I picked up the soldering iron for the first time last night. Fortunately, I picked it up by the correct end. I made that mistake once as a kid, and I won't ever do that again.
- Lots of delays, primarily that fact that this is a learning experience more than a kit build, so I have been doing extensive research and learning for several weeks.
- I spent a lot of time translating from Chinese to English, including the directions and also obtaining the exact specifications for the Chinese tubes, which were not easy to get.
- I already have a Dynaco ST-70 series ii that I recently took out of mothballs, so there is no extreme urgency for me to build another tube amp.
- I spent some time researching a cheap DAC to use as a volume control and DAC with the Dynaco. It should be arriving from China today. No idea how that will sound.
- Had to invest time to find a reasonable way to switch between 2 amplifiers - home theater receiver and tube amp. Ended up with the simplest solution which is banana plugs that I can reach without moving furniture or speakers. I am making some new speaker cables anyway to replace my 30+ year old Monster Cable. One day I will build or buy a switch box to do the amplifier switching. Banana plugs arrived yesterday. Wire is en route from China.
- I couldn't stand the all silver amplifier chassis, so I spent several days carefully painting each piece and each screw satin black. Although the front panel is still silver for now, I have had custom white decals made for the power and volume controls in case I decide to paint the front black. Decals arrived yesterday.
- As long as I was fiddling with the chassis, I added some cable clips inside that screw in place to keep the input signal wires from flopping around. One kit builder on YouTube used glue, and I didn't like that approach.
- Searched for and purchased plugs to fill the holes in the chassis where the magic eye tubes will not be installed. They fit perfectly. They are $1 plastic plugs. I can "upgrade" to $6 each metal plugs later, LOL. I have no idea why they cost so much
- Ordered some upgraded electronic components from Mouser. Package arrived today.
- The Chinese seller (worst I have ever dealt with) argued for days about sending me the missing gold nuts for the speaker binding posts. I gave up and ordered another pair of binding posts, en route from China. After filing a complaint against the seller, they finally agreed to ship the parts from China the day before yesterday.
- I decided to order gold plated RCA input jacks that I hope will prevent corrosion. En route from China. Unfortunately, the ones on my Dynaco do have some corrosion after 30 years despite being gold plated.
- I went through my enormous plastic tub of scrap wire, mostly tangled in knots, and finally sorted out enough appropriate wire in multiple colors to upgrade everything that came in the kit.
- I ordered a new multimeter to replace my 30 year old Radio Shack model. It was past time. So I had to wait for that. Then I took an evening to precision match everything in pairs, whether "necessary" or not. It costs nothing, so why not.
- I spent a significant amount of time to see if this amp could be built point-to-point, only to conclude that it cannot due to extremely tight space inside the very small chassis. I will use the circuit board but will use point-to-point jumpers where possible. This technique is recommended by the manufacturer in several locations because circuit board traces are not always ideal.
I also started putting the resistors on the amplifier board last night, along with a few jumpers and a better ground bus to figure out how that would work. Silver plated solid copper jewelry wire from the local craft store turned out to be the simplest and cheapest way to make jumpers where needed. Most just go over the traces already on the board. I have used this technique on other boards in the past, including speakers that had crossovers built on circuit boards - I can't stand that.
Hey, take your time and don't listen to silly old men like me. 🙂
Sounds like you're having fun and learning, and that's what counts.
jeff
Sounds like you're having fun and learning, and that's what counts.
jeff
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I tested the power transformer and power supply board without blowing anything up or electrocuting myself. 😀
Now I am concerned about the voltages and wondering if I need the "optional" 91V zener diode that was included in the kit, I assume to replace one of the three 100V zener diodes. I'm still not sure why that zener diode is included, and the instructions are silent. In the build video, xraytonyb said those three zener diodes somehow control the 330V output?
I assume the rest of the voltages are all high due to my wall voltage being 121VAC instead of 115VAC, plus it appears to me that the "115V" transformer included is more like 110V as was shown in the old directions from several years ago. Maybe they just changed the label on the transformer and not the transformer itself to try to fool people.
How big a problem is this?
These are the voltages I am supposed to have at no load during testing per the directions:
Transformer specifications (no load) vs. actual (no load)
115VAC in -> actual 121VAC
275VAV out -> actual 300VAC
6.3VAC out -> actual 9.6VAC
3.25VAC out -> actual 3.5VAC
Power supply specifications (no load) vs. actual (no load)
380V out -> actual 414V
295V - 300V not to exceed 300V -> actual 311V ... the directions are very specific not to exceed 300V here
On the advice of someone here at diyAudio, I did purchase a couple of small resistors to put inline with the filaments if needed.
Is there any real solution other than purchasing a power supply that will feed the amplifier 110 volts instead of 121? This seems to be an issue with all of these Chinese amplifiers. Interestingly, my 30 year old Dynaco ST-70 series ii also says 115V on the back of the amplifier.
Now I am concerned about the voltages and wondering if I need the "optional" 91V zener diode that was included in the kit, I assume to replace one of the three 100V zener diodes. I'm still not sure why that zener diode is included, and the instructions are silent. In the build video, xraytonyb said those three zener diodes somehow control the 330V output?
I assume the rest of the voltages are all high due to my wall voltage being 121VAC instead of 115VAC, plus it appears to me that the "115V" transformer included is more like 110V as was shown in the old directions from several years ago. Maybe they just changed the label on the transformer and not the transformer itself to try to fool people.
How big a problem is this?
These are the voltages I am supposed to have at no load during testing per the directions:
Transformer specifications (no load) vs. actual (no load)
115VAC in -> actual 121VAC
275VAV out -> actual 300VAC
6.3VAC out -> actual 9.6VAC
3.25VAC out -> actual 3.5VAC
Power supply specifications (no load) vs. actual (no load)
380V out -> actual 414V
295V - 300V not to exceed 300V -> actual 311V ... the directions are very specific not to exceed 300V here
On the advice of someone here at diyAudio, I did purchase a couple of small resistors to put inline with the filaments if needed.
Is there any real solution other than purchasing a power supply that will feed the amplifier 110 volts instead of 121? This seems to be an issue with all of these Chinese amplifiers. Interestingly, my 30 year old Dynaco ST-70 series ii also says 115V on the back of the amplifier.
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Is it as simple as increasing R1 by about 20-30 ohms?
Calculator: https://www.ampbooks.com/mobile/amplifier-calculators/RC-ripple-filter/calculator/
Calculator: https://www.ampbooks.com/mobile/amplifier-calculators/RC-ripple-filter/calculator/
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It is not going to hurt to run it for a short time with the transformer properly loaded, filments drawing current and the tubes conducting. The difference is not too great. Aim to be abe to get the key measurements quickly, then switch on, probe a bit (one hand, one multimeter lead to the ground). Then one more iteration to grab the heater voltages.
It could be better than you think.
I use a CL90 ICL (inrush current limiter) on the primary side of the transformer, and a CL140 on the secondary side, as recommended by Tubelab on the SPP instructions. This will shave off a few volts, and prevents a start up jolt. But you can fix that later when you have all the real data.
It could be better than you think.
I use a CL90 ICL (inrush current limiter) on the primary side of the transformer, and a CL140 on the secondary side, as recommended by Tubelab on the SPP instructions. This will shave off a few volts, and prevents a start up jolt. But you can fix that later when you have all the real data.
If it's already out of spec for no-load testing per the instructions, how is it going to improve with load on it? I must be missing something. Plus I have eliminated two tubes from the build - the two magic eye tubes - so that's less power draw there too.
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Eliminating the two tubes will not help, but is solvable. My point is that if you have an issue with voltages you will need to know the current consumed and voltages so that you can plan to mitigate it. In my opininion the differences arenot so great that you risk damaging anything gathering the real (loaded) data.
There are various options to shave off a few volts, or if it is a lot of volts, use something like a bucking transformer.
There are various options to shave off a few volts, or if it is a lot of volts, use something like a bucking transformer.
According to rough calculations and another source I can't remember, total current at amplifier max power is about .8 to 1 amp. Transformer is rated for 1.2 amps, so that makes sense I guess.
Using the calculator I found, changing R1 from 100 ohms to about 120 ohms increases ripple attenuation and also drops the voltage at the same time. Isn't that a win-win? It seems like, with a 10 watt rating, it's just sitting there burning off a lot of power anyway, so why not just burn off a little more right there? Or am I missing something obvious to others not a novice like me? 😕 I am learning though, the point of this exercise! 😀
I happen to have a 20 watt 20 ohm resistor sitting here from decades ago that I could test wire in series with R1 for testing.
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Then there is the 6P14 problem with the Chinese output tubes requiring regulation. Per the manufacturer, the 6P14 absolutely must not have over 300V on the screen or it will fry itself, so the regulation apparently needs to be changed too.
I'll likely build and sell the amplifier if I have to go that far.
Using the calculator I found, changing R1 from 100 ohms to about 120 ohms increases ripple attenuation and also drops the voltage at the same time. Isn't that a win-win? It seems like, with a 10 watt rating, it's just sitting there burning off a lot of power anyway, so why not just burn off a little more right there? Or am I missing something obvious to others not a novice like me? 😕 I am learning though, the point of this exercise! 😀
I happen to have a 20 watt 20 ohm resistor sitting here from decades ago that I could test wire in series with R1 for testing.
Before:
After:
Then there is the 6P14 problem with the Chinese output tubes requiring regulation. Per the manufacturer, the 6P14 absolutely must not have over 300V on the screen or it will fry itself, so the regulation apparently needs to be changed too.
I'll likely build and sell the amplifier if I have to go that far.
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I overlooked the fact that most of that transformer power goes to the filaments. Oops. Current at that resistor more likely is something around a couple hundred mA not 1000mA I guess. Duh. It's only a 12 watt/channel amp. I must have been really tired last night. 🥱
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Is there an (easy) way to put a load on the high voltage power supply while there is a delay building the rest of the amp? Like I said, the power supply is already well out of spec with the manufacturer's no-load values. The directions say not to proceed if the voltages are not correct, and they aren't.
Add a high power load resistor to the power supply, equal to the nominal HV divided by the current that will be drawn
during normal operation. Use several equal resistors in series, if the resistors have inadequate voltage rating limitations.
during normal operation. Use several equal resistors in series, if the resistors have inadequate voltage rating limitations.
About 2-3 times the actual dissipation, which = HV^2 / (resistance)
Be sure to mount the resistor(s) in free air, well away from anything flammable.
Be sure to mount the resistor(s) in free air, well away from anything flammable.
Or several small ones connected together appropriately. Most people have a junk box to scrounge from.
I do, but only some carbon film 1/4 and 1/2 watt, a few high-power ceramic ones from speaker crossovers that are a few ohms each up to 50 ohms, and two 100 ohm ceramic 10 watt.
These are the voltages I am supposed to have at no load during testing per the directions:
Transformer specifications (no load) vs. actual (no load)
115VAC in -> actual 121VAC from my wall outlet
275VAC out -> actual 300VAC
6.3VAC out -> actual 9.6VAC
3.25VAC out -> actual 3.5VAC
Power supply board oputput specifications (no load) vs. actual (no load)
380V out -> actual 414V
295V - 300V out not to exceed 300V -> actual 311V ... the directions are very specific not to exceed 300V here and it's supposed to be regulated to 295V to 300V. They included a 91V zener diode labeled "optional" I suspect for this purpose to replace one of the 100V? Apparently, the Chinese 6P14 blows up very quickly over 300V on the screen, sometimes immediately.
Transformer specifications (no load) vs. actual (no load)
115VAC in -> actual 121VAC from my wall outlet
275VAC out -> actual 300VAC
6.3VAC out -> actual 9.6VAC
3.25VAC out -> actual 3.5VAC
Power supply board oputput specifications (no load) vs. actual (no load)
380V out -> actual 414V
295V - 300V out not to exceed 300V -> actual 311V ... the directions are very specific not to exceed 300V here and it's supposed to be regulated to 295V to 300V. They included a 91V zener diode labeled "optional" I suspect for this purpose to replace one of the 100V? Apparently, the Chinese 6P14 blows up very quickly over 300V on the screen, sometimes immediately.
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Well being that I'm lazy, I would just increase the value of R1. Any idea what the current thru R1 would be under load, maybe 160ma?
jeff
jeff
I suspect about that. According to knowledgeable people, the current at idle through the 4 output tubes is roughly 30mA per tube = 120mA, plus 12 watts/channel max when driven hard, plus whatever the two 6N1 tubes need.
I am hoping that in this particular situation, changing R1 and one of the three zener diodes with the included "optional" 91V diode is the simple answer.