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Little Sweetie Forum amplifier project


henry4841
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45 minutes ago, CWelsh said:

Here is an initial draft of a parts list for the Little Sweetie. @henry4841 and I are going back and forth checking details as time allows. I downloaded Henry's Mouser order form to produce the core of the list, so I think some of the quantities may reflect orders for "stock" rather than actual requirements for the project. We will get those details cleaned up before we publish a final version.

 

Please be encouraged to review the list for errors and omissions. I will welcome suggestions for edits and/or formatting that will make it better for new builders. I expect to do some clean up on descriptions as well.

 

Thanks in advance!

Little_Sweetie_Parts_List_V2.xlsx 8.69 kB · 0 downloads

When Mr. Welsch refers to may be stock I think he is referring to my ordering a 1$ or more of resistors just in case. Happened on my build when I broke the leads off of one resistor. If I did not order extra you may have to pay $10 shipping for a 10c part. Just the way I do it. Check Maynards parts list on the schematic and order just what you need if one wants to be precise.

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34 minutes ago, CWelsh said:

Here is an initial draft of a parts list for the Little Sweetie. @henry4841 and I are going back and forth checking details as time allows. I downloaded Henry's Mouser order form to produce the core of the list, so I think some of the quantities may reflect orders for "stock" rather than actual requirements for the project. We will get those details cleaned up before we publish a final version.

 

Please be encouraged to review the list for errors and omissions. I will welcome suggestions for edits and/or formatting that will make it better for new builders. I expect to do some clean up on descriptions as well.

 

Thanks in advance!

Little_Sweetie_Parts_List_V2.xlsx 8.69 kB · 0 downloads

I would add a price column just as a reference. Just so a builder knows how much an item would cost. Plus, in 20 years, we can look back and say "wow, in 2022, parts we so cheap!". 

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It's alive. Cannot tell a lie, it did not happen without some burps. I will never claim to be a pro amp builder. Not surprising being it has been a few years since I built a tube amplifier point to point. Having a problem is good. You can learn a lot more that way about electronics. Maynard was a big help for me when I first started building 10 years or so back. There are more on this forum that will do the same with you a beginner.

 

I did work work on it live, makes it easier to find problem, but could be found almost as easy by just checking the parts with multimeter and all the connections to be sure they are correct with schematic. I am going to have to attach star ground to chassis ground probably through a 100ohm resistor. Hummed real bad until I did that during testing. Right now I am just going to call it a day and start again tomorrow. Too much stress for an old man documenting a build and worrying about him not able to produce and get it to work. 🙂  This kind of detailing a build from start to finish is best left to some young talented youngster. Remember youngster to me is under 53 years old. The second picture shows it still chained to the dim bulb tester with it running. If it were burning bright you have a dead short somewhere. I will turn it loose from it's chain and do some testing tomorrow but it sounds really good with some 85db test speakers. 

 

 

P1040008.JPG

P1040009.JPG

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37 minutes ago, Curious_George said:

I would add a price column just as a reference. Just so a builder knows how much an item would cost. Plus, in 20 years, we can look back and say "wow, in 2022, parts we so cheap!". 

 

I can do that. The prices were on the Mouser order, of course, but I stripped them out thinking they probably won't be accurate when someone wants to order, but I agree that someone might be shocked at the "bargain" prices of 2022...LOL

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2 hours ago, henry4841 said:

It's alive. Cannot tell a lie, it did not happen without some burps. I will never claim to be a pro amp builder. Not surprising being it has been a few years since I built a tube amplifier point to point. Having a problem is good. You can learn a lot more that way about electronics. Maynard was a big help for me when I first started building 10 years or so back. There are more on this forum that will do the same with you a beginner.

 

I did work work on it live, makes it easier to find problem, but could be found almost as easy by just checking the parts with multimeter and all the connections to be sure they are correct with schematic. I am going to have to attach star ground to chassis ground probably through a 100ohm resistor. Hummed real bad until I did that during testing. Right now I am just going to call it a day and start again tomorrow. Too much stress for an old man documenting a build and worrying about him not able to produce and get it to work. 🙂  This kind of detailing a build from start to finish is best left to some young talented youngster. Remember youngster to me is under 53 years old. The second picture shows it still chained to the dim bulb tester with it running. If it were burning bright you have a dead short somewhere. I will turn it loose from it's chain and do some testing tomorrow but it sounds really good with some 85db test speakers. 

 

 

P1040008.JPG

P1040009.JPG

For those not familiar with the "Bulb Tester", it should be made with an incandescent type bulb (100W). I've never tried a newer LED type bulb, but it may work. A CFL (curly cue) will not work in this capacity. 

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I see Mike Stehr liked my last post. He is another guy, I could not remember his name a few days ago, that I like his builds on this forum. On the same level as Maynard's builds. Real professional looking. 

 

I got to thinking why you have an awful hum without tying the amplifier ground to chassis ground. This build uses a shielded transformer with a green ground wire that should go to chassis ground for safety reasons. Having two ground points in your amplifier is more than likely going to cause ground loops, hum. Just as soon as I attached a test wire from star ground to the chassis ground the hum and noise died, nothing. I think I am just going to attach the star ground directly to chassis ground minus a resistor on this amplifier. I looked at my Sweetie and that is what I did when it was built years ago. Maynard installed an AC cap, called safety cap, on the input AC that should take care of any noise coming in from there. Most of those upright other power transformers do not have a ground wire on them that you attach to chassis ground. Not shielded. 

 

The other builders participating on this thread were a lot help with this project. George caught where I did not attach a ground point like Maynard's schematic. And Captain made a schematic with the voltages at different points in the build which I used yesterday morning finding the problems I had. I bet he has one of those electronic calculators I do not want to even touch. My thing is to get an old audio receiver or amplifier as not working and see if I can fix it.

 

The problems I had were a direct result of not doing what I said I was going to do a couple of days ago. Stop and sleep on it and then check my work in the morning before firing it up for the first time. I did not do what I said I was going to do so I had to do the checking after I first tried to fire it up. Probably cost more time and sure made it more frustrating not following my directions. Like woodworking where you measure twice and cut once kind of thing. I plan on tidying up some wires and doing some testing this morning to make sure the sine wave looks good then listen with it on my horns to see how it sounds for a few days. Put a few hours on it just to make sure it will not have any problems for a few years, hopefully a decade or more. I would like to put 6 or 8 hours on it just to be sure and I usually only listen to music a couple of hours if that a day. I am thinking the first of next week before I am ready to ship it to Area51. That is if he still wants it. This is if no problems show their ugly head. 

 

 

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2 hours ago, henry4841 said:

I got to thinking why you have an awful hum without tying the amplifier ground to chassis ground. This build uses a shielded transformer with a green ground wire that should go to chassis ground for safety reasons. Having two ground points in your amplifier is more than likely going to cause ground loops, hum. Just as soon as I attached a test wire from star ground to the chassis ground the hum and noise died, nothing. I think I am just going to attach the star ground directly to chassis ground minus a resistor on this amplifier. I looked at my Sweetie and that is what I did when it was built years ago. Maynard installed an AC cap, called safety cap, on the input AC that should take care of any noise coming in from there. Most of those upright other power transformers do not have a ground wire on them that you attach to chassis ground. Not shielded. 

 

 

Even in (most) equipment that only has a 2-prong plug, the chassis is grounded to signal ground through a 0.1uf cap. Sometimes there is a "lift" switch for this. This allows the chassis to act as a shield (EMI/RFI) for the internal circuitry. 

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24 minutes ago, henry4841 said:

I think I have found what I am going to cover that extra hole on the top of the case with. What do ya'll think? An old, I think copper, Mexican coin my Dad brought back from Mexico 50 years ago. I have a sack full of them. 

 

 

P1040010.JPG

Great idea! You can call the amp "corazón de la música". The heart of music.

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Spent the morning with the intention of testing this amplifier with signal generator and scope. Hooked up everything correctly and no signal on one channel. Started taking voltage readings, injecting signals on grids still one channel dead or at least very weak. I could swear both channels were playing music yesterday when I quit. Decided just to send some music into the thing and guess what, both channels sounding really good like yesterday. One channel on my Chinese signal generator is bad. Am I the only one things like this happen to? Amp good, signal generator bad. I have another one to use in the house but it still sucks. That is two signal generators I have had problems with the last few years. 

 

Hooked up the star ground to chassis ground and installed a .1ohm 3 watt resistor for R14 instead of the .4ohm one it replaced. The .4ohm dropped the voltage too much. Maynard says .3ohm but I did not have one of them. With the .1ohm resistor the filament voltage is 6.25V which is perfect in my book. Maynard is the only designer I have built an amplifier from that likes to drop the filament voltage some for longer tube life. Most just install the wires from the transformer directly to the heaters.  

 

At least for now all is good. Still need to tidy up the wiring, zip ties, install some plastic stick on terminals to hold some wires etc. Feel like the morning wasted and it was as far as finishing the amp. At least I found out I have another bad signal generator. One channel on the thing does still work and I have a spare. 

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In action on top of a test chassis for FW clones. I like to test FW boards before shelling out money for expensive hardware to see if I like the sound first. Need to pick out knob but for now volume wide open controlled by my FW B1 buffer pre with sub outs. Dead quite on my horns with volume wide open and sounds just like what I am used to with my Sweetie. Really good to my ears but who can say what another person hears or likes. I like it. 

P1040012.JPG

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18 minutes ago, henry4841 said:

In action on top of a test chassis for FW clones. I like to test FW boards before shelling out money for expensive hardware to see if I like the sound first. Need to pick out knob but for now volume wide open controlled by my FW B1 buffer pre with sub outs. Dead quite on my horns with volume wide open and sounds just like what I am used to with my Sweetie. Really good to my ears but who can say what another person hears or likes. I like it. 

P1040012.JPG

Looks great Henry!

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On 8/19/2022 at 2:50 PM, Curious_George said:

My Musical Power Supply output transformers have shipped out. I should have them Monday. That was a quick lead-time. I can't wait to test them. 

 

I ordered the OT10SE-HF (HiFi version).

The Musical Power Supply Transformers came in; OT10SE-HF 5k/8 Ohm, 50mA

 

Preliminary testing shows that they are a good transformer when used within their parameters.

 

I tested them on a 2A3 amp biased at 55mA although 50mA is the max that Matt @ Musical Power Supply said they were designed for. More current through them will reduce the low frequency performance. 

 

1 Watt: 40Hz @ 10% THD+N

Bandwidth: 16Hz ~ 38kHz, -3dB

Mid-band distortion (1kHz): 0.5% THD+N

 

3.5 Watt: 45Hz @ 10% THD+N

Bandwidth: 20Hz ~ 38kHz, -3dB

Mid-band distortion (1kHz): 5% THD+N

 

These transformers should be good for any project that calls for 50mA or less in the output stage. 

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On 8/21/2022 at 5:44 AM, 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. 

Look Mom! No clip-leads! ;)

 

If one wants to breadboard amplifier circuits of lower voltage/current, (like quite a few of Maynard's circuits) a guy can pick up a Tube DC power supply to use to power up an amplifier circuit.

 

Then one doesn't necessarily have to buy PS iron or PS components. You just set-up the board and lash up the heater supply and B+. 6.3 volts at 4 amps is plenty of current for a few common tubes.

 

Unfortunately, the Heathkit PS-4 and other similar Heathkit power supplies are only good up to 400 volts at 100 milliamps. I have a Lambda tube PS that's only 300-350 volts, with current at 150-200 milliamps.

I wish I had a tube supply at 600 volts with over 200 milliamps current, but they are probably hard to find and very expensive in this day in age.

 

Even these lowly Heathkit power supplies are going for stupid money now.

 

 

DSCN3988.JPG

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13 hours ago, Curious_George said:

The Musical Power Supply Transformers came in; OT10SE-HF 5k/8 Ohm, 50mA

 

Preliminary testing shows that they are a good transformer when used within their parameters.

 

I tested them on a 2A3 amp biased at 55mA although 50mA is the max that Matt @ Musical Power Supply said they were designed for. More current through them will reduce the low frequency performance. 

 

1 Watt: 40Hz @ 10% THD+N

Bandwidth: 16Hz ~ 38kHz, -3dB

Mid-band distortion (1kHz): 0.5% THD+N

 

3.5 Watt: 45Hz @ 10% THD+N

Bandwidth: 20Hz ~ 38kHz, -3dB

Mid-band distortion (1kHz): 5% THD+N

 

These transformers should be good for any project that calls for 50mA or less in the output stage. 

I was going to ask you this morning when you first get them to tell me in the country boy way. How they look, feel, compare in weight, size to the Edcor 10 watt ones we have been using. But you have already gone to work on them. Good job. 

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When us hobbyist geeks look at the Sweetie we just built we see an electron flow controller. What consumers call an amplifier. What the study of electronics is, is the control of the flow of electrons. If the electron is not flowing it does us no good. The really, really, really big guys play with the neutrons and protons. We play with the electron. There is a river of AC flowing electrons coming in our house from the power co. We take a stream of those electrons from the river and channel them into the bridge rectifier which will turn the AC electron flow into a DC electron flow which we can use to make the tubes work. When the DC electron flow comes out of the Bridge rectifier it is a bumpy DC electron flow and we use the capacitors and resistors in the PS circuit to make the DC straight or rather straighter. Straight enough to be used by the tubes. Then we funnel a smaller DC electron flow and channel it through the tube. As much as we can and still keep the tube safe and give it long life. This is our DC electron flow we have created in our tube. Into this DC electron flow we inject a tiny audio AC electron flow into the larger DC electron flow we made inside the tube which will come out of the tube amplified. Out of the first tube we then have a DC electron flow along with the amplified audio AC electron flow. Both can live together inside a wire. We want to discard the DC electron flow and only send the audio AC electron flow to the next tube. A capacitor does this job for us. It stops the DC electron flow and lets the audio electron flow through to the next tube that will do the same thing as the first tube coming out of that tube with enough force and power to move a speaker in and out. 

 

I hope this make sense. This is the way a old wore out country boy sees it. All this was learned by me watching too many youtube videos and reading too many articles posted on the web. At least I hope I got it somewhat right. Forgive the grammar errors made by an uneducated country boy. These days with the net a country boy can find videos of college electronic teachers teaching electronics to their students. Things I did not have when I first started wanting to learn electronics as a youth. You can learn a lot about electronics and circuits just sitting at home if you are interested in the hobby of electronics. I think of most of us on this forum are hobbyist with a sprinkling of electronic engineers. Most are just electronic geeks like myself playing with electrons to have fun. 

 

I like this simple little class A amplifier because I think I can understand a little about what is going on inside it. In class A we try and keep the audio signal as pure as it went in only being amplified by the circuits. In A/B amplifiers the audio signal is split in half with one tube amplifying one half and another tube amplifying the other half then trying to put the two halves of the audio signal back together again as best one can. At least in a push pull A/B amplifier.. Hey they have made it work pretty successfully. A well made PP A/B amplifier can sound really good but it is still not class A where we try and keep the audio signal as pure as we can. I have tried to learn some about class D but I really do not fully understand that form of amplification. From what I have found it is linear and not digital amplification but it is still not class A. 

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