New Host, Founding Father of Marshall!!!!

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Re: New Host, Founding Father of Marshall!!!!

Postby bmi on Sat Sep 12, 2009 4:20 pm

Thanks a lot ken, you give me the key and save my day.
All apologize, i've read all the thread and remember that you were on the beginning of the story but have not understood it was 63.
You was right the noise is always here when i turn back the 2 volumes. It changes when i turn the tonestack being more clear with treble or muddy with middle. The noise is there when nothing is plugged. I have made all basic tests i can and just get with your expertise the confirmation that it does come from the big caps.
Sorry but i need again your help to identify the caps in the amp...it could be selection 1 or selection 2 in this pictures or both, what do you think it is?
Image

Now i'm looking for a basic method to test the big caps because i have to found the same caps then test it again to check if they are good before switching the bad ones. I have just a multimeter with me :oops: (and some caps)
Is it possible to make a miracle with just a multimeter?
bmi
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Sat Sep 12, 2009 4:43 pm

Well it is not very easy to check a High Voltage Capacitor with a Multi Meter,it would be quicker to lift one leg of each capacitor one at time and roughly connect a new one until you find the one that is causing the problem,BUT make sure that each time you dis connect one of the capacitors that you dis charge it with what ever you have as if you do not you will get a nasty shock as i do not think that you will find it with the first capacitor. There will be a spark when you short each capacitor out but when but when you get to the correct one there will be either no spark or very little spark so you will know that you have found the right one. Make sure that you change the capacitors for the same value and the same working voltage.

I hope that all goes well and by all means shout for help if you need me.

Regards

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby bmi on Sat Sep 12, 2009 4:59 pm

Thanks ken for your help...i will keep you abreast. :thumbsup:
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Re: New Host, Founding Father of Marshall!!!!

Postby demonufo on Sat Sep 12, 2009 7:58 pm

The only way to test electrolytic caps with a multimeter (and it isn't very reliable) is to have another brand new cap of exact same spec to compare to.
Select the highest Ohms rating on the meter. Count in seconds how long it takes for the multimeter to go out of range (the resistance should be building up), and then do the same on the new capacitor.
If the old one builds up considereably slower than the new capacitor then it may well be that the ESR has gone wayward and the cap is bad.
But then some manufacturers had higher ESR than others.
The only decent way to test electrolytic caps is to have a decent meter that will measure both ESR and leakage currents, and they're not cheap.
Sorry for butting in Ken, just trying to save you some time here.
Last edited by demonufo on Sat Sep 12, 2009 8:49 pm, edited 1 time in total.
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Sat Sep 12, 2009 8:18 pm

Not saving me any time at all and no need to say sorry but the only thing that i will say is that the way that you explain is all very well but it will not tell you how far off from the original value you are.

We are talking about 33uF and they could be down to 12 uF so you will see a difference with a multi meter but to the average guy with minimal technical knowledge confusing.

As the guy was trying to sort this out him self and had minimal technical knowledge i felt that this would be better for him.

You are right of course your method to someone with a background in electronics is the correct one and this sort of person would no doubt have a capacitance meter any way.

Thanks for the reply.

Regards

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby demonufo on Sat Sep 12, 2009 8:49 pm

:lol: Guess I should have said something about the actual value! (My bad!)
It's just that more often than not I find bad caps that are still within spec on the value, but leak current like a sieve.
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Re: New Host, Founding Father of Marshall!!!!

Postby Strat59 on Sat Sep 12, 2009 11:52 pm

Wise words Ken :thumbsup: High Voltage + Inexperience = :no_no:

Being a New amp & under warranty is better to take to an Auth Service Guy to
rectify (not the valve kind) :) IMHO
"Blues players don't mess around with a guitar, they hit the bloody thing"........ Rory Gallagher
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Re: New Host, Founding Father of Marshall!!!!

Postby bmi on Sun Sep 13, 2009 3:33 am

Thanks for your help strat59 but i'm not really completly uncompetent. I have got 15 years ago a master degrees in electronic & automatic but never work in the field of my life(work as studies engineer on billing systems for telecom operators, ie software part). Feel too bored by my studies where i never see a real schematic, they were all theoric. So i know what is high voltage. Amps makes me coming back into the field of electronic but i have to see all again. I already do services and light mods in my amps and have the project one day to build my own original amp when i will get all the knowledge(perhaps end of next year). Of course i will take it on a technician if Marshall take care of it, if not i will do it myself it will be more simple. I appreciate all help and be very happy that ken put the finger on something i think for now a while, that is hum going from bad big caps. I already have this issue on a supersonic (and i think a lot of supersonic have this issue) but never change the caps because removing the pcb was a nightmare.(yes i can unsolder them from the top but it's not a clean job)
So thanks for all your help to all and especially to ken for is high valuable expertise (he puts directly the finger on it). :cheers:
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Re: New Host, Founding Father of Marshall!!!!

Postby bmi on Sun Sep 13, 2009 4:42 am

By the way i'm wondering what kind of wires you use in 60th?
We find today cotton insulated wire but some have only one bare wire inside and other 4 or 5.
By experience and probably due to the skin effect, using in a guitare a simple bare wire or multiple bare wire changes the sound.
So what do you use in 60th?
bmi
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Sun Sep 13, 2009 6:14 am

I understand that this is a new amp so as has been said take it back under warranty first and i cannot see that you will have any problem getting it sorted.

As for the wire question single stranded wire was the order of the day.

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Re: New Host, Founding Father of Marshall!!!!

Postby Strat59 on Sun Sep 13, 2009 12:02 pm

Hi bmi , sorry didn't mean to infer you didn't have prior experience. Was just
following up the comment from Ken , that anyone without experience
is better advised to go to a good Tech for safety sake.

Also I mentioned that to just let you know with a new amp if you do anything
to it yourself , it will void your warranty in case you have to send it back. :thumbsup:
"Blues players don't mess around with a guitar, they hit the bloody thing"........ Rory Gallagher
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Re: New Host, Founding Father of Marshall!!!!

Postby bmi on Mon Sep 14, 2009 4:02 am

No problem, i appreciate your advices. Perhaps i have to tell you another story so you will understand better my position. I have bought 2 years ago a supersonic in a UK shop too, this one a really brand new. There was a static noise too. I have tried to register the amp here in France but Fender France tell me that they are not the same company than Fender UK and if i have bought the amp in UK i have to register there. I have tried using the website but it was not available to another country than UK. Come back to the seller and it tells me to bring the amp to my technician and to send him the invoice. I have bring the amp to my technician and he has changes many resistor with metal/film but it changes nothing. I was not happy but... I understood later that it probably comes from the big cap and he was to lazy to umount the pcb and change them. So this week i will see what happend with the seller and if Marshall take care of the amp or not, if it's like Fender....
By the way i have asked the tracking number of the amp to the seller and this one never give it to me. I have told him that i want to check the amp in the depot office of the carrier before the truck was before my home to check in particular if there was nothing wrong with the OT. Sometimes the OT are so bigs and they move when there is a shock. I think i understand now why he didn't give me a tracking number. :?
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Re: New Host, Founding Father of Marshall!!!!

Postby zaphod_phil on Mon Sep 14, 2009 1:15 pm

bmi wrote:By experience and probably due to the skin effect, using in a guitare a simple bare wire or multiple bare wire changes the sound.
So what do you use in 60th?
G3SDW wrote:As for the wire question single stranded wire was the order of the day.

bmi, the skin effect only becomes significant at the very high end of the audio spectrum. At 60Hz the skin depth is 8.5 mm, while at 10kHz it's still 0.66mm. Typically we attenuate frequencies above 10kHz in most guitar amps, as they tend to make distortion sound harsh, and also most guitar speakers don't reproduce frequencies that high. There is also no benefit in using multi-stranded wire against skin effect unless each individual strand is separately insulated, like for example Litz wire, which Ken as an amateur radio operator will be very familiar with. :) So personally I very much doubt that the normal human ear can hear any difference between solid wire and multi-stranded wire of the same total diameter used in a guitar amp.
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Re: New Host, Founding Father of Marshall!!!!

Postby bmi on Mon Sep 14, 2009 2:04 pm

Using the skin effect was a wrong choice for me to express what i wanted to say.
Just want to say that when you have 4 conductors it acts as 4 signals IMO.
It's easy to check in a guitar. Use multiple wires cable inside then in the cable that goes from the switch to the jack, cut and decrease the number of wires. You will notice that first the signal become less strong and in the same time it becomes less brigth as if many wires add brightness. You just have many signals that's were come the brightness.
I use for my cabs a 1 bar wire cable and the saturations are more accurate and a bar 0,4 mm cooper gold plated in my gibson.(and i know the best conductor is silver)
That's why i ask what they used in old amps, for me the number of wires in a cable has an importance. (and there is many more than then number of wire)
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Re: New Host, Founding Father of Marshall!!!!

Postby bolero on Tue Sep 15, 2009 5:23 am

wow, I just read through this thread, amazing....and thx so much Ken, for taking the time to post here, very interesting stuff!!

do you have any good stories about the bands/musicians that must have frequented the shop early on?

ie: did the fellows in the shop think Pete Townshend ( or was it Entwhistle? ) was off his rocker when he wanted 8x12 cabs?

were you around when Hendrix/Cream etc started using the amps? heck, did you even like that sort of music back then?

also I find it interesting that the Beatles never used any Marshall gear

cheers
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