50 Hz Transformers, or Almost 15 kg of Iron in One Article
It turns out that even the widespread arrival of switching power supplies in our lives—which I’ve told you about in many reviews—hasn’t managed to completely replace conventional transformers. They’re used where a switching power supply isn’t suitable because of its "quirks," especially in linear power supplies, audio equipment, and many applications where interference is undesirable. Today, I’m going to talk about these transformers.
Not long ago, I was looking for a conventional transformer on OLX and came across transformers for (not from, but specifically for) audio equipment several times. They were new, clearly unused, and often intended for Sven equipment.
There’s very little information about them, so I decided to take a brief look at what the “market” has to offer—in other words, describe some 50 Hz transformers you can buy on OLX or Avito.
I ordered a bunch of different transformers. The package was very heavy to carry: the small-looking box weighed almost 11 kg.
The seller wrapped everything carefully, but the postal service still managed to break the plastic fuse holder on one transformer. There was no other damage.
Most of the transformers are shown in this photo, though there will actually be a few more in the article. Calling this a review isn’t quite accurate, though, since it’ll be more like a reference sheet—partly because of the subject matter, and partly to keep it from getting too long.
I’ll cover the transformers in order of increasing weight and, accordingly, power, since these are usually related for 50 Hz transformers.
I’ve also tried to keep all the descriptions consistent to make them easier to compare and follow. In some cases, I’ll also mention typical applications.
I’ll start with the smallest transformer—but no, this one came from Taobao. In fact, there are two of them. They came as a set with VLI level indicators, and with shipping they ended up costing me quite a lot. But since I have them, I might as well include them.
EL41X26
Rated at 8 W, with one tapped secondary winding. The terminal block is very odd: four wires come out, but only three go to the transformer, so the terminal block is probably not original.
1. It weighs 273 g, so the two transformers weigh almost 550 g. With Taobao shipping rates, they cost me more than they would have if I’d bought them locally. I didn’t think the seller would include them with such a low-priced item.
Dimensions:
2. Height
3, 4. Transformer width and width across the mounting points.
5, 6. Transformer thickness and winding bobbin dimensions.
The photos of the weight and dimensions that follow will use the same order.
The construction is very basic; you can see the winding inside. It’s hard to say whether there’s a thermal fuse, but it looks like there is one.
Almost all the output voltage tests were done during one big test session. In any case, the voltage at my home is fairly stable at around 230 V, so if the input voltage is different, the output will change proportionally.
1. A fairly important parameter is no-load current. The lower it is, the better in terms of heating and energy consumption—and for audio equipment, sometimes in terms of performance quality as well.
2. First section of the winding: rated at 4.5 V, but actually almost 6.7 V with no load
3. Second section of the winding: 25 V
4. Total voltage: 32 V, although it was rated at 30 V, if I’ve read the label correctly.
Additional data: winding inductance and resistance. Just to be safe, I’ll also give the resistance readings in parentheses as measured with DC. Also, almost all the photos here correspond to the ones above. For example, if the third photo shows the 25 V winding, the third photo here will show measurements of that same winding.
1. Primary
2. First half of the secondary
3. Second half of the secondary
4. Entire secondary winding
You might ask: why include the inductance data at all? Just as a precaution, in case I come across a defective transformer with a shorted turn. This is often almost impossible to detect by measuring resistance, but the inductance changes dramatically, making the defect easier to spot.
Next up are transformers from OLX.
EL48-C2405
A small, low-power transformer that has already appeared in one of my reviews, of a protection board for speaker systems.
It is rated for two 12 V, 0.5 A windings, i.e. about 12 W of power, but it is also a little larger than the previous one.
The input is just wires; the output has a three-pin connector, with the winding's center tap connected to the middle pin.
Weight, height, width, thickness. Interestingly, this is the only transformer in this article with its winding bobbin mounted vertically rather than horizontally.
The primary winding wires are secured properly, and you can see a thermal fuse inside. By the way, practically every imported transformer I've handled, even Chinese ones, had a thermal fuse inside. Domestic ones are the exact opposite—I can't remember seeing a single one with one. This is most likely due to the higher no-load current and higher operating temperature of imported (mostly Chinese) transformers, but more on that toward the end of the review.
The secondary winding wires aren't secured as well, but they're firmly in place :)
1. Primary winding current with no load
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
The next transformer, like the previous one, was made by CQC. That name doesn't mean anything to me, but this isn't the last transformer from this company today.
TL-48-C2410 - link
This one also has a single output winding with a center tap. The half-windings are also 12 V, but the current is up to 1 A, i.e. up to 24 W of power.
There are no connectors; just wires come out of the transformer. But it does have a fuse, which can sometimes be very convenient.
This one weighs over half a kilo, despite its relatively small size.
The bobbin plastic is opaque, and there are no holes to check the wire diameter. But overall, everything looks neat.
1. Primary winding current with no load
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
And another transformer from CQC, very similar to the previous one, but a little larger.
Model - 33085700280 - link
Everything is like the previous one: no connectors, just wires. A fuse is also fitted to one of the input wires. It also has a single 24 V winding with a center tap, but the current is 1.2 A, giving a power rating of 28.8 W.
Out of curiosity, I compared weight to power. The previous one weighed 548 g and was rated at 24 W; this one weighs 675 g and is rated at 28.8 W. That's a 23% increase in weight, but only a 20% increase in power, so it's not as much more powerful as it is heavier. In my opinion, that's actually better.
You can see the winding wires here; the secondary wires look to be about 0.5 mm in diameter.
But its no-load current is almost one and a half times higher than the previous one's, even though their power ratings are almost the same. That's worse.
1. Primary winding current with no load
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
A transformer with the concise model name AF-11, manufacturer unknown — link
An unusual secondary winding voltage of 2 × 13 V, current up to 2 A, and power of 52 W.
The primary winding connects directly via wires. The secondary wires have a small connector, but in my opinion it's a bit flimsy for 2 A.
This one is considerably heavier, almost a kilogram. Comparing the weight-to-power ratio of this transformer with the 24 W model weighing 548 g, this transformer turns out to be lighter.
The secondary winding wire is slightly thicker than that of the previous 2 A transformer.
1. No-load primary winding current
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
A more complex transformer, model TR-A60. This transformer is used in Sven L5-30r active speakers.
There are no output voltage specifications, but all the wires are terminated with connectors. The input wires are very short, though; this transformer was clearly made for a specific device.
It weighs a little over a kilogram. Based on the weight-to-power ratio of the previous transformers and the number 60 in the model name, I’d guess its output power is around 60 W.
There are three output windings here. One has a center tap, while another has three taps: a center tap and a pair of additional taps.
1. No-load primary winding current
2, 3. The first output winding is a conventional one. Judging by the voltage, I’d guess it was designed for 2 × 10 V under load, with a current probably around 0.5 A.
4, 5. The taps of the second secondary winding are brought out on the green wires. The voltage relative to the common wire is 10–11 V, or 20–22 V across the entire winding.
6. Connecting between different taps gives intermediate voltages, for example 3 V.
7, 8. The ends of the second winding are brought out on the yellow wires. The voltage relative to the common wire is 14.7 V (about 13 V under load), or 29 V (26 V under load) across the entire winding.
9. Connection between the green and yellow wires.
For clarity, here's the winding diagram. If the winding with the blue wires is rated for 0.5 A, its power is about 10 W. The winding with the yellow and green wires is probably rated for 2 A.
Inductance of the windings, corresponding to their voltages in the previous photo. I didn't measure the intermediate options.
And another transformer from CQC, but noticeably more powerful than the previous ones. Model MS-440, used in Sven MS-310, 311, and 321 multimedia systems.
The transformer has a single 22 V winding with a center tap, rated for 2.7 A, with a power of 59.4 W.
Only the output wires have a connector.
The transformers in this article are ordered by increasing weight, and there was a bit of confusion with this one because it weighs only 16 g more than the previous transformer. Actually, the confusion was cleared up once I weighed them: they look almost identical in size, which confirms my estimate that the previous one is rated at 60 W.
The secondary winding wire is quite thick, but for some reason the output wires themselves are thin.
1. No-load primary winding current
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
The transformer model name HT-435R speaks for itself, since it is used in the similarly named SVEN HT435R speaker system.
There are no specifications for the output voltages and currents. The transformer has two windings, each with a center tap; one is clearly the main winding, and the other is auxiliary.
It weighs 1250 grams, which suggests a power rating of around 70–75 W.
The winding wires aren't visible, but the partly empty primary winding bobbin looks interesting (last photo).
1. No-load current of the primary winding
2. Total voltage of the main secondary winding
3, 4. Half-winding voltages.
5, 6. Auxiliary winding voltage, half and total.
It looks like the main winding is rated for around 12–13 V under load (24–26 V total), while the auxiliary winding is rated for 8–9 V.
If we again assume the auxiliary winding is rated for 0.5 A and about 10 W, then the main winding is rated for 2.5–2.6 A.
Additional measurements, corresponding to the photos above.
This transformer looks a little different from all the ones shown earlier. I don't know why, but it reminds me of transformers from some brand-name equipment from the 1980s—maybe because of the dark label, or maybe something else.
The model is BTR5-10(DM-9606), but it's actually much simpler than that: it's used in the SVEN BTR5-10 5.1 system.
The mains wires have no connectors. There are two windings: one rated for 11 V at 0.5 A, and the other for 2 × 14 V at 4 A, giving a calculated power of 117 W.
One of the heaviest transformers on the list, at 1628 grams.
The wires have slipped slightly out of their slots in the bobbin. The main winding is barely visible, so it's hard to determine the wire diameter.
By the way, unlike the previous transformers, this one is specified for an input voltage of 230 V rather than 220 V, so the output voltages are closer to the values on the label.
1. No-load current of the primary winding
2. Auxiliary winding voltage.
3. Voltage of one of the half-windings.
4. Total voltage of the main secondary winding
Additional winding parameters, accordingly.
I've finally reached the transformers I liked the most, and I think you'll agree after seeing them and looking at the measurements.
This one is a toroidal transformer—or rather, two of them, since I plan to build myself an amplifier using a "dual mono" design. I bought some of the modules for it last year and got the rest fairly recently. Now all that's left is to buy an enclosure and a few other odds and ends.
The transformer model is TP-D105-AV106-5, presumably used in one of Sven's receivers.
There are loads of windings here, and they're all genuinely useful.
1. Two mains voltage options
2. Main winding, 2 × 18 V
3. Main winding, 2 × 31 V
4. Auxiliary winding, 9 V
5. Auxiliary winding, 26 V
6. Auxiliary winding, 2 × 1 V.
The second and third windings are used to power the output amplifiers and the analog section.
The third is probably for some kind of relay protection and something else.
The fifth and sixth are clearly for powering the VFD (vacuum fluorescent display).
All the secondary windings are brought out to two connectors. I partly used their appearance to distinguish the main windings from the auxiliary ones.
The transformer weighs almost 2.5 kg, with an estimated power rating of around 180–200 W, which is also supported by some forum comments. Unfortunately, I couldn't identify the exact receiver model.
The wires are terminated very neatly; everything is absolutely new.
Since there are so many windings, I drew a diagram and color-coded the transformer.
I measured the no-load current and other parameters with the primary winding connected both ways, for 220 and 230 V; the input voltage was 228 V.
In my opinion, 13–16 mA is an excellent no-load current for a transformer of this power.
Secondary windings:
1, 2. Indicator heater winding, half and full voltage.
3. Indicator anode winding.
4. Auxiliary 9 V winding.
5, 6. High-voltage power winding, half and full voltage.
7, 8, 9. Low-voltage power winding, two half-windings and full voltage.
Winding inductance, corresponding to the voltage measurements shown above.
Transformer temperatures with no load.
The test order is the same as the order in which the transformers are shown above.
I started with the first five: switched them on, checked them with a thermal camera, waited about an hour, then checked again. In the second thermal image, it looks like the first transformer isn't heating up, but it has simply been "lost" against the others.
EL41X26
EL48-C2405
TL-48-C2410
33085700280
AF-11
They all heat up, and noticeably so, even with no load. Unfortunately, this is a "feature" of transformers like these: manufacturers skimp on the wire and core material. I remember that back when TPП, ТН and other transformer series were widespread, it was considered normal for a transformer to stay cool with no load, and a normal operating temperature was around 60 degrees. Now, an operating temperature closer to 80 or even 100 degrees is considered normal for the transformers shown above. This is partly justified, since they may use wire with more heat-resistant insulation, but personally, I'm not very used to operating temperatures like these.
The second batch of five transformers, again in the same order as shown above.
TR-A60
MS-440
HT-435R
BTR5-10(DM-9606)
TP-D105-AV106-5
The results are almost the same as before, but the last transformer showed how a truly high-quality transformer should perform. It's a shame that transformers like this are quite expensive, but I think they're worth it.
Since I've started writing about transformers, I decided to add a couple more models that I showed earlier in two reviews of electronic load modifications: models 109-01AF31-01 and 109-01L530-01 - link. As you can see, the battery labels are very similar, and the transformers themselves have similar specifications.
The first transformer has an output of 2 × 12 V at up to 3.5 A, while the second is 2 × 15 V at 3 A. The first is rated at 84 W, the second at 90 W, but I think their actual power ratings are the same.
The batteries' weights and dimensions are also almost identical, which is why I assumed their power ratings were the same.
On the left is the 12 V, 3.5 A transformer; on the right, the 15 V, 3 A one. The measurements shown are the no-load current, half-winding voltage, and full-winding voltage, respectively.
With no load, both transformers reach roughly the same temperature.
To sum up briefly: by and large, all the transformers except the toroidal one are about the same, and their temperatures are similar too. One advantage is that almost all of them have center-tapped windings, so it's easy to get a dual-polarity supply for audio amplifiers.
They can also be used in small bench power supplies, with two windings switched as I did in my review of a microcontroller-controlled linear power supply.
Low-power transformers are also suitable for powering a digitally controlled electronic load, where this supply is used to ensure the op-amps work correctly.
I'll say a few words about the toroidal one separately. I really liked the transformer. Its specs and output voltages are just right for powering power amplifiers, plus it can power the VLI level indicators. And the best part is that I have two of them, so I can build a stereo amplifier with a true dual-mono setup.
That’s all from me. I hope this information is useful and may help you choose a replacement transformer for an active speaker or amplifier.
Not long ago, I was looking for a conventional transformer on OLX and came across transformers for (not from, but specifically for) audio equipment several times. They were new, clearly unused, and often intended for Sven equipment.
There’s very little information about them, so I decided to take a brief look at what the “market” has to offer—in other words, describe some 50 Hz transformers you can buy on OLX or Avito.
I ordered a bunch of different transformers. The package was very heavy to carry: the small-looking box weighed almost 11 kg.
The seller wrapped everything carefully, but the postal service still managed to break the plastic fuse holder on one transformer. There was no other damage.
Most of the transformers are shown in this photo, though there will actually be a few more in the article. Calling this a review isn’t quite accurate, though, since it’ll be more like a reference sheet—partly because of the subject matter, and partly to keep it from getting too long.
I’ll cover the transformers in order of increasing weight and, accordingly, power, since these are usually related for 50 Hz transformers.
I’ve also tried to keep all the descriptions consistent to make them easier to compare and follow. In some cases, I’ll also mention typical applications.
I’ll start with the smallest transformer—but no, this one came from Taobao. In fact, there are two of them. They came as a set with VLI level indicators, and with shipping they ended up costing me quite a lot. But since I have them, I might as well include them.
EL41X26
Rated at 8 W, with one tapped secondary winding. The terminal block is very odd: four wires come out, but only three go to the transformer, so the terminal block is probably not original.
1. It weighs 273 g, so the two transformers weigh almost 550 g. With Taobao shipping rates, they cost me more than they would have if I’d bought them locally. I didn’t think the seller would include them with such a low-priced item.
Dimensions:
2. Height
3, 4. Transformer width and width across the mounting points.
5, 6. Transformer thickness and winding bobbin dimensions.
The photos of the weight and dimensions that follow will use the same order.
The construction is very basic; you can see the winding inside. It’s hard to say whether there’s a thermal fuse, but it looks like there is one.
Almost all the output voltage tests were done during one big test session. In any case, the voltage at my home is fairly stable at around 230 V, so if the input voltage is different, the output will change proportionally.
1. A fairly important parameter is no-load current. The lower it is, the better in terms of heating and energy consumption—and for audio equipment, sometimes in terms of performance quality as well.
2. First section of the winding: rated at 4.5 V, but actually almost 6.7 V with no load
3. Second section of the winding: 25 V
4. Total voltage: 32 V, although it was rated at 30 V, if I’ve read the label correctly.
Additional data: winding inductance and resistance. Just to be safe, I’ll also give the resistance readings in parentheses as measured with DC. Also, almost all the photos here correspond to the ones above. For example, if the third photo shows the 25 V winding, the third photo here will show measurements of that same winding.
1. Primary
2. First half of the secondary
3. Second half of the secondary
4. Entire secondary winding
You might ask: why include the inductance data at all? Just as a precaution, in case I come across a defective transformer with a shorted turn. This is often almost impossible to detect by measuring resistance, but the inductance changes dramatically, making the defect easier to spot.
Next up are transformers from OLX.
EL48-C2405
A small, low-power transformer that has already appeared in one of my reviews, of a protection board for speaker systems.
It is rated for two 12 V, 0.5 A windings, i.e. about 12 W of power, but it is also a little larger than the previous one.
The input is just wires; the output has a three-pin connector, with the winding's center tap connected to the middle pin.
Weight, height, width, thickness. Interestingly, this is the only transformer in this article with its winding bobbin mounted vertically rather than horizontally.
The primary winding wires are secured properly, and you can see a thermal fuse inside. By the way, practically every imported transformer I've handled, even Chinese ones, had a thermal fuse inside. Domestic ones are the exact opposite—I can't remember seeing a single one with one. This is most likely due to the higher no-load current and higher operating temperature of imported (mostly Chinese) transformers, but more on that toward the end of the review.
The secondary winding wires aren't secured as well, but they're firmly in place :)
1. Primary winding current with no load
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
The next transformer, like the previous one, was made by CQC. That name doesn't mean anything to me, but this isn't the last transformer from this company today.
TL-48-C2410 - link
This one also has a single output winding with a center tap. The half-windings are also 12 V, but the current is up to 1 A, i.e. up to 24 W of power.
There are no connectors; just wires come out of the transformer. But it does have a fuse, which can sometimes be very convenient.
This one weighs over half a kilo, despite its relatively small size.
The bobbin plastic is opaque, and there are no holes to check the wire diameter. But overall, everything looks neat.
1. Primary winding current with no load
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
And another transformer from CQC, very similar to the previous one, but a little larger.
Model - 33085700280 - link
Everything is like the previous one: no connectors, just wires. A fuse is also fitted to one of the input wires. It also has a single 24 V winding with a center tap, but the current is 1.2 A, giving a power rating of 28.8 W.
Out of curiosity, I compared weight to power. The previous one weighed 548 g and was rated at 24 W; this one weighs 675 g and is rated at 28.8 W. That's a 23% increase in weight, but only a 20% increase in power, so it's not as much more powerful as it is heavier. In my opinion, that's actually better.
You can see the winding wires here; the secondary wires look to be about 0.5 mm in diameter.
But its no-load current is almost one and a half times higher than the previous one's, even though their power ratings are almost the same. That's worse.
1. Primary winding current with no load
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
A transformer with the concise model name AF-11, manufacturer unknown — link
An unusual secondary winding voltage of 2 × 13 V, current up to 2 A, and power of 52 W.
The primary winding connects directly via wires. The secondary wires have a small connector, but in my opinion it's a bit flimsy for 2 A.
This one is considerably heavier, almost a kilogram. Comparing the weight-to-power ratio of this transformer with the 24 W model weighing 548 g, this transformer turns out to be lighter.
The secondary winding wire is slightly thicker than that of the previous 2 A transformer.
1. No-load primary winding current
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
A more complex transformer, model TR-A60. This transformer is used in Sven L5-30r active speakers.
There are no output voltage specifications, but all the wires are terminated with connectors. The input wires are very short, though; this transformer was clearly made for a specific device.
It weighs a little over a kilogram. Based on the weight-to-power ratio of the previous transformers and the number 60 in the model name, I’d guess its output power is around 60 W.
There are three output windings here. One has a center tap, while another has three taps: a center tap and a pair of additional taps.
1. No-load primary winding current
2, 3. The first output winding is a conventional one. Judging by the voltage, I’d guess it was designed for 2 × 10 V under load, with a current probably around 0.5 A.
4, 5. The taps of the second secondary winding are brought out on the green wires. The voltage relative to the common wire is 10–11 V, or 20–22 V across the entire winding.
6. Connecting between different taps gives intermediate voltages, for example 3 V.
7, 8. The ends of the second winding are brought out on the yellow wires. The voltage relative to the common wire is 14.7 V (about 13 V under load), or 29 V (26 V under load) across the entire winding.
9. Connection between the green and yellow wires.
For clarity, here's the winding diagram. If the winding with the blue wires is rated for 0.5 A, its power is about 10 W. The winding with the yellow and green wires is probably rated for 2 A.
Inductance of the windings, corresponding to their voltages in the previous photo. I didn't measure the intermediate options.
And another transformer from CQC, but noticeably more powerful than the previous ones. Model MS-440, used in Sven MS-310, 311, and 321 multimedia systems.
The transformer has a single 22 V winding with a center tap, rated for 2.7 A, with a power of 59.4 W.
Only the output wires have a connector.
The transformers in this article are ordered by increasing weight, and there was a bit of confusion with this one because it weighs only 16 g more than the previous transformer. Actually, the confusion was cleared up once I weighed them: they look almost identical in size, which confirms my estimate that the previous one is rated at 60 W.
The secondary winding wire is quite thick, but for some reason the output wires themselves are thin.
1. No-load primary winding current
2. Total secondary winding voltage
3, 4. Half-winding voltages.
1. Primary winding
2. Entire secondary winding
3, 4. Half-windings
The transformer model name HT-435R speaks for itself, since it is used in the similarly named SVEN HT435R speaker system.
There are no specifications for the output voltages and currents. The transformer has two windings, each with a center tap; one is clearly the main winding, and the other is auxiliary.
It weighs 1250 grams, which suggests a power rating of around 70–75 W.
The winding wires aren't visible, but the partly empty primary winding bobbin looks interesting (last photo).
1. No-load current of the primary winding
2. Total voltage of the main secondary winding
3, 4. Half-winding voltages.
5, 6. Auxiliary winding voltage, half and total.
It looks like the main winding is rated for around 12–13 V under load (24–26 V total), while the auxiliary winding is rated for 8–9 V.
If we again assume the auxiliary winding is rated for 0.5 A and about 10 W, then the main winding is rated for 2.5–2.6 A.
Additional measurements, corresponding to the photos above.
This transformer looks a little different from all the ones shown earlier. I don't know why, but it reminds me of transformers from some brand-name equipment from the 1980s—maybe because of the dark label, or maybe something else.
The model is BTR5-10(DM-9606), but it's actually much simpler than that: it's used in the SVEN BTR5-10 5.1 system.
The mains wires have no connectors. There are two windings: one rated for 11 V at 0.5 A, and the other for 2 × 14 V at 4 A, giving a calculated power of 117 W.
One of the heaviest transformers on the list, at 1628 grams.
The wires have slipped slightly out of their slots in the bobbin. The main winding is barely visible, so it's hard to determine the wire diameter.
By the way, unlike the previous transformers, this one is specified for an input voltage of 230 V rather than 220 V, so the output voltages are closer to the values on the label.
1. No-load current of the primary winding
2. Auxiliary winding voltage.
3. Voltage of one of the half-windings.
4. Total voltage of the main secondary winding
Additional winding parameters, accordingly.
I've finally reached the transformers I liked the most, and I think you'll agree after seeing them and looking at the measurements.
This one is a toroidal transformer—or rather, two of them, since I plan to build myself an amplifier using a "dual mono" design. I bought some of the modules for it last year and got the rest fairly recently. Now all that's left is to buy an enclosure and a few other odds and ends.
The transformer model is TP-D105-AV106-5, presumably used in one of Sven's receivers.
There are loads of windings here, and they're all genuinely useful.
1. Two mains voltage options
2. Main winding, 2 × 18 V
3. Main winding, 2 × 31 V
4. Auxiliary winding, 9 V
5. Auxiliary winding, 26 V
6. Auxiliary winding, 2 × 1 V.
The second and third windings are used to power the output amplifiers and the analog section.
The third is probably for some kind of relay protection and something else.
The fifth and sixth are clearly for powering the VFD (vacuum fluorescent display).
All the secondary windings are brought out to two connectors. I partly used their appearance to distinguish the main windings from the auxiliary ones.
The transformer weighs almost 2.5 kg, with an estimated power rating of around 180–200 W, which is also supported by some forum comments. Unfortunately, I couldn't identify the exact receiver model.
The wires are terminated very neatly; everything is absolutely new.
Since there are so many windings, I drew a diagram and color-coded the transformer.
I measured the no-load current and other parameters with the primary winding connected both ways, for 220 and 230 V; the input voltage was 228 V.
In my opinion, 13–16 mA is an excellent no-load current for a transformer of this power.
Secondary windings:
1, 2. Indicator heater winding, half and full voltage.
3. Indicator anode winding.
4. Auxiliary 9 V winding.
5, 6. High-voltage power winding, half and full voltage.
7, 8, 9. Low-voltage power winding, two half-windings and full voltage.
Winding inductance, corresponding to the voltage measurements shown above.
Transformer temperatures with no load.
The test order is the same as the order in which the transformers are shown above.
I started with the first five: switched them on, checked them with a thermal camera, waited about an hour, then checked again. In the second thermal image, it looks like the first transformer isn't heating up, but it has simply been "lost" against the others.
EL41X26
EL48-C2405
TL-48-C2410
33085700280
AF-11
They all heat up, and noticeably so, even with no load. Unfortunately, this is a "feature" of transformers like these: manufacturers skimp on the wire and core material. I remember that back when TPП, ТН and other transformer series were widespread, it was considered normal for a transformer to stay cool with no load, and a normal operating temperature was around 60 degrees. Now, an operating temperature closer to 80 or even 100 degrees is considered normal for the transformers shown above. This is partly justified, since they may use wire with more heat-resistant insulation, but personally, I'm not very used to operating temperatures like these.
The second batch of five transformers, again in the same order as shown above.
TR-A60
MS-440
HT-435R
BTR5-10(DM-9606)
TP-D105-AV106-5
The results are almost the same as before, but the last transformer showed how a truly high-quality transformer should perform. It's a shame that transformers like this are quite expensive, but I think they're worth it.
Since I've started writing about transformers, I decided to add a couple more models that I showed earlier in two reviews of electronic load modifications: models 109-01AF31-01 and 109-01L530-01 - link. As you can see, the battery labels are very similar, and the transformers themselves have similar specifications.
The first transformer has an output of 2 × 12 V at up to 3.5 A, while the second is 2 × 15 V at 3 A. The first is rated at 84 W, the second at 90 W, but I think their actual power ratings are the same.
The batteries' weights and dimensions are also almost identical, which is why I assumed their power ratings were the same.
On the left is the 12 V, 3.5 A transformer; on the right, the 15 V, 3 A one. The measurements shown are the no-load current, half-winding voltage, and full-winding voltage, respectively.
With no load, both transformers reach roughly the same temperature.
To sum up briefly: by and large, all the transformers except the toroidal one are about the same, and their temperatures are similar too. One advantage is that almost all of them have center-tapped windings, so it's easy to get a dual-polarity supply for audio amplifiers.
They can also be used in small bench power supplies, with two windings switched as I did in my review of a microcontroller-controlled linear power supply.
Low-power transformers are also suitable for powering a digitally controlled electronic load, where this supply is used to ensure the op-amps work correctly.
I'll say a few words about the toroidal one separately. I really liked the transformer. Its specs and output voltages are just right for powering power amplifiers, plus it can power the VLI level indicators. And the best part is that I have two of them, so I can build a stereo amplifier with a true dual-mono setup.
That’s all from me. I hope this information is useful and may help you choose a replacement transformer for an active speaker or amplifier.
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