AFD100 help request

[fecska]

Hey,
i'm new to here, and also new to amp building.
I know here it comes the "you should start with a smaller", and so, but i really want make THIS, not an 5W transistor amp.
I have the needed resources, except the knowlegde 
I learn IT-enginiering, and live in a special college, where electric engineers, and IT engineers works together in big project. So i have the required tools, and parts.
For me the AFD100 is special because the power scaling on it, so i can get great tones on low volume.
The only schematic i found, is so unclear for me. I can't get some of the markings also, and the structure of the schematic also disturb me.
So I ask for your help an tips to start this project.
I'm in the planning part, and will start to work, when i feel i'm ready.
The first problem is to read the schematic. It constains markings what i never seen before. I also miss the transformers from the schematics.
F.e. What is the little rect. with a circle in it? (VR1B)

Thanks for your help, and i hope i can play on my amp next year :)


Some things i found:


http://www.tonymckenzie.com/afd100_review.htm
A HUUUGE review. It constains some important info f.e.: it uses the same transformers as the JCM800.

[PRR]

> "you should start with a smaller"

You should start with something smaller.

> make THIS, not an 5W transistor amp.

A 5-W Champ tube-amp is fairly challenging as a first project.

> AFD100 is special because the power scaling

You can variable-power a Champ. I did some experiments with a "super Champ" simply varying the screen voltage with a 2-Watt potentiometer.... worked fine on the bench (did not get any further). I think I have a sketch of an even simpler "Third-Watt" amp with variable power floating around.

HIGH!-power variation is more complex, dangerous to work on, and often frustrating to beginners. The least error can blow-up many dollars of parts.

This power control is exceptionally complicated. Why are there four bias-amps all doing the same thing?

I really think this was designed for LOW-LOW-cost manufacturing. That they could throw-in dozens of extra parts for no good reason and not care because it didn't affect final price.

> the structure of the schematic also disturb me.

Disturbs me also. It was drawn on a computer, which kept track of connections, so stuff is dropped here and there without much consideration for human understanding.

> markings what i never seen before

Which markings?

This is really just the main PCB. 97% of the amp is on the PCB. Things like transformers connect to marks like "CN14". There are a LOT of "CNxx" marks. The transformer drawings probably show that the two ends of a 360VAC winding shall be in a connector at positions 19 and 21 (CN19 CN21). But I see at least *five* transformer windings (there may be more). That is a LOT of small windings, so probably not the exact same power transformer as other Marshalls. Also it looks like these are connector numbers not wire numbers. CN40A looks like it must go top-left, to CN23A. So there must be a wire-harness plan showing the number at both ends of each wire.

> F.e. What is the little rect. with a circle in it? (VR1B)

This is disturbing. "VR" is usually "variable resistor". And VR1B is a variable resistor (Volume potentiometer). VR3 VR4 VR5 likewise. However all three legs of these pots are shown. "VR1B" seems to be a *fourth* leg on a 3-leg device. I would *assume* it is the pot shell. VR1B seems to go to AGND through a medium capacitor, which would drain radio waves without allowing large DC or 50/60Hz AC to pass to the user and cause a shock.

[eleventeen]

I'm going to go out a limb and tell you with perfect certainty that project is 100% unsuitable for a first build. You are envisioning two ends of the amp building universe, that of a 5-watt solid state amp, and this 200-watt beast. In between are much more manageable projects where you can learn perhaps 50 skills that are very hard to transmit to another person: You just have to carve up metal or wood and solder stuff in place and screw it up some number of times before you either acquire the skills or come to the conclusion that it's more work than it's worth. Because you could buy that amp (if it was so important) and resell it for $2-300 less in a year or two but you will not be able to buy merely the power and output transformers and tubes for that much. Never mind the pots, connectors, knobs, resistors and capacitors, screws, mounting hardware, jacks, tube sockets, amp corners, handle, cabinet, rubber feet, pilot lamp and 2 dozen other things. What do you do if you get $600 into it and hate how it sounds, or it has some weird hum you can't get rid of?


I assume you'll pay zero attention to what I am saying, so good luck.

[fecska]

VR1B seems to go to AGND through a medium capacitor, which would drain radio waves without allowing large DC or 50/60Hz AC to pass to the user and cause a shock.

You're must be right, because switches also have this little stuff, so it should be for the controls of the amp.

Which markings?

For example:
HS1 and HS2 little long rectangles.
That halfmoon between CN11 and CN13
The little rings named MT1, MT2 etc.

Why are there four bias-amps all doing the same thing?

It has the feature of auto biasing the 4 PowerTube while changing the power.

HIGH!-power variation is more complex, dangerous to work on, and often frustrating to beginners.

Im not totally beginner in electronic, but in amps. I also worked on high voltage inverters, and generators, so i can respect the voltages :)
And I want a LOUD amp, as i have little 2-15W amps, and dont want to pay 2000$s for a tube amp, what I can make in optimal case from 5-600$, meanwhile have fun :)

 Thanks for answering me! I get fired from most forums, because "GTFO and build a 1W amp from transistors" :)

[fecska]

I'm going to go out a limb and tell you with perfect certainty that project is 100% unsuitable for a first build. You are envisioning two ends of the amp building universe, that of a 5-watt solid state amp, and this 200-watt beast. In between are much more manageable projects where you can learn perhaps 50 skills that are very hard to transmit to another person: You just have to carve up metal or wood and solder stuff in place and screw it up some number of times before you either acquire the skills or come to the conclusion that it's more work than it's worth. Because you could buy that amp (if it was so important) and resell it for $2-300 less in a year or two but you will not be able to buy merely the power and output transformers and tubes for that much. Never mind the pots, connectors, knobs, resistors and capacitors, screws, mounting hardware, jacks, tube sockets, amp corners, handle, cabinet, rubber feet, pilot lamp and 2 dozen other things. What do you do if you get $600 into it and hate how it sounds, or it has some weird hum you can't get rid of?


I assume you'll pay zero attention to what I am saying, so good luck.

I pay attention what you saying, thats why i wrote here :)
In my university for example, we should make a PC game for homework, after a semester of programming, so I know what the feeling of "screwing it".

As I mentioned, I'm not totally beginner, i can solder stuff, carve metal and wood,  and in my college i have the most of stuff because its has an electoinc workshop. And there are some people who knows it well, but i cant found anyone, who built an amp, especially tube amp.

Answering your question: I work on it, until i get what i want, and the best part of amp building, you not have to pay the whole amount, so you can build it gradually.

So my other question is: this is not the full schematics, and i think no one has the full wiring manual, so is it possible to figure it out together or its totally impossible? :)

[fecska]

Why are there four bias-amps all doing the same thing?

read on an article, you can put different tubes f.e.:2x6550 and 2xEL84 etc.


One More Thing:
I'm also interested in building a JCM800(lot of manuals and resources) with an implemented power scaling. Is this possible?

[eleventeen]

I'm glad you took my message without being insulted. I don't want to discourage you from building amps if you want to, just that this is a highly ambitious build. Coming from out of the blue and not knowing you, I/we have no idea how much skill and what level of tools/machines you have available to you. Did I mention time?


One thing I *can* tell you is that if you can find a bad 200 watt Marshall head that you can buy used as a repair item for cheap, that would include the transformers, the cabinet, the chassis, perhaps some tubes and a load of other parts, you could be miles and miles ahead of the game, and buy such a thing very likely for less than what the parts from same would cost.

[PRR]

> auto biasing the 4 PowerTube

There must be ANOTHER board with four bias trimmers. Also some re-scaling between Plate voltage and Grid voltage, because they do not change exactly proportional.

I see other signs that there is "more". Each power tube cathode has a current-sense resistor with another 47K and a clamp-diode. The power supply after CN14 CN9 goes to "+5D" and "DGND", which suggests Digital stuff, but no significant digital on this drawing.

It isn't THIS complicated to get a good-playing BIG amp with variable power.

This is a giant puzzle with many missing pieces. A deep study of older (better drawn) Marshalls will help a lot. Good Luck.

[fecska]

Did I mention time?

Nope, I counting ~1 year for this project.

One thing I *can* tell you is that if you can find a bad 200 watt Marshall head

In my country there is not a big culture of tube amps. Most likely you cant find a working amp for sale in this price range, nor dont working amps.

> auto biasing the 4 PowerTube

There must be ANOTHER board with four bias trimmers. Also some re-scaling between Plate voltage and Grid voltage, because they do not change exactly proportional.

I see other signs that there is "more". Each power tube cathode has a current-sense resistor with another 47K and a clamp-diode. The power supply after CN14 CN9 goes to "+5D" and "DGND", which suggests Digital stuff, but no significant digital on this drawing.

It isn't THIS complicated to get a good-playing BIG amp with variable power.

This is a giant puzzle with many missing pieces. A deep study of older (better drawn) Marshalls will help a lot. Good Luck.

OK AFD100 rejected

What about a JCM800 with power scaling?

I think YJM100 also has this as a "level" setting. Could i implement that in a "retail" JCM800?

[Ritchie200]

I would implore you to build the JCM800 first before tackling something like an AFD100.  Like was mentioned earlier, there are all sorts of little things you will learn along the way that would help you with your dream build.  The JCM800 is a well traveled design, relatively simple layout, and will get you past the face palming you will inevitably be going through along the way (something we all have done and continue to do... ).  These will be priceless (and I do mean $$$$) bits of knowledge that will help you when you build your AFD.  Plus, if your country is craving for good tube amps, you could sell the JCM800 upon completion to help fund your dream build.  You may also find that with some tweaking and incorporation of some of your favorite AFD features, your custom boutique FECSKA800 will surpass anything the AFD can do and sound better to your ears.  Like PRR said, many times the sonic solution in manufacturing is the cheapest route, not necessarily the best sounding route.


So, MY advice is to forget the 5w solid state amp and build something that will annoy your neighbors!  Doug has everything you need here to build an 800.  Jump in, plan to make some mistakes, let the forum help you when needed, and have fun!  Oh, and by the way, if you are used to high voltage stuff - you know to keep one hand in your pocket when hot...


Jim

[fecska]

I would implore you to build the JCM800 first before tackling something like an AFD100.  Like was mentioned earlier, there are all sorts of little things you will learn along the way that would help you with your dream build.  The JCM800 is a well traveled design, relatively simple layout, and will get you past the face palming you will inevitably be going through along the way (something we all have done and continue to do... ).  These will be priceless (and I do mean $$$$) bits of knowledge that will help you when you build your AFD.  Plus, if your country is craving for good tube amps, you could sell the JCM800 upon completion to help fund your dream build.  You may also find that with some tweaking and incorporation of some of your favorite AFD features, your custom boutique FECSKA800 will surpass anything the AFD can do and sound better to your ears.  Like PRR said, many times the sonic solution in manufacturing is the cheapest route, not necessarily the best sounding route.


So, MY advice is to forget the 5w solid state amp and build something that will annoy your neighbors!  Doug has everything you need here to build an 800.  Jump in, plan to make some mistakes, let the forum help you when needed, and have fun!  Oh, and by the way, if you are used to high voltage stuff - you know to keep one hand in your pocket when hot...


Jim

I found a great step by step tutorial by Metroamp!
I will build this with my own parts.

Any sugestions?

http://www.metroamp.com/downloads/100W_MV_INST_DOWNLOAD.pdf

[PetaLue]

You can't go for the Amplifier direct from this schematic. First you have the need to understand the basic Amplifier circuit. Then after as they have different features on the basis of their configuration, you have the need to understand that also. Once you learned the basic you can go for any amplifier as per your requirement.

[Willabe]

For me the AFD100 is special because the power scaling on it, so i can get great tones on low volume.

And I want a LOUD amp,

 

[Willabe]

as i have little 2-15W amps, and dont want to pay 2000$s for a tube amp, what I can make in optimal case from 5-600$, meanwhile have fun :)

Unless your a manufacturer who can buy parts in large lots to get the price break, or you get the expensive parts, PT/OT/choke/tubes/sockets/chassis/cabinet/speakers/filter caps...... for free somehow, you won't be able to build a 200w amp and that's without power scaling, for $500/$600.

I don't think Marshall could do it for that price. No way.

Makes no sense to build a 200w amp and then power scale it down to 'low volume for great tones'.

A 50w Marshall with a 4x12" speaker cab is plenty loud! Heck, even with a 2x12" cab 50w is plenty loud! And you can scale it down to play in ~mid to small size clubs that only need a 30w to 20w amp.

Look at Kevin O'Connor's Power Scaling web site. He sells Power Scaling kits that work great, with all the parts including any PC boards for them. 

[John]

I'm pretty sure fecska got it figured out sometime in the last year.