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Question about capacitors and resistors


Adey

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Hi there, I looking at modding my Haze 40 as per this thread on the JVM forum; http://jvmforum.com/phpBB3/viewtopic.php?f=6&t=6049&sid=0c0471a3b3560bcaa456bf6d3f8e2f47

 

Looking online for components, I'm a bit confused about exactly what kind of resistors and caps to get. I'm good with a soldering iron, but so far my experience is limited to wiring guitars, and building pedals from kits. There are options like voltage, wattage, tolerance, min/max temperature and various other options I've never heard of.

I presume the mods I'm looking at are tone circuit mods so wont need high voltage or anything, but I'm not sure i'll be able to order the right parts.

 

Is anyone here able to deduce from looking at that thread, what components I should get? I know what values to get (i.e 1nf cap and 2.7k resistor etc) but it's the other options that are stumping me.

 

I tried asking on the JVM thread, but I assume my post was declined because I havnt introduced myself on that board, and I haven't done that, because I don't actually own a JVM. What ever I do there is gonna be considered a bit cheeky, so I'm asking here instead.

 

I promise I won't electrocute myself btw, I understand the dangers involved, and will take the nessasary precautions.

 

thank you!

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That's fair enough, I can appreciate that. Maybe if I look at the components I wish to replace I'll be able to see what type they are and get the same type, but of different values.

 

Thank you for replying though, cheers

 

:thu:

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Hi there' date=' I looking at modding my Haze 40 as per this thread on the JVM forum; http://jvmforum.com/phpBB3/viewtopic...56bf6d3f8e2f47

 

Looking online for components, I'm a bit confused about exactly what kind of resistors and caps to get. I'm good with a soldering iron, but so far my experience is limited to wiring guitars, and building pedals from kits. There are options like voltage, wattage, tolerance, min/max temperature and various other options I've never heard of.

 

First of all, a caveat - working on amps - especially tube amps - is a whole 'nuther world vs. working with pedals and guitars. SAFETY needs to be your number one concern because amps can KILL YOU. So if you're not sure of how to open one up and work on it safely, that should be the very first thing you learn about.

 

Even an unplugged tube amp can store significant charge in the filter caps - enough to give you a very nasty electrical shock - so you'll need to make sure the amp's unplugged for a day or so before working on it, and also you'll need to learn how to safely drain the filter caps. Yes, even if you're only planning on working on the amp's tone stack.

 

Most amps use 1/2 watt resistors. Carbon comp or metal film? I like the later, but some people argue that the former has "more mojo" - whatever that means. ;) Tolerance? Stick with 1% tolerance if you can. "The best" type of capacitors to use is a can of worms that I don't really want to open here - suffice it to say that different types are preferred for different things by different people... you're probably safe in sticking with whatever the stock types of caps are and playing with slightly different values until you find the sound and response you prefer.

 

I presume the mods I'm looking at are tone circuit mods so wont need high voltage or anything, but I'm not sure i'll be able to order the right parts.

 

Is anyone here able to deduce from looking at that thread, what components I should get? I know what values to get (i.e 1nf cap and 2.7k resistor etc) but it's the other options that are stumping me.

 

I tried asking on the JVM thread, but I assume my post was declined because I havnt introduced myself on that board, and I haven't done that, because I don't actually own a JVM. What ever I do there is gonna be considered a bit cheeky, so I'm asking here instead.

 

I promise I won't electrocute myself btw, I understand the dangers involved, and will take the nessasary precautions.

 

thank you!

 

Forgive me for putting such an emphasis on that, but it really is important! :)

 

Have you had any experience with desoldering things on a PCB? While I've never worked on a Haze, I suspect they're not made with point to point construction, so you're going to need to desolder things off of circuit boards, which can be tricky - especially if the boards use thin traces that can be easily lifted or damaged if you do it wrong. I'd suggest getting some scrap electronics (an old broken radio or whatever) to practice on first before you risk damaging your amp.

 

Finally, I would recommend asking questions over there if you can. Introduce yourself and be honest about why you're there, and I suspect they'll be cool about it. The people who have actually done the mods in question will know more about what to watch out for than people like me who have never opened up one of those amps...

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I heartily suggest if you have not already, you should get the schematic for the amp: https://www.thetubestore.com/lib/thetubestore/schematics/Marshall/Marshall-Haze-MHZ40C-Schematic.pdf

This will at least define the existing values and voltages. I'm with Phil on getting the tightest tolerances you can, particularly on 1/4W resistors, but be prepared to need to go up or down in value because of the tolerances.

I would also suggest that you examine the components you are planning to replace and match them as closely as possible, except, of course, for value.

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First of all, a caveat - working on amps - especially tube amps - is a whole 'nuther world vs. working with pedals and guitars. SAFETY needs to be your number one concern because amps can KILL YOU. So if you're not sure of how to open one up and work on it safely, that should be the very first thing you learn about.

 

Even an unplugged tube amp can store significant charge in the filter caps - enough to give you a very nasty electrical shock - so you'll need to make sure the amp's unplugged for a day or so before working on it, and also you'll need to learn how to safely drain the filter caps. Yes, even if you're only planning on working on the amp's tone stack.

 

Most amps use 1/2 watt resistors. Carbon comp or metal film? I like the later, but some people argue that the former has "more mojo" - whatever that means. ;) Tolerance? Stick with 1% tolerance if you can. "The best" type of capacitors to use is a can of worms that I don't really want to open here - suffice it to say that different types are preferred for different things by different people... you're probably safe in sticking with whatever the stock types of caps are and playing with slightly different values until you find the sound and response you prefer.

 

 

 

Forgive me for putting such an emphasis on that, but it really is important! :)

 

Have you had any experience with desoldering things on a PCB? While I've never worked on a Haze, I suspect they're not made with point to point construction, so you're going to need to desolder things off of circuit boards, which can be tricky - especially if the boards use thin traces that can be easily lifted or damaged if you do it wrong. I'd suggest getting some scrap electronics (an old broken radio or whatever) to practice on first before you risk damaging your amp.

 

Finally, I would recommend asking questions over there if you can. Introduce yourself and be honest about why you're there, and I suspect they'll be cool about it. The people who have actually done the mods in question will know more about what to watch out for than people like me who have never opened up one of those amps...

 

I am aware of the dangers involved yes, but I still appreciate your words of warning. I've always taken safety very seriously, in fact I've been wanting to try these mods for 2 years or so, but I put it off because I realised I didn't have the experience to do it safely (for my amp health or my own).

 

I have removed components from circuit boards also.

I try to keep the iron in contact for no more than 3 seconds when soldering/desoldering. If the solder won't flow by that time I know something is not right. But I'm at the point now where I am consistent with a soldering iron. I even once salvaged all the components off an old DVD player as a way to practice and have some bits in stock.

 

Thank you very much for your advice, I respect your knowledge and experience and I really appreciate you giving your time to help me. :thu:

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[uSER=287761]Daddy[/uSER] mack and Danocoustic

 

Thank you also. I will look at the schematic and check the existing components and make sure I get the same type but with different values. I'll also get the tightest tolerance I can. I'll also look at getting a cap discharging probe, just to be on the safe side.

 

Thank you all chaps!

 

;)

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Yes, you should always double check to make sure the amp is unplugged, and discharge the caps first before proceeding with anything else.

 

You can make a capacitor discharge probe yourself, or you can buy them pre-made. Here's one:

 

https://www.stewmac.com/Luthier_Tools/Tools_by_Job/Tools_for_Electronics_and_Pickups/SnufferStick_High_Voltage_Discharge_Stick.html

 

Good luck to you with your mods, and please keep us posted as to how it goes with them, and don't hesitate to ask if you have any more questions. :wave:

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having been on the receiving end of a capacitor discharge many years ago [thankfully not from an amp, but from a mainframe computer], let me just say it is a sensation to be missed, and not to be repeated if at all possible. Dano is correct about the discharge rate, too...I've seen amps dump a $#!+load of voltage after a month of sitting unused...my VJ is an example... Just to be 'safe', after two months waiting its turn on the 'mod bench', I routinely discharged the caps [through an ancient analog volt meter, ca 1970]...still saw major voltage discharge [pinned the needle hard on 250V setting]...now of course, as we say, it ain't the volts that kill ya, it is the amps....but dang!

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Well I have some developments today.

Back when I had the stock speaker in my amp, I tried taking the back of the amp off, to see what difference it made, and it didn't seem to help at all.

I bought a G12k-85 a week ago (dated 1985 no less) for a bargain £25. I tried it today with the back off again, not expecting much, and lo and behold, it took away the excess bass and even added more chime and clarity too. I can now have the bass knob turned up a bit which is adding some nice colour and overtones to the higher frequencies too, making the amp sound better overall.

 

I have rehearsal this Monday, so I can test it out properly, but it's looking good!

 

I also had a look at the circuit board, and to do these mods, I would need to separate the board from the chassis, and so have decided to leave the mods for now, and see how it's goes. I have also found a local-ish amp tech who looks very good and could probably do the mods for £30 if I feel like it's needed. These mods would turn my amp into a JCM 800 2203 BTW, as the topology is very similar.

 

So I kinda feel like I've wasted your time a bit, but at the same time, I have learned a bit and gained some wisdom, so maybe not. Either way I really appreciate your time in helping me, you're the hero I needed but didnt deserve haha.

 

Thank you all guys, you're all top blokes (as we say 'ere in Plymuff)

 

Cheers :cool11:

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