I'm starting this thread to add measurements I've performed on some Edcor output transformers, so that desingngers can refer to this thread when considering a given Edcor transformer for a design. Other folks are more than welcome to chip in with their measurements.
To roughly characterize a transformer, I throw it on the bench and apply 50V, 300 Hz to the primary. The 50V input voltage ensures a good flux swing so that I can get an inductance reading applicable to real working conditions. I use 300 JHz to ensure that the input excitation is in-band, so that I can get a reasonably accurate number for the turns ratio. Anway, I feed the primary with a 50V, 300 Hz signal, read the output RMS voltage with a DVM, and read the no-load excitation current using a Yokogawa WT210 wattmeter. The transformer primary inductance can be calculated from the excitation current, and the excitation voltage and frequency. All this gets me the turns ratio, so that I can calculate the transformer primary reflected impedance. The turns ratio is also an important number in it's own right, and I generally use that number rather than the impedance to calculate operating end point. for a given design.
Anyway, the first set of numbers is from an Edcor GXSE15-8-5k. With 50V, 300 Hz excitation, the output voltage is 1.998V, so that the turns ratio is 25.02 :1. For the rated 8 ohm output, the reflected impedance at the primary is 5010 ohms, pretty much right on the money. No-load excitation was measured as 1.59 mA. The formula Lp = Vin/(6.28*fin*Iin) was used to calculate primary inductance. Vin = input voltage =50V. Fin = input frequency = 300 Hz. Iin = excitation current + 1.59 mA. This yields a primary inductance of ~17.7H, fairly respectable for a small sized transformer, and no doubt a compromise between low frequency extension and primary current handling capability, limited by saturation rather than overheating.
Next up, I'll post some numbers on one of the bitty XSE transformers.
To roughly characterize a transformer, I throw it on the bench and apply 50V, 300 Hz to the primary. The 50V input voltage ensures a good flux swing so that I can get an inductance reading applicable to real working conditions. I use 300 JHz to ensure that the input excitation is in-band, so that I can get a reasonably accurate number for the turns ratio. Anway, I feed the primary with a 50V, 300 Hz signal, read the output RMS voltage with a DVM, and read the no-load excitation current using a Yokogawa WT210 wattmeter. The transformer primary inductance can be calculated from the excitation current, and the excitation voltage and frequency. All this gets me the turns ratio, so that I can calculate the transformer primary reflected impedance. The turns ratio is also an important number in it's own right, and I generally use that number rather than the impedance to calculate operating end point. for a given design.
Anyway, the first set of numbers is from an Edcor GXSE15-8-5k. With 50V, 300 Hz excitation, the output voltage is 1.998V, so that the turns ratio is 25.02 :1. For the rated 8 ohm output, the reflected impedance at the primary is 5010 ohms, pretty much right on the money. No-load excitation was measured as 1.59 mA. The formula Lp = Vin/(6.28*fin*Iin) was used to calculate primary inductance. Vin = input voltage =50V. Fin = input frequency = 300 Hz. Iin = excitation current + 1.59 mA. This yields a primary inductance of ~17.7H, fairly respectable for a small sized transformer, and no doubt a compromise between low frequency extension and primary current handling capability, limited by saturation rather than overheating.
Next up, I'll post some numbers on one of the bitty XSE transformers.
Thank you Wrenchone!
My experience with Edcor calls for measurement of stray inductance for big transformers. Can you do that?
Also, some small 15K:600 Ohm line level transformers have too low for 15K inductance... Is it a joke, or I misunderstand something?
My experience with Edcor calls for measurement of stray inductance for big transformers. Can you do that?
Also, some small 15K:600 Ohm line level transformers have too low for 15K inductance... Is it a joke, or I misunderstand something?
Shorting the secondary and measuring the current would give you the total leakage inductance referred to the primary. Obviously, you'd have to limit the drive signal amplitude when you do this.
I measured some Edcor transformers on an HP 4194A Impedance/Gain-Phase Analyzer and used its equivalent circuit function to calculate the L, R and C from the impedance sweep. I measured the primary impedance when loaded by 8 ohm on the secondary. DC resistances were measured with a 6-digit DMM using a 4-wire setup (Kevin connection). Here's what I came up with:
XSE15-8-5K: Lp = 2.43 H; Cp = 233 pF; Lleakage = 4.66 mH. Primary impedance magnitude when loaded by 8 ohm on secondary: 5.10 kOhm @ 2 kHz. R(DC) of primary: 87.44 Ohm. R(DC) of secondary: 0.264 Ohm.
CXSE25-8-5K: Lp = 13.86 H; Cp = 1.541 nF; Lleakage = 10.32 mH. Primary impedance magnitude when loaded by 8 ohm on the secondary: 4.42 kOhm @ 2 kHz. R(DC) of primary: 80.83 Ohm. R(DC) of secondary: 0.361 ohm.
I'm surprised the primary impedance is 4.4 kOhm not 5.0 kOhm as specified. I ordered two transformers. They both measure 4.4 kOhm. It doesn't make a big difference in real life, I'm just surprised...
~Tom
I measured some Edcor transformers on an HP 4194A Impedance/Gain-Phase Analyzer and used its equivalent circuit function to calculate the L, R and C from the impedance sweep. I measured the primary impedance when loaded by 8 ohm on the secondary. DC resistances were measured with a 6-digit DMM using a 4-wire setup (Kevin connection). Here's what I came up with:
XSE15-8-5K: Lp = 2.43 H; Cp = 233 pF; Lleakage = 4.66 mH. Primary impedance magnitude when loaded by 8 ohm on secondary: 5.10 kOhm @ 2 kHz. R(DC) of primary: 87.44 Ohm. R(DC) of secondary: 0.264 Ohm.
CXSE25-8-5K: Lp = 13.86 H; Cp = 1.541 nF; Lleakage = 10.32 mH. Primary impedance magnitude when loaded by 8 ohm on the secondary: 4.42 kOhm @ 2 kHz. R(DC) of primary: 80.83 Ohm. R(DC) of secondary: 0.361 ohm.
I'm surprised the primary impedance is 4.4 kOhm not 5.0 kOhm as specified. I ordered two transformers. They both measure 4.4 kOhm. It doesn't make a big difference in real life, I'm just surprised...
~Tom
I find that inductance numbers measured at low level excitation aren't too repeatable, and also vary with frequency. That's why I use a high level sinewave source to apply a healthy voltage with real current capability to the transformer primary. I started out using our usual inductance meter, and the numbers I got were way low. We also have an HP4194A at work. I find it very useful for other measurements and for SMPS transformers, but I dont trust the low level measurements with 60Hz transformers. Driving the transformer with a good healthy signal and using the 4194 to measure parasitics may be useful.
I've been wanting to build a saturation tester to apply a fixed voltage to a transformer primary with a mosfet switch in order to look at the current ramp, with a protective current-actuated shutdown to protect the transformer, along with a healthy voltage clamp across the primary. This would be useful to determine the real current rating for a given transformer primary, as well as a way to sort out NOS/unknown transformers. This could be used to evaluate SE transformers as well as determining the volt-seconds rating for a push-pull unit.
I've been wanting to build a saturation tester to apply a fixed voltage to a transformer primary with a mosfet switch in order to look at the current ramp, with a protective current-actuated shutdown to protect the transformer, along with a healthy voltage clamp across the primary. This would be useful to determine the real current rating for a given transformer primary, as well as a way to sort out NOS/unknown transformers. This could be used to evaluate SE transformers as well as determining the volt-seconds rating for a push-pull unit.
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To accurately reflect performance in the circuit, the transformer should have a DC bias applied to it as well.
I haven't had any issues with repeatability of my measurements on the 4194A, though. LCR meters, that's another story...
~Tom
I haven't had any issues with repeatability of my measurements on the 4194A, though. LCR meters, that's another story...
~Tom
Talked to the guys at Edcor the other day and they specified the 25W 5k having 50H primary inductance at 1kHz. Quite a bit from the measured above. Also max current 125mA.
Its seems to me that most of the Edcor designs don't always have as much inductance as I'd like. I had some custom SE transformers wound that have a 15% cathode feedback winding. It was a small 10W model 3.5K : 16/8/4. I used it for a small Class A2 amp for my desk. Anyway, the primary inductance measured in at 13H. Thank goodness for the CFB, otherwise I would have had zero bass.
I realize this thread is about Edcor's output transformers, but how good are their power transformers? The particular one I was looking at was quite a bit cheaper than the same spec'd Hammond. Thanks.
PWR RYD, I have purchased about 4 or 5 power transformers from Edor. Of there 2 were custom to my design. All have been quality built products that have performed right on to where they were sped'd. I believe they are a real quality built product. Mickeystan
According to my experience, their power transformers are perfect. At least, my 360 VA Pyramid series.
I purchased an Edcor power x-former for a recent 2A3 build and it seems to be of high quality for the price. As you indicated, less than Hammond, which I have used too.
It has slightly high output with 120VAC input (filament taps), but other than that it seems to be doing great so far. The main HT tap is rated for 200mA and I am only pulling about 125mA, (all other taps are using their rated loads) which may explain why the other voltages are high. I would not think 75mA would make that much difference, but possibly.
If the input to the transformer is reduced to 115VAC from 120VAC, all voltages are right on the money.
Actually the slightly hight filament voltage is a good thing; you can always put some resistance in series and that is a good "shock absorber" for the tube filament.
When filament voltage is too low you have a problem...
When filament voltage is too low you have a problem...
I've only good experiences with Edcors. I've even had great results with the super cheap XSE15-8-5k with 6AS7 triodes and paralleled 5687s. Flat down to 10Hz. (Granted I didn't measure distortion that low and expect it to be rather high). The slightly more pricey GSE series are great for the price.
Measurements of a 6AS7 job doing an Edcor XSE25-16-7.6K and later same tubes doing a One-Electron UBT2. $25 vs $110.
One watt into 8ohms. Please ignore low frequency content, the amp was still in progress and had some hum.
As you see the Edcor does have some higher harmonics, likely only due to impedance being 'wrong' for these tubes, but I honestly couldn't hear much difference in the short listening test I did.
Response wise the Edcor was flat 10Hz-40kHz and the One Electron about 7Hz-50kHz.
One watt into 8ohms. Please ignore low frequency content, the amp was still in progress and had some hum.
As you see the Edcor does have some higher harmonics, likely only due to impedance being 'wrong' for these tubes, but I honestly couldn't hear much difference in the short listening test I did.
Response wise the Edcor was flat 10Hz-40kHz and the One Electron about 7Hz-50kHz.
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Looking at the third harmonic I actually think the 25 dB difference is rather big and might be audible.
Just so I'm not misunderstood here. The one electrons are better and worth the extra, but for the money, the Edcors are good to go. The slightly more expencive GSE series are better and it'd be interesting to try them in the same amp.
To follow up on my previous post, I measured the turns ratio of an Edcor CXSE25-8-5K at 24.4 V excitation (as well as 2.44 and 0.244 V). I got 1.000 V out on the secondary (0.100, 0.010 with the lower excitation). Hence, I conclude the turns ratio is 24.4:1. That would make the primary impedance (24.4^2)*8 = 4763 ohm with the specified 8 ohm load. So some 5 % down from the specified 5 kOhm load. Not bad...
~Tom
~Tom
OK, simple low tech experiment. I took one of my CXSE25-8-5K's, attached an 8 ohm resistive load to the secondary, and stuck the primary leads into the wall outlet.
The primary voltage is 122.9 volts. The secondary voltage is 5.04 volts. This gives a turns ratio of 24.385, resulting in a primary impedance of 4757 ohms. Not far off from Tom's numbers.
The primary voltage is 122.9 volts. The secondary voltage is 5.04 volts. This gives a turns ratio of 24.385, resulting in a primary impedance of 4757 ohms. Not far off from Tom's numbers.
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