I am very happy to report that after having to set this project aside since my last post in March 2024, I have finally been able to resume.
The next step was to have SendCutSend make a new top plate for me to accomodate all of the new holes required. I had them make it out of steel with matte black powdercoat for durability. I had to enlarge my front screw holes a tiny bit, but everything fits perfectly including the PCBs and the tube sockets. That's a relief! The cost was $56 including tax and shipping, and I considered that quite reasonable. Now I have to figure out how to open up all of the areas in the chassis (the silver areas below) to match the holes in the new top plate. I'm not quite sure how to do that, but I envision a lot of drilling and hand filing. I want it to be neat and clean. As you can see, I am again leaving out the magic eye tubes so there are no holes there. I just don't want them.
The top plate openings for the new transformers are perfect. Custom power transformer by Musical Power Supplies to work correctly on USA voltage. The massive output transformers came from Primary Windings in England. They are bigger than needed, but that's what he sells.
My next step is to open up all of the holes in the chassis to match the top plate, then paint the chassis and transformer bells matte black. I forgot that I already bought a miniature stepped attenuator for volume, so that was nice to find in my parts box. Now I need to order all top-quality parts to populate the PCBs and six top quality tube sockets.
The next step was to have SendCutSend make a new top plate for me to accomodate all of the new holes required. I had them make it out of steel with matte black powdercoat for durability. I had to enlarge my front screw holes a tiny bit, but everything fits perfectly including the PCBs and the tube sockets. That's a relief! The cost was $56 including tax and shipping, and I considered that quite reasonable. Now I have to figure out how to open up all of the areas in the chassis (the silver areas below) to match the holes in the new top plate. I'm not quite sure how to do that, but I envision a lot of drilling and hand filing. I want it to be neat and clean. As you can see, I am again leaving out the magic eye tubes so there are no holes there. I just don't want them.
The top plate openings for the new transformers are perfect. Custom power transformer by Musical Power Supplies to work correctly on USA voltage. The massive output transformers came from Primary Windings in England. They are bigger than needed, but that's what he sells.
My next step is to open up all of the holes in the chassis to match the top plate, then paint the chassis and transformer bells matte black. I forgot that I already bought a miniature stepped attenuator for volume, so that was nice to find in my parts box. Now I need to order all top-quality parts to populate the PCBs and six top quality tube sockets.
Pay attention to the orientation of the transformers, relative to each other.
This is also why it is useful to do a "dry run" assembly before choosing the final assembly.
This is also why it is useful to do a "dry run" assembly before choosing the final assembly.
Reference materials: RE transformers and magnetic field orientations. This is why a nearby transformer with a coil wound at a 90 degree angle relative to another transformer's coil will not induce a voltage (hum) in the other transformer.
Magnetic field orientation is relative to the coil, not the laminations.
Original design has identical coil orientations, with vertical coils on OPTs and horizontal coil on power transformer, laminations in the same directions are ok because they are not the controlling factor. I specified the transformers that I bought to be oriented this same way because it works. I just shifted the power transformer to the middle of the chassis instead of the back.
Original layout built per the kit, unmodified:
Magnetic field orientation is relative to the coil, not the laminations.
Original design has identical coil orientations, with vertical coils on OPTs and horizontal coil on power transformer, laminations in the same directions are ok because they are not the controlling factor. I specified the transformers that I bought to be oriented this same way because it works. I just shifted the power transformer to the middle of the chassis instead of the back.
Original layout built per the kit, unmodified:
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What is the purpose of the big black resistor in series with one of PT windings? The voltage was too high?
There's quite a nice relevant demonstration in this 3 minute YT video called "Transformer Orientation" by DeepBlueHarp.
Simon
Fully agree with @Never Get Old , but as well I understand that with end-bells on, @huggygood comment was reasonable.
Even with no end bells, and despite his extensive knowledge, XrayTonyB in his YouTube video build series of this kit a few years ago made the same mistake. He went to a lot of effort to rotate the transformers because he followed the laminations, not the coils. Someone way down in the comments section under the video pointed out that his extra effort did not accomplish anything, but by then it was too late.
Speaking of end bells, I removed the bells from one of the OPTs yesterday so I can begin painting, and it looks like Primary Windings makes a high quality product inside. The smell of fresh varnish was extremely strong for the first 2 months or so when I got them last year, but they look well made inside. I wish they had a smaller 15-18 watt model, but they only offer 10 watt and 25 watt models unless they do a custom design. The 25 watt models barely fit on the narrow chassis, but barely is good enough. It turns out that the end bells are bulkier than they need to be, which makes them take up more space. The power transformer turned out to be a lot smaller than expected. Apparently it is made with higher quality steel and is a more efficient design than the one that comes with the kit. It also ought to put out the correct voltages with no adjustments required.
Yes. The power transformer that comes in these kits from China is designed for 110 volts, which is fine in many other countries but not here. Even the newer ones that are labeled 115 volts are still actually 110. USA voltage is 121 volts where I live. So that resistor is to drop the voltage to the 6N1 driver tube filaments just enough to keep them in proper range. In the power supply, I had to also change the 100 Ohm in the C-R-C filter to 200 ohm to get proper voltages. The original build thread is here: 6P14P/EL84 Kit Building. With those adjustments I ended up with perfect voltages, despite the 110V transformer, and without having to use a bucking transformer or 100V supply, and it works perfectly.
The other two resistors you see there are a "virtual center tap" on the filaments for the output tubes. Many people miss those because they are not included in the kit, and without reading the direction manual that I translated (https://drive.google.com/file/d/1e6C1yM-10nynSAAbiULZAbfQxw6WqdfS/view?usp=drive_link) some people would never know because they only receive a schematic, which does not show them, and not the full 67 page direction manual that does show them. Those who do get the manual get it in Chinese, so I did a public service and translated it to English. Anyone who wants a copy, please download it because sometimes the Google link quits working.
I do not enjoy metal work, but it seems that the next few evenings will be spent with a drill and a file in hand as I open up all of the holes needed in the chassis. I'm eager to get this project going again after a 10 month pause due to life events.
I'm not sure what to use for tube sockets. The "premium" ones that came with my Dynakit ST-35 kit last year have such a tight death grip on the tubes that one day they will crack the circuit boards. Efforts to loosen them up failed. I don't want those sockets again. I think they are Belton.
Speaking of end bells, I removed the bells from one of the OPTs yesterday so I can begin painting, and it looks like Primary Windings makes a high quality product inside. The smell of fresh varnish was extremely strong for the first 2 months or so when I got them last year, but they look well made inside. I wish they had a smaller 15-18 watt model, but they only offer 10 watt and 25 watt models unless they do a custom design. The 25 watt models barely fit on the narrow chassis, but barely is good enough. It turns out that the end bells are bulkier than they need to be, which makes them take up more space. The power transformer turned out to be a lot smaller than expected. Apparently it is made with higher quality steel and is a more efficient design than the one that comes with the kit. It also ought to put out the correct voltages with no adjustments required.
Yes. The power transformer that comes in these kits from China is designed for 110 volts, which is fine in many other countries but not here. Even the newer ones that are labeled 115 volts are still actually 110. USA voltage is 121 volts where I live. So that resistor is to drop the voltage to the 6N1 driver tube filaments just enough to keep them in proper range. In the power supply, I had to also change the 100 Ohm in the C-R-C filter to 200 ohm to get proper voltages. The original build thread is here: 6P14P/EL84 Kit Building. With those adjustments I ended up with perfect voltages, despite the 110V transformer, and without having to use a bucking transformer or 100V supply, and it works perfectly.
The other two resistors you see there are a "virtual center tap" on the filaments for the output tubes. Many people miss those because they are not included in the kit, and without reading the direction manual that I translated (https://drive.google.com/file/d/1e6C1yM-10nynSAAbiULZAbfQxw6WqdfS/view?usp=drive_link) some people would never know because they only receive a schematic, which does not show them, and not the full 67 page direction manual that does show them. Those who do get the manual get it in Chinese, so I did a public service and translated it to English. Anyone who wants a copy, please download it because sometimes the Google link quits working.
I do not enjoy metal work, but it seems that the next few evenings will be spent with a drill and a file in hand as I open up all of the holes needed in the chassis. I'm eager to get this project going again after a 10 month pause due to life events.
I'm not sure what to use for tube sockets. The "premium" ones that came with my Dynakit ST-35 kit last year have such a tight death grip on the tubes that one day they will crack the circuit boards. Efforts to loosen them up failed. I don't want those sockets again. I think they are Belton.
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I like that, but I wish he had done a better job explaining the magnetic fields involved, especially why his "better" option is not ideal.
I'm not good at rotating objects in 3D in my head. Maybe this drawing will help someone in the future. I have tried to show the situations where the magnetic field lines would run parallel with the core of the OPT. My drawing skills aren't great, but this should be adequate. If anyone sees something obviously wrong, let me know so I can fix the drawing. This amplifier uses layout #5. That's the way the original kit was laid out, so I kept it that way when I ordered the transformers.
Great what you are doing here. I've been doing a lot of metal work lately on a couple of large mono block amps.
In case you don't know (you probably do) these are invaluable for tweaking holes to the perfect size:
https://www.amazon.com/Performance-Tool-W2967-Tapered-Reamer/dp/B073XVRG74/ref=sr_1_6?crid=2XFI4SP1UUS2D&dib=eyJ2IjoiMSJ9.k3kIFsATYyQ7xW7IYnzlbGQb45QQQ5bvxOrCeItYR5MqpyND9pdMrZO88snGbTw9OA8iGsTyhELXHPDyZzsv9j2oT-l_IKwNmG3DamhOU_saD5MbJn4MYv3BY9boXgL-zjk-3MXQ9sxGikMwQSz9KD2kXs_xuwiSiooFlB9e7KiJ9C5VdVAWIVuEtwA8sXBTPogbaRdG_1tN17e6vueqfLXiSU_bzseyC-U8YUUCN334ZA2ZhRiSl7OQi_8BVpfz_-uQivA-BPmHq-HyfE1pMUzTiGmaNZquJaAFaAngbNpq7U35QxiOk53nIkvu_MdSeArkYDEnSg9BVTglqO3VKJkvrdtb3U-Sv6j_7vkg-_4SlCKgT2sydQ6tatxkcU4mMS_44k5wgutGA3EylE5--zIrg6oSqmycCEQ72OAzMqpvqnxRlbBiFjHtsu9hWUY2.QgsAKglQU_XLC0NQBUnRB20Lj3GniVYRwN4kMv-HiKc&dib_tag=se&keywords=metal+reamer&qid=1736691757&sprefix=metal+reamer,aps,120&sr=8-6&th=1
Sorry for the stupidly long URL
In case you don't know (you probably do) these are invaluable for tweaking holes to the perfect size:
https://www.amazon.com/Performance-Tool-W2967-Tapered-Reamer/dp/B073XVRG74/ref=sr_1_6?crid=2XFI4SP1UUS2D&dib=eyJ2IjoiMSJ9.k3kIFsATYyQ7xW7IYnzlbGQb45QQQ5bvxOrCeItYR5MqpyND9pdMrZO88snGbTw9OA8iGsTyhELXHPDyZzsv9j2oT-l_IKwNmG3DamhOU_saD5MbJn4MYv3BY9boXgL-zjk-3MXQ9sxGikMwQSz9KD2kXs_xuwiSiooFlB9e7KiJ9C5VdVAWIVuEtwA8sXBTPogbaRdG_1tN17e6vueqfLXiSU_bzseyC-U8YUUCN334ZA2ZhRiSl7OQi_8BVpfz_-uQivA-BPmHq-HyfE1pMUzTiGmaNZquJaAFaAngbNpq7U35QxiOk53nIkvu_MdSeArkYDEnSg9BVTglqO3VKJkvrdtb3U-Sv6j_7vkg-_4SlCKgT2sydQ6tatxkcU4mMS_44k5wgutGA3EylE5--zIrg6oSqmycCEQ72OAzMqpvqnxRlbBiFjHtsu9hWUY2.QgsAKglQU_XLC0NQBUnRB20Lj3GniVYRwN4kMv-HiKc&dib_tag=se&keywords=metal+reamer&qid=1736691757&sprefix=metal+reamer,aps,120&sr=8-6&th=1
Sorry for the stupidly long URL
you can Insert a Link with that little icon that looks like 2 links of chain.
You also can eliminate everything from the question mark forward, which is all tracking information:
https://www.amazon.com/Performance-Tool-W2967-Tapered-Reamer/dp/B073XVRG74/ref=sr_1_6
Or use the insert link icon
Tapered Reamer Set
That's one of those tools that I should have bought decades ago. Seems I'm always drilling a hole in metal or plastic and needing to clean up the edges or enlarge it a bit.
https://www.amazon.com/Performance-Tool-W2967-Tapered-Reamer/dp/B073XVRG74/ref=sr_1_6
Or use the insert link icon
Tapered Reamer Set
That's one of those tools that I should have bought decades ago. Seems I'm always drilling a hole in metal or plastic and needing to clean up the edges or enlarge it a bit.
I can't believe that I just paid NINE DOLLARS for six rubber grommets! 😡 At least they had the correct size. For that price I almost used double heat shrink instead. The holes in the chassis under the new top plate are nice and smooth. I filed and sanded each new chassis hole I had to make until it was all smooth to the touch.
Now I have some more black painting to do, but with rain and freezing weather, painting is a no go right now. 👎 The PT and one OPT are finished, and the bottom is finished. The chassis, face plate, and one OPT remain. Then decals and multiple clear coats.
Top plate is nice and clean, and everything fits perfectly.
Now I have some more black painting to do, but with rain and freezing weather, painting is a no go right now. 👎 The PT and one OPT are finished, and the bottom is finished. The chassis, face plate, and one OPT remain. Then decals and multiple clear coats.
Top plate is nice and clean, and everything fits perfectly.
You mention an MPS power transformer but he also has some good output transformers in his “HiFi” category.
I bought the OPTs from Primary Windings in the UK last year. Nice man there. I spoke to him by phone.