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Guitar Amp Project

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psecody

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Well I'm about to get my income check back and was thinking about buying a new tube amp but I've also been wanting to get back into the electronics hobby and so I had an idea at about 2 this morning to design my own amp and learn more about them. While researching in google I came across the schematics to a Marshall 2555 Jubilee which is the amp I was going to buy two years ago but got screwed on my income tax return and ended up having to pay money instead of getting anything back. This is an amp from 1988 and when you find one they're usually about $2-3000 for the amp. I haven't had that kind of money in a long time, I was planning on spending $400 on a cheap tube amp but after looking at these schematics it isn't really that complex of an amp so I'm going to try building one (mainly because I would love a jubilee).

Anyway I don't have much experience with audio electronics (besides turning my amp on and adjusting the knobs) but I think I can do it. I need some help though so I figured I would ask the experts here. I'll also try to document the project as I do it so that anyone else interested in building this amp can look at it.

So these are the psu and the main board for the amp.

My first problem I've run into is I can't figure out where the psu attaches to the rest of the board I've got the psu figured out and already have most of the parts for it in my scrap bin and am going to get started on it this weekend then I plan on tackling the beast that is the main board. Question 2 just thought of would I want to use 1/4w, 1/2w or what for the resistors in the psu? I've never built any project that called for more than a 1/8w resistor so I figured I'd ask..
 

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MikeMl

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Where are you going to get the output transformer?
 

audioguru

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Will you dive down to a sunk Russian submarine so you can steal its vacuum tubes?
 

psecody

Member
hmmm well the vacuum tube comment I assume since there are still amps like this around that there is either some similar tubes that would work or that someone was still producing those tubes. There are companies that still produce tubes just for guitar amps. As for the transformer I looked up the manufacturer for the transformer and I figure I'll give them a call or something.... I'm not 100% about everything yet, I've been swamped with tests and school recently so I haven't had much time to research it but I just thought of those two questions and thought I would ask. I figured out the schematic question and also found out that there is a company producing kits for this particular amp so I'm guessing there is quite a good chance that parts are still being made.
 

crutschow

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Most Helpful Member
You're going to build a vacuum tube amp and you have an IC for your avatar??

That's a heck of a lot of parts to wire together. If you don't have a pcb for that it's going to be a really long project. I would suggest you contact that company producing the kits a get a pcb from them if you can, also some of the parts like the output transformer and the tubes.
 

psecody

Member
Found the output transformer and the power transformer. There is replacements being made for marshall amps and they have both the 100W transformers the output is $99 and the power is $109
100 Watt Output Transformer For Marshall Amplifier MOP-100 (17D020)
100 Watt Power Transformer For Marshall Amplifier MPT-100 (17D040)

You're going to build a vacuum tube amp and you have an IC for your avatar??
Yeah I'm more comfortable with IC's and such but having a tube amp is like a right of passage in the guitar world, the sound is so much warmer and you just can't get that from a solid state amp.

I don't think the wiring should be all that difficult, I would etch a pcb for it but if you look at high end amps they aren't done that way. "Hand wired" amps are what they do with high end amps (some crap about them being better) and it's just a board with wires run between the components.

I also found more clear circuit diagrams and even a wiring diagram and a placement board for the amp, though the 120, 220, 240 selector switch is omitted but thats not a big deal to me plus it can be added really easily though I will only use the 120.
 

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Mikebits

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Give the guy a break guys, geezo. My son is in 4th year college as a music major and he swears that the tube amps sound better. Me I could not say why. At any rate, for his setup he uses a solid stage amp all the way up until the final stage which is a pair of tubes used for the final amp (My son plays Cello, Violin, piano and his favorite is bass guitar). I would go this route if I were you, meaning solid state until final amp stage. BTW, each tube is like $200. as there is such a small market for these stone age devices, and be prepared to replace them from time to time.
 
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Hi,

before you start go visit Hoffman Amplifiers, Tube amplifier parts, tube amps, tubes this is about the best resource for tube amps out there. From parts (transformers, tubes, sockets etc etc.) to forums to to schematics to excellent advice and FAQ's. You may even want to change the amp you will be making.

I revamped my Vox AC30 T/B and inserted reverb. I think you may be well advised to include reverb into the amp now as it will be tougher if you should want to at a later stage.

Contrary to popular opinion tubes are more readily available than thought.

I encourage you to ignore the tube detractors, there is nothing in the rock world that sonically beats playing through a tube amp. Have played through many a SS amp, you cannot get the same from it as you can a tube amp, period. May SS amps have "tube" simulators built in. Forget the specs let your ears be the judge.

Don't be fooled by the wiring, this is the most critical part of tube amps, failing to follow convention will result in hum and crosstalk and other nasty things.

Oh forgot to mention, the voltages are very high and really Biiiite.

Please go visit hoffman amps before you start ........ you will save yourself time and frustration later.

Andrew
 

psecody

Member
yeah I was pricing the circuits to figure up a price and just the psu circuit is like $150 and minus the tubes I'm estimating about another $250 for the main circuit. I looked up the tubes and literally s%&^ a brick when I saw the prices, the amp has 7 tubes and the 3 smaller ones are $30 a piece for the cheap ones. The enclosure and the tubes are going to be the expensive parts I fear because I'm going to try and make it look as close to the real model as I can. Still if this ends up being sub $500 that is a steal for a tube amp, heck I was looking at a not-so-brand-name tube amp and it was like $800. I'm starting to figure out how it all goes together, it just blows my mind that someone figured out how to build one of these and get the sound they want out of them.... the whole electricity to sound part throws me for a loop I'm just not too sound savvy I guess.

he swears that the tube amps sound better. Me I could not say why
It's really hard to describe the sound difference to people that don't play but yeah there is a big difference in sound, for starters a 100W solid state amp is loud but not super loud where as a 100W tube amp will rattle windows and make it so loud you can't think, they're just a lot louder. Also the sound is more organic and warmer sounding, it has more feeling.... I'm not sure how to describe it. I'm not really wanting 100W for the volume but I figure if I'm going to build one why not go for the bigger one because it has selectable output between 50W and 100W which would be cool if I ever need it, though I usually just record direct into the computer so either way it won't matter. Anyway sorry for the extremely long story blah blah blah, I'm just really excited about this project, I've thought of doing it before in the past and it just didn't seem possible but now besides acquiring the parts it seems a little bit more achievable (more long banter) I've recently learned a new technique for tackling circuits... modules. I used to try and look at the whole picture and would get discouraged, now I try and break it down into more manageable pieces. Thanks for all the help guys I'm sure once I get some parts in and start tinkering I'll have more stupid questions to ask haha.
 

psecody

Member
holy crap thanks for that website Andrew, the prices there are so much lower than the electronics sites I was looking at (mouser and digikey) This is going to save me a lot of time and money I really appreciate it.
 

Mikebits

Well-Known Member
Cody, no need to give me your pitch as I think I was somewhat your advocate. You want to rock on through glass and gas, more power to ya, I have no doubt the sound is significant. I do however; just have one comment to something you said that I think deserves response.

It's really hard to describe the sound difference to people that don't play but yeah there is a big difference in sound, for starters a 100W solid state amp is loud but not super loud where as a 100W tube amp will rattle windows and make it so loud you can't think, they're just a lot louder.
A hundred watts is a hundred watts, whether it be tube or solid state, don't buy into any hype.
 

Mikebits

Well-Known Member
One more thing to think about. Specmanship, many manufacturers are somewhat dubious in their claims in regards to watts, and power, especially with amplifiers. The specs are often misleading and deceitful misleading honest people into poor purchases due to their trusting nature. Bottom line, an amp may claim to be 100 watts, yet barely deliver 60, I know this sounds crazy but I am sure many others here can explain how they get away with such practice. Best bet prior to purchase is to get spec sheets, post em here and get a honest answer. Hope I am right on this, someone may say I am FOS.

Where is Torben when ya need him? He is the music man, pretty good too. :)
 
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psecody

Member
Thanks I appreciate you defending my stance on the sound difference. As far as the power rating thing goes I'm not hard set on it having to produce 100W thats more of a mines bigger thing but the comment I made about tube amps being louder is one thing I've experienced over and over be it in a music store comparing SS vs/ tube or comparing my 100W SS to my cousins 100W tube, for some reason they get about twice as loud per watt as the SS ones do, I've noticed this even when the amps have the same speaker set up.
 

Mikebits

Well-Known Member
I know where you are coming from. I have eight electric guitars myself, some homemade, some antique. The question I pose to you is this, is a 100 watt rated amp really as it claims? There are tricks the industry uses to mislead consumers, I am hoping someone will explain these methods as I am not sure. P.S. Below is an image of my last guitar creation. Sorta Fender/BC Rich design...:)

 

Nigel Goodwin

Super Moderator
Most Helpful Member
There's nothing difficult about building a valve guitar amp, they are fairly crude devices, but it is VERY expensive, in particular valves and transformers are very pricey.

Mikebits: guitar amps and PA amps are honestly rated in RMS watts, and a valve amp will sound far louder than it's rating as well, due to the high distortion levels - distorted sound is far louder than clean sound. If you want the distorted valve sound a Marshall design is a great choice, probably the most sort after rock amplifiers.
 
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