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Little Sweetie Forum amplifier project


henry4841
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@henry4841 I moved this thread here while you build it. I removed (or tried to) all of the extraneous stuff, when it comes time to sell it I would suggest putting a single line ad in the Garage Sale section with a link to this thread. 

 

Let me know if you need anything else on this.

 

Travis 

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11 hours ago, henry4841 said:

Now I have an extra hole in the top that I wish was not there.

 

9 hours ago, mike stehr said:

 

They make nickel or chrome plated sink plugs/caps in smaller sizes.

You can cover the hole with one if so desired...you may have to enlarge the diameter of the hole to fit the cap being they only get so small. Or a dummy screw if you have clearance.

Use a really good looking bolt head and it will appear like it has a reason for being there. 😄

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10 hours ago, Travis In Austin said:

@henry4841 I moved this thread here while you build it. I removed (or tried to) all of the extraneous stuff, when it comes time to sell it I would suggest putting a single line ad in the Garage Sale section with a link to this thread. 

 

Let me know if you need anything else on this.

 

Travis 

Thanks, I honestly did not know where to put this thread and it be alright for those that control this forum. Moderators want peace and to be left alone doing more important things than being a referee on a social media forum. Threads get locked or deleted when individuals get to arguing over who is right on some silly subject with both afraid the other is going to have the last word. Let's not do it here on this thread. Let's all be friends and try and help a beginning teenager or young adult build his first amplifier. That is what we are, friends that disagree sometime. Friends first before being right. At 73 I have made enough enemies in my lifetime. I do not need any more.

 

This amplifier I am building is still spoken for so it may not appear in the For Sale section. A number of builders yesterday gave their opinions of how they would teach their kid where to put the RCA jacks and their reasons. Both ways work just fine and the way they like is surely going to look best when finished. It was just a suggestion of mine that a beginner may want to put the jacks close to the potentiometer. If they choose this way you want to turn the chassis around like in my SET 45 tube amplifier. Put the power supply transformer way back in the chassis along with the PS board I made. You want to keep them as far away as possible from the input of the first stage. A tiny bit of hum that enters the first stage that you can hardly hear is going to be amplified and made a lot worse when it gets to the second stage and out to the speakers.  I want more discussions like yesterday on this thread but keep it civil.

 

The more I look at this design of Maynard's the more I like it. Simple with a few parts. There is an ol' boy in California who is getting richer building circuits like this, simple circuits with two stages of amplification using transistors named Nelson Pass. The company is called Firstwatt. I have built, I believe, all of the FW design clones he has made public. The SE versions like this amplifier that I have built sound good, really good. Almost as good as this SET amplifier. 🙂 Not just this one but most any SET tube amplifier sounds slightly better. Some say what Nelson is trying to do is make a transistor amplifier sound like a tube amplifier. I once asked him on the other forum why he had not designed tube amplifiers. I think the main reason is more money to be made in SS. Larger market as well. He was quick to answer back on the forum "who said I do not own or have not designed tube circuits."  I bet he has a SET 300B tube amplifier with those original expensive Western Electric tubes he listens with on occasions.

 

This little amplifier of Maynard's is not one I would recommend for those using other speakers. Those ones that are 85db. Not that they would not sound good on them. My great, great grandfather probably listened to a console radio with a tube circuit much like this one with 1 watt and a 85db speaker. That is if he could afford one of those console radios, those things were expensive back in the day. A 5 watt amplifier back then was a big one. But for anyone with a horn midrange it is going to have more than enough power for most sensible listening individuals. Not going to have that deep strong bass like a mega watt SS amplifier but you will hear good bass with it. It is there. Add a sub and you have all you could want. Most of us that is. Perfect little amplifier for Klipsch speakers. Probably all their speakers even those that are not Heritage. Probably any speaker 95db or better which includes most all if not all of the Klipsch brand. 

 

If you want a visual image of me think bald, 20lbs overweight, 73 year old man in coveralls. Kinda like those hillbilly's on the TV show Moonshiners. I live in the flat part of Alabama but we call those folks in north Alabama hillbilly's. They have hills. Much the same though. Here where I live on my street we use the word ya'll. Thank the Lord for spell check or you would see how I am such a poor speller.

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I had planned for us electronic nerds and builders to discuss OPT's this morning. Specifically Edcor 10 watt SE ones and these Hammond ones I am using. The main reason I have always used Edcor's in my builds was they use to be much cheaper than the Hammonds but with a wait period for them to build them. Being a cheap diy'er I waited. Now with the price increase the Edcor's and the Hammonds are about the same price. The Edcor with those blue bell caps sure look better. Look like they are made for diy'er to put where they can be seen. The frequency response shown on data sheet is better but, a big but, they do not state at what wattage the freq response is measured at. They are good OPT's. At least I have always like the sound they make. Not so much the cheaper ones they sell. Just do not sound as good as the 10 watt ones. To my ears. I should mention both the Edcors and the Hammonds are quoted for guitar amplifiers. Now how does a OPT know what it is made for or called? There are those on the web that wind their own transformers. Just wire wrapped around an iron core. Why can you not take a OPT that is quoted for HiFi and not use it in a guitar amplifier or the other way as well. If it reproduces chords on a guitar at a certain frequency it is going to reproduce vocals and music for hifi use just as well within it's freq range. That's the way I see it.

 

Then we come to the one Maynard always has used and recommended to me. The Hammonds 125CSE ones. More pro looking. Look like they are made to be hid in a cabinet somewhere. And they are. The are sold by electronic warehouses that sell to business making and building tube amplifiers. They are actually a little cheaper now than the Edcor 10 watt ones. The price today is $60.07 and if a company that builds guitar amplifiers buys a 100 of them the price is $48.84 apiece. Frequency response looks poor for a hifi amplifier but you have to carefully read the spec sheet and you find that it is rated at maximum power 8 watts. In a guitar amplifier some rock musician will turn the amplifier wide open and start hitting some chords and expect the freq response to be what is stated on the spec sheet. Not something we HiFi music lovers are going to do. But if you turn down the wattage more to what a tube hifi amplifiers nominal power being used the numbers are actually better than the Edcors. At least George Anderson, a guy that knows his stuff, says on his website . He found the Hammonds at 1 watt to be 11.7Hz to 42.9KHz with 50mA use. Better at 70mA. The range of this amp and most EL34 family of amplifiers. Very respectable numbers. Beats Edcor. Who knows what wattage they are testing their OPT's at. We know one thing, they do not want to tell. 

 

My common sense tells me Hammonds should be better. One big reason is Maynard says they are good. Maynard knows his stuff when it comes to tubes. From what I know he has been doing tube repair and building most of his adult life. At least that is what I have found out knowing him for a number of years. Final judgement is going to be when I hear them but I am expecting as good and probably better than Edcors. The line of Hammond 125's goes bigger with the E, F, G versions. The one I am using for this build are the C versions. They have a line they call for HiFi use which are big and expensive. The smallest one of them is rated for 25 watts and cost $146.49 apiece. Way overkill for a SE 5 watt amplifier. But they are available for those that want the best. This thing of calling a OPT either for guitar or hifi is just BS in my opinion. Probably comes under the protect their a##. 

 

Anyway what are the ones following this thread think. Something we can discuss and talk about to pass the time and maybe enlighten a future amp builder.  

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Did not get a lot done this morning but I have started wiring up the PS transformer and made the AC connection of the secondary to the bridge rectifier of my PS board. When all this power wiring is done the amplifier part is the easiest and fastest. This transformer's secondary is actually two separate PS sections along with the heaters. This means if one wants he can make  two power supplies like a mono build with one PS transformer. Same with the heater section. Two heater sections. You could use one section for two tubes and the other section for the other two tubes. You would want one heater section to be for a pre and power tube. I am tying the two 200V sections together along with the heaters. When you do this you increase the amp rating with the same voltage. 

AS_1T200__27638.1387573636.1280.1280.jpg

P1030996.JPG

P1030997.JPG

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On 8/6/2022 at 4:48 PM, Shakeydeal said:


I hate to say it, but anyone averse to paying 500.00 for a custom amp should probably take up needle point instead…

Agree...

 Nice price...

Edited by billybob
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8 hours ago, henry4841 said:

 

If you want a visual image of me think bald, 20lbs overweight, 73 year old man in coveralls. 

Henry, it is unfortunate that we live so far apart.  We could sit on the porch of the general store reminiscing about the good ol’ days.  I am also a bald old timer, but 50# underweight.  A local farmer offered me a job as a human scarecrow.  If I had time, I would take him up on it!

 

Maynard

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Did you just parallel the two secondaries together and run them through a single bridge rectifier?

 

Personally I wouldn't do it that way since the two windings are probably slightly different.

 

The better way to do it is a center tapped full wave rectifier where you ground the two middle legs of the two windings (opposite phase of each other, one winding negative cycle and the other positive cycle). The other two legs pass through one forward biased diode each and then connect together for the B+. 

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There is one important thing I must do in the morning. Make the chassis ground also called earth ground. Very important for safeties sake. There are two grounds in the amplifier. The amplifier ground and chassis ground. You do not want any of amplifier grounds, the RCA inputs or pot terminals, to touch the chassis creating a ground loop. Check them with your ohmmeter to be sure they don't after installing them. At finishing the amplifier part of the build I usually connect the star ground, the only amplifier ground point, to the chassis ground with some resistance. not always necessary but sometimes helps. Just one wire with a resistor from star ground to chassis ground. 

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2 hours ago, captainbeefheart said:

Did you just parallel the two secondaries together and run them through a single bridge rectifier?

 

Personally I wouldn't do it that way since the two windings are probably slightly different.

 

The better way to do it is a center tapped full wave rectifier where you ground the two middle legs of the two windings (opposite phase of each other, one winding negative cycle and the other positive cycle). The other two legs pass through one forward biased diode each and then connect together for the B+. 

Another way to do it. 

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2 hours ago, henry4841 said:

You do not want any of amplifier grounds, the RCA inputs or pot terminals, to touch the chassis creating a ground loop.

 

IF the chassis connection say from an input connection is the only ground connection it may cause hum problems. Current always takes the lowest path of resistance so as long as you keep your local current loops short it doesn't really matter if the signal ground touches the chassis ground in power amplifiers. For example the input jack and first stage grid and cathode connections. The input jack can touch the chassis but make sure you connect a short wire from the ground tag on the input connector to where the first stage grid leak resistor and cathode resistors connect and the small signal currents will have a low resistance path to where they need to be and not travel through the chassis. I don't use a "star" ground system, I just use a bus ground and everything including the chassis connects to this. I get extremely low noise floors this way. You can get hum with star grounds, have seen it many times, so long as you understand each and every current loop and keep them short you won't have problem no matter how you do it, bus ground or "star" ground. I have on one end of the bus ground the rectifier and reservoir capacitor and on the other end of the bus is the input signal grounds. It's extremely quiet because each "local" current loop has a short return path back to it's source.

 

I know people find a ground "recipe" that works for them and stick with it but as long as you understand each and every current loop and keep them as short as possible they won't pollute each other even if they all connect to each other.

 

One way to get good at understanding this is to draw each and every current loop over the schematic. Use arrows for direction and different color highlighters to distinguish between signal vs DC currents. For instance the input signal loop goes between control grid and cathode of the first stage, the current flows through the grid leak resistor and also through the cathode resistor to the cathode, if the cathode resistor is AC bypassed with capacitor then the cathode resistor impedance can be ignored. The output signal current of that stage is between plate and cathode, it flows through the power supply filter capacitor to the cathode either through the cathode resistor or if AC bypassed through the cathode bypass capacitor to the cathode. They are two different AC current loops. That's also why they call it a common cathode gain stage, the cathode is common to both input and output current loops. The input is between grid and cathode, the output is between plate and cathode.

 

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Sitting in my backyard yesterday I got to thinking about that ol' boy Deckert of Decware. He has took a little amplifier such as this one and made a good business from selling it. Selling those little things as fast as he can make them. I see he also sells some Cadillacs too but he is selling a lot more Chevrolets. He is doing this with an old surplus Russian made for something else tube. The thing about the Russian 6P15 tube is if you tie 2 of those pins together you make a Russian 14 tube which is a substitute for the EL84. That 6P14 tube is now as expensive as a new production EL84 but you can still buy the 15 tube cheap. He now has a good source for the output tubes. He is also using a Russian 6P1 tube for the pre tube. Probably because of the price and hey it works alright. Someone has already posted in this thread he thinks it is possible to get 2 watts from this 6Y6 tube. Not that I think you need it with our speakers but saying 2 watts instead of 1 would make it sell better. Russian surplus tube or good ol' USA made for audio tube. Decide for yourself. Do not get me wrong. I have two amplifiers I have built with the 6P15 tube. One a clone of the Zen and the other a PP one. Both sound really good but to me the 6Y6 tube sounds better. The active device is what sound is all about whether tube or transistor. All those other parts of the amplifier are there to just make that active device work and sound best. Not to flavor the sound of the active device. In theory they sound be neutral as far as contributing to the sound and not add anything.

 

My personal Sweetie uses Nos RCA 6Y6's along with NOS Jan 6SJ7's. This one I am building for a build guide for a Area51 is going to have NOS Westinghouse 6Y6's along with some NOS 6SJ7's made in England tubes. I bet money they are NOS Mullard made. Those NOS Mullard tubes are like gold. I bought them for this build and this build they will go but I would sure like to have a pair of them for my personal Sweetie. And yes Area51 has already spoken for this amp. Even offered to send me the money already. I am going to wait to see if I can still build a good sounding tube amplifier before taking any money. Hey it has been 2 or 3 years since I have built one. We talked about a wood case and he agreed to pay an extra $100 for it. I see a guy on Ebay building wood cases for those old 70 receivers charging $300 and getting buyers. I think $100 is a fair price along with $100 for putting the parts together for the amplifier. If someone thinks I am making money they are in worse shape than me and I can feel sorry for them. I am just doing this for something constructive to do in my retirement years to have fun. That is the reason I am just taking my time building it. As much for fun for me as the guy who is getting it. At least I hope he likes it after he gets. I will not sell it if I do not like the sound it makes but I still think I am able to build it. At least today I do. 

 

That ol' Deckert is sure doing good for himself building a cheap no frills little amplifier. Some enterprising young man could do the same thing. Seems to be a market for such a little amp. Deckert got some colorful youtube guy to praise his amplifier and his sales have taken off. Wonder if he had to wine and dine him. Smart guy who has a made a good little business for himself. Lot easier turning out simple amplifiers for a profit, and a lot of them, than complicated builds with fewer sales. If the market is out there for them they will sale. I am too old to start doing such a thing. I like my simple life now at 73. But something for a young man to think about though. Good way to earn a few extra bucks every month. 

 

Maynard and I talked about doing something like this thread years ago. I have not built a tube amplifier in 2 or 3 years. The last year or so I have been buying some old not working receivers on Ebay and fixing and restoring them with new capacitors. So I am rusty along with getting older and more forgetful. Some of you guys with good eyes following this thread should have said something about that earth ground. Like hey Henry do not forget to run a wire from the center pin of the IEC to the chassis. I might need some more help on this build guide along the way. Keep your eyes open for me and when I post a picture but please do it in a constructive way and not try and hurt my feelings. Remember I am just an old man. Treat me like your Grandfather. Be easy on me. 

 

Captain is the only one who has spoken of a different way of wiring the transformer. Smart guys find better ways of doing things and Captain seems to be a smart guy. But I am going to keep this build simple using the KISS system. I am teaching my grandson to build his first amplifier (not actually) and I think it easier to tell him to tie the two white wires of the PS transformer together and do the same with the two yellow wires and then attach them to the center pins of the bridge rectifier. After all we just want to turn AC to DC using the bridge rectifier. After filtering the DC through our CRCL, the output transformer is our L, network for the 6Y6 and through a CRCRC network for the 6SJ7 I think it the DC will be plenty good enough. At least it is with my personal Sweetie. The bridge rectifier has four pins one marked + then two pins marked with little ss' for the AC lines of the transformer to attach to, then a - pin.

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A little rambling about tubes. The coating of the cathode in the tube is what separates a good tube from a not so good one. Something the old maker of tubes did so well. What makes Western Electric tubes so sought after and highly prized. It was their highly guarded secrete sauce they perfected back in the day when tubes ruled. The late Roger Modjeski said he once went to a European country that made what he thought was excellent sounding tubes. He saw the vat they mixed the ingredients in and they let it sit overnight every time. He said he did not know what was in the vat that made the tubes sound so good. He said it could have been the janitor urinating in the vat overnight that made them sound good.  This was said in his lecture at a Burning Amp Festival held yearly. Made me laugh. 

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10 hours ago, captainbeefheart said:

I just use a bus ground and everything including the chassis connects to this. I get extremely low noise floors this way.

 

I have on one end of the bus ground the rectifier and reservoir capacitor and on the other end of the bus is the input signal grounds. It's extremely quiet because each "local" current loop has a short return path back to it's source.

 

I know people find a ground "recipe" that works for them and stick with it but as long as you understand each and every current loop and keep them as short as possible they won't pollute each other even if they all connect to each other.

My recipe is a ground bus too. It's something I've done for 20 years and always yields excellent results. I use the solid copper ground conductor (or strip the black/white conductor) from a length of 14/2 household wiring for my ground bus and route this through the amp. One end terminates at the power supply capacitors, the other end at the RCA inputs.

 

I always ensure my RCA's are isolated/insulated and do not ground to the chassis when mounted. The RCA's are connected to the ground bus at one end. I also connect the chassis (earth) ground to the RCA end of the ground bus through the below circuit to keep the signal ground and earth ground paths separate. The essentially turns your metal chassis into a big shield to keep EMI/RFI out of your circuit, which is why I like a full metal chassis. 

 

The ground bus is connected to the amp circuitry as the Captain said; power supply caps at one end (since this end of the bus has the most ripple) then subsequently less "ripple sections" attached to the bus toward the RCA end of the bus. 

 

An X or Y safety cap can be used or a mylar one as well. I came across a bunch of X caps for free and I use them. 

Earth_Signal Ground Scheme_010619.jpg

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A little progress. Here is the schematic and how I work off of one. I have installed the 390K resistor to pin 6 of the 6J tube and use a highlight to mark what I have done. I do both channels now but when first started building I printed out two schematic sheets and did one channel at a time. I hope I am finished with the PS board because I have made the necessary connections to it and fastened it down. Installed the safety cap and made a chassis ground. All for today. Slow and old. That little component tester is really neat and cheap. I have more costly one none any better actually. Amazon,  The scan did not work as I wanted it to. One will have to download it to see what I am talking about. 

P1030998.JPG

P1030999.JPG

Scan1.PDF

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Since Henry mentioned Deckert’s Zen Triode, prospective builders of their first tube amp may enjoy watching Deckert actually build one.  Be sure to watch all 12 videos.  Seeing a point to point build in real time gives a somewhat different perspective from seeing still photos.

 

https://www.youtube.com/watch?v=n1ENOdYN6iA

 

Henry, if you think this will dilute the thread, I will delete it.  Let me know.

 

Maynard

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On 8/17/2022 at 10:56 AM, henry4841 said:

Did not get a lot done this morning but I have started wiring up the PS transformer and made the AC connection of the secondary to the bridge rectifier of my PS board. When all this power wiring is done the amplifier part is the easiest and fastest. This transformer's secondary is actually two separate PS sections along with the heaters. This means if one wants he can make  two power supplies like a mono build with one PS transformer. Same with the heater section. Two heater sections. You could use one section for two tubes and the other section for the other two tubes. You would want one heater section to be for a pre and power tube. I am tying the two 200V sections together along with the heaters. When you do this you increase the amp rating with the same voltage. 

AS_1T200__27638.1387573636.1280.1280.jpg

P1030996.JPG

P1030997.JPG

 

I just saw this and you may have discussed it already, so forgive me if you have and you already know this...

 

If you mount your toroidal transformer down with a bolt, like I suspect you do, make certain there is adequate clearance from the bolt to the lid.

 

The reason is that the bolt and case will form a single winding on the transformer all by themselves, and you'll pull your hair out trying to find out why the fuse keeps popping when you have the lid on but runs fine with the lid off.

 

Ask me how I know this.

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