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Little Sweetie Forum amplifier project


henry4841
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Guys I sure appreciate all what are contributing to this project. As I have said multiple times this is for the forum to help beginners and not about me. There are some better builders of amplifiers on the site that are better than myself that I am envious of. I never actually thought I would build another tube amplifier but I have thought about doing this for a long time to get more involved. I sure do not need another tube amplifier. SS, I still like to play with some. 

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I took a look at my work I did this morning. It always helps when you finish a circuit to check, and recheck your work. You cannot do enough checking because time spent at this circuit checking and rechecking will save tons of time trying to find a problem later. Only 5 parts and some wiring on the pre circuit to check over and over again. I found one error on one tube circuit I made and corrected it along with tying the 3rd grid of the tube to the cathode as Maynard writes in the notes. Also sent the pot ground pins to my star ground on both channels with separate pieces of wire. Just the way I do it. My star ground is the long bare 14 gauge wire. Easy to see if you look at those yellow caps with one end of them going to that long wire, star ground. 

 

Remember the schematic PS section on the schematic you see is not the one I used. Mine is the stereo PS one Maynard made for stereo use. It is shown in this thread somewhere. 

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Got 6 more critters to connect and then fire up time. I am happy when I plug a new build up if I don't see smoke. Seriously if you use the light bulb current limiter every diy should make it will keep the smoke in the box on first plug in. If it burns bright you know you have a problem. A variac can be used, instead of light bulb, of which I have but most of the time I just use the lightbulb current limiter. https://www.youtube.com/watch?v=wRFRwOnLsZI

 

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I'm not trying to change the schematic or design, I apologize for some mod suggestions, it was only for people that build this and might want to tinker with it a bit. I'll hold off on that talk and stick to the original implementation.

 

Now for the power supply discussion, although people might be construing it as a "mod" and "different" from the schematic the conditions are quite clear on the schematic of having 200v across the 6Y6, plate to cathode. So I disagree with people saying the discussion is not part of the original design, the goal is to get the same operating point as Maynard got with his mono amps but with a stereo amp.

 

I know the transformer Henry got and I know the circuit and the 6Y6 operating point from the schematic. I'm only trying to help you achieve what was intended by Maynard in the circuit design. Going with a 560 for R10 will leave you with only 155v across the 6Y6 which is not the design. I also just added voltages for the driver tube to help builders know they made the circuit correctly by checking against the voltages on the schematic that I provided.

 

Sorry I won't try to help if that's what is wanted. I'm really not trying to change anything, I crunched the numbers and agreed a choke even with a Stereo unit probably won't lower the noise enough to warrant the change. It's a nice circuit, I just want people to get the most out of the design by getting the correct 200v across the 6Y6.

 

I'll bow out if that's what is wanted.

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22 minutes ago, henry4841 said:

Do like I am doing when you start building it teaching those who want to do some diy. With pictures of course while you build. 

 

Maybe in future projects I can do that but right now I am so swamped I'm sure Shakey and Westcoastdrums just want me to get them done ASAP and not waste time taking pictures and educating people.

 

I'll of course post gut shots soon but I can't do any in depth write ups at the moment, it wouldn't be fair to them to waste time. Of course my back's been out the past few days so I've been slowly tinkering but mostly just resting because I can't really move or walk at any reasonable pace. Getting old and abusing my body with sports and whatnot as a youth isn't fun.

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Hey guys we are nearing the finish line. This is the fun part for me is when you get to the audio circuits. There is no fun for me drilling and cutting the chassis. Too much like work. Building a power supply is some better but most all PS's have a similarity. I started this project more like a job just to tell how an old man has built a few tube amplifiers the last 10 years or so. But when you get to the audio circuits it is getting to be fun for me. Just to see if I can still build a working amplifier at 73 years old. Seeing if I can put 6 critters on the preamp socket in the right place again. It has been a few years since I built one.

 

I want you young guys to think of me as Grandpa. Young guys to me are those under 53. I was a young man and you were not born. I am sure your mama told you to be nice to Grandpa. I consider every one that has said something on this thread as a friend and I am not going to argue with you about some silly thing. My best friend who passed away 2 years ago was one that always had to be right when we disagreed on something. If we talked about something early in the morning and disagreed he would bombard me all day long with emails sometime with videos trying to prove he was right. Whether I thought he was right or not I did not say anymore most of the time. And if I still wanted to say I thought I may be right I would just say something in a nice way like "I still am not so sure." Why, because he was my best friend. I let him believe he was right when I may have knew he was wrong. No big deal. Let's not argue on this thread. There are other threads on this site where plenty of that goes on you can go to. Remember some teenager may be lurking and you would not want your son to see you being nasty in a public place.  

 

Enough of that lets get back to the build. Wiring the inputs is pretty straight forward if you just look hard at the schematic. RCA inputs to the potentiometer. The one thing you should know about the pot is the center pin is the one that goes to the amplifier part. If you wire the two outside pins wrong the pot will just work backwards. Looking at the back of the pot The left pin is ground. Center pin goes to amplifier. Right pin is where you connect the wire from the RCA jacks. You get the outside pins wrong the pot will work in reverse. 

 

Input power to the transformer is, at least the way I do it of the IEC connector is this way. The connections are this  https://electronics.stackexchange.com/questions/356180/iec-connector-pinouts.  I wire the hot pin to the fuse first then the switch then to the red transformer wire. Fuse before switch so that if the switch ever fails the fuse will blow. The ground pin goes directly to the chassis. It keeps you safe from electricity if you have a failure in the amplifier. With any amplifier that has a 3 ground plug. The neutral pin goes to the other wire of the transformer generally black. Then you go to the power supply you have built. 

 

There is no reason for you to be inside this amplifier when it is running 'hot' with this build. No adjustments need to be made. Keep your hand out of it with it plugged in. The most important lesson to be learned if one starts playing with other tube amplifiers building or working on them when they are hot is this KEEP ONE HAND IN POCKET. You will be safe if you do that. Electrons seek the least resistance and if they get loose they will go the the ground pin unless you make a connection through your body by having two hands touching at the same time sending the electrons through your body. With one hand if you touch something hot it will bite you but not do any serious harm. That is if you are relatively heathy. I suppose some old man that has one foot in the grave may get killed but healthy people are more likely to hurt themselves getting away from it. Much like being bit by a spark plug wire on your car. Been bit many times working on a car myself and a few times working on a receiver or amplifier. I have seen one old mechanic actually hold a spark plug wire in his hand with the motor running to show you the spark jumping around on his hand. Not me.

 

Just remember lets all be friends on this thread. You seldom see heated discussions to the Pass diyaudio forum like you often do here. Very rare. Maybe we can change that here by being friendly. You lurkers, if there are any, do not be afraid to say something here. The only stupid question is the one you do not ask. We all started somewhere. If I do not have an answer maybe someone else will. 

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To continue to encourage new builders to get their feet wet, you don't necessarily need to drill holes in a chassis to get started building a tube amp; you can "breadboard" a tube amp too, as shown below.

 

This allows you to quickly mount components and make/change connections. If wired correctly, you should not have any noise, but with a set-up like this, it is more about getting the circuit up and running. 

Breadboard Amp Example.jpg

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Henry's comment about getting "bit" reminded me of a story that has absolutely nothing to do with this thread, but I think some of you will relate.

 

I have a Buggera tube guitar amplifier that came through my house fire relatively unscathed. Somewhere along the line, though, it must have gotten banged around a little because when I fired it up, there was a pop and it died. New fuse...pop. Took it to a local store who farms the repair work out to the only guy in town who repairs tube amps. A couple of days later, I get a call that the amp is ready. When I picked it up, the guy at the music store said the repairman had told him the Buggeras are great little amps, but they are built on a PCB and he had received a rather potent shock as soon as he started working on it. I guess that might be a case for point-to-point wiring.

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1 hour ago, Curious_George said:

To continue to encourage new builders to get their feet wet, you don't necessarily need to drill holes in a chassis to get started building a tube amp; you can "breadboard" a tube amp too, as shown below.

 

This allows you to quickly mount components and make/change connections. If wired correctly, you should not have any noise, but with a set-up like this, it is more about getting the circuit up and running. 

Breadboard Amp Example.jpg

Love the blue tape wiring harnesses...😄

 

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When I was designing the power supply for my 211 amp (>1kVDC), I breadboarded it as in the picture. I was careless and got bit on the hand from my finger tip out through my palm. I survived (of course), but had a nasty little puncture hole in my palm. 

 

No shocks sense then! 

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Found this this morning poking around the webs:

 

"Ever wanted to build a highly dangerous, inefficient, yet awesomely retro piece of electronics? Well, I have. That's pretty much what a tube amp is. Vacuum tubes are old electronic components that act like transistors, controlling a lot of current with a little current. You usually hear about tubes being used in guitar amplifiers, because they distort in a way that suits guitar playing. However, tubes can also be used to amplify a stereo signal from another audio source such as a CD or MP3 player. Tube amps, unfortunately, aren't the most practical things in the world; they consume a great deal of power, get very hot, and are big. That being said, they look damn cool, and some people seem to think they sound pretty nice, too."

 

https://www.instructables.com/Building-A-Stereo-Tube-Amp/

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13 minutes ago, jjptkd said:

Vacuum tubes are old electronic components that act like transistors

 

Sheesh. I am old enough to remember when my father bought his first transistor amp. We looked at it like it was something that came out of a ship from Mars, and were amazed that it actually produced sound despite having no tubes.

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1 hour ago, CWelsh said:

Henry's comment about getting "bit" reminded me of a story that has absolutely nothing to do with this thread, but I think some of you will relate.

 

I have a Buggera tube guitar amplifier that came through my house fire relatively unscathed. Somewhere along the line, though, it must have gotten banged around a little because when I fired it up, there was a pop and it died. New fuse...pop. Took it to a local store who farms the repair work out to the only guy in town who repairs tube amps. A couple of days later, I get a call that the amp is ready. When I picked it up, the guy at the music store said the repairman had told him the Buggeras are great little amps, but they are built on a PCB and he had received a rather potent shock as soon as he started working on it. I guess that might be a case for point-to-point wiring.

Repairmen got pretty scarce when the throw away cheap TV and SS amplifiers made the scene. But they are making a comeback kinda with those expensive flat screen TV's and tube guitar amplifiers that many musicians love. Reason for tube guitar sales, musicians love their tone more so than driving them into distortion. Yes some of those hard rockers love to distort them when  playing but most just prefer the sound they make over a SS amplifier. 

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