I spend far more money on books and videos trying to learn as much as I can about guitars than I do on guitars, lol. Despite this I've never spend money on anything that has offered me half the infomation I've received here. Once again, my thanks.

I hope that if I keep learning when I grow up I'll be good enough to work in the guitar industry; my dream job is to be a guitar tech, touring with famous bands sorting all their gear needs! :-)

Though after the short while I've spent visiting this forum, I sincerely, and mostly, look forward to the time when I'm able to offer my experiance and knowledge to young guitar players like myself. Pass it on, as you have to me.

Benja

People like you make the Seymour Duncan Forum
 
Re: Scott F: Please read. Another JTM question

Hey Benja ive got a JTM60 what does this mod do to the sound of it?
Does it improve the tone at all??

Does Scott have any other mods for this amp to improve its tone?


thanks!
 
Re: Scott F: Please read. Another JTM question

Hey Benja ive got a JTM60 what does this mod do to the sound of it?
Does it improve the tone at all??
Click to expand...

Hi Tone?,
No, this mod does nothing to improve tone what-so-ever. Ideally it will not alter the sound of your amp. There is a possibility that your amp will be much nosier as a result of doing this to your amp though.

The basic idea is to improve reliability. One of the many design faults in the JTM amps is a heater rectifier positioned far too close to the valves which generate enough heat to create an enviroment far too extreme for delicate components. The heat from the valves continually 'unsolders' the component causing intermitant problems. Jeff Seal told me that the component is unneccessary to the porformance of the amp, and I'd lose very little, if any, tone compared to what I stood to achieve in terms of reliability.

That's all this mod does, improve the reliability of your amp. Hopefully, if I do it right, I'll have an amp that will still sound the same as ever, but it would break down as much.

How did I do Jeff? Did I sound like I knew what I was talking about? To Tone?, please wait for Jeff to confirm, what I've said to be true. I only just learnt this stuff in the last couple of days and am a real amateur. Please don't act on anything I've said, but seek the advice of the people who know what they're talking about.

Hope this helps,
Benja
 
Re: Scott F: Please read. Another JTM question

Just corrected the PCB board jumpers. Everything was fine for about 10 minutes then the problem came back, exactly like before. Any ideas?

Thanks,
Benja
 
Re: Scott F: Please read. Another JTM question

I'm sure eveything is wired correctly now. The problem is the same as before so I don't think it's likely to have been caused by any of the modifactions I've made in the last few days.
 
Re: Scott F: Please read. Another JTM question

Hi Tone?,
No, this mod does nothing to improve tone what-so-ever. Ideally it will not alter the sound of your amp. There is a possibility that your amp will be much nosier as a result of doing this to your amp though.

The basic idea is to improve reliability. One of the many design faults in the JTM amps is a heater rectifier positioned far too close to the valves which generate enough heat to create an enviroment far too extreme for delicate components. The heat from the valves continually 'unsolders' the component causing intermitant problems. Jeff Seal told me that the component is unneccessary to the porformance of the amp, and I'd lose very little, if any, tone compared to what I stood to achieve in terms of reliability.

That's all this mod does, improve the reliability of your amp. Hopefully, if I do it right, I'll have an amp that will still sound the same as ever, but it would break down as much.
Click to expand...

Can someone please put me straight on this. Did I get it right. I'd hate anybody to see this, do something to their amp and it turn out I got it wrong. Thanks.
 
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