I bought mine on eBay...it seemed like they had 5 pieces. It's not real clear to me whether they made a small quantity and they were unproven (marketing-wise).
Some have less-than-stellar hf response.
I bought a single 8k primary 10W one, probably for a clean guitar amp someday. Mostly to get one while available.
They don't seem to respond to any technical inquiries.
I think the logo says all product ships from USA or similar...maybe all the tech info is overseas.
Murray
Some have less-than-stellar hf response.
I bought a single 8k primary 10W one, probably for a clean guitar amp someday. Mostly to get one while available.
They don't seem to respond to any technical inquiries.
I think the logo says all product ships from USA or similar...maybe all the tech info is overseas.
Murray
Antek MP-40W66
I bought a pair of the Antek MP-40W66 Output transformers.. I was a little skeptical but figured it's worth a try.. First measurement was using an Audio Precision with a 5.6k ohm resistor between the source and the primary (Plus the internal 50ohms).. The second measurement was using Clio system to check the impedance of the secondary with the Primary shorted by the same 5.6k resistor.. The secondary was a pretty even 7-8 ohms between 20-20kHz.. indicating that the primary is not too far off the 6.6kohm claim. This first look has me thinking these aren't too bad.. Certainly better than an old Sherwood S8000 Output transformer I have lying around (Which is also ~35w/ 6.6kohm) next, I'll be looking at balance in the primary, see what some DC in the primary does etc.. Then I'll hook them up to my test rig. 2x KT120 with plate feedback (So I can get a good even drive and a good look at what the transformer does without loop feedback)
I bought a pair of the Antek MP-40W66 Output transformers.. I was a little skeptical but figured it's worth a try.. First measurement was using an Audio Precision with a 5.6k ohm resistor between the source and the primary (Plus the internal 50ohms).. The second measurement was using Clio system to check the impedance of the secondary with the Primary shorted by the same 5.6k resistor.. The secondary was a pretty even 7-8 ohms between 20-20kHz.. indicating that the primary is not too far off the 6.6kohm claim. This first look has me thinking these aren't too bad.. Certainly better than an old Sherwood S8000 Output transformer I have lying around (Which is also ~35w/ 6.6kohm) next, I'll be looking at balance in the primary, see what some DC in the primary does etc.. Then I'll hook them up to my test rig. 2x KT120 with plate feedback (So I can get a good even drive and a good look at what the transformer does without loop feedback)
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Excited to see your follow up tests!
I've got a SE 2A3 amp using two of their chokes and a power transformer. No complaints on either though I haven't done any testing.
I don't currently have either choke in the "input" position relative to the rectifier, but plan to eventually. Am curious to see how it will perform.
I've got a SE 2A3 amp using two of their chokes and a power transformer. No complaints on either though I haven't done any testing.
I don't currently have either choke in the "input" position relative to the rectifier, but plan to eventually. Am curious to see how it will perform.
Any further reports/measurements on these transformers? The lowest wattage ones they have seem to have pretty nice looking curves, but as others have noted, they don't tell how they were measured, and at what power level. I'm thinking about biting the bullet on the 5K 15W pp model for a build. Don't want to waste my $$ if they are worthless, but there aren't many options with UL taps available in that price range at the moment, so might have to take the chance, rather than wait months on Edcor transformers to be made.
Ok.. What I did was to create a little test rig to see what these transformers could do. (MP-40W66) I used 2X 5881's driven by a 12AU7. Power (400VDC) and bias was provided by a Heathkit IP32 regulated power supply. The circuit could only drive to about 8.8 watts with the 5881's configured as Triodes. Here's the test circuit and 8.8 watt frequency response into 8ohms. This is open loop. No feedback. Some of the rolloff at the bottom is due to my coupling cap and bias circuit which is a hi-pass at about 9.7Hz. -3dB At about 67kHz. Not bad. There's a little resonant glitch visible at about 55kHz.
Here's a comparison of Triode vs UL vs Pentode operation. The Blue Trace is triode operation at about 300mw and is with the 5881 grids being driven directly by the audio precision. This shows the true bandwidth of this transformer in a real situation with perfect AC balance. The other three sweeps show Triode operation at 1 watt, UL operation at 1 watt (Note glitch at 55Khz) and Pentode operation at 1 watt. (FYI. The tubes were biased at 60ma each.) The overall bandwidth suffered as my driver was losing balance above 30kHz.
Distortion. Here's triode, open loop operation at 5watts and 300mw respectively. Again, the loss of balance at high frequencies causing issues with distortion at higher frequencies. The 300mw distortion is quite good. One take away is that there's a fair amount of interwinding capacitance. This is evident by the decreasing bandwidth with different driving conditions. Triode being low Z, UL and then Pentode..
I decided to try and figure out how good these 40 watt transformers were on the low end. To check distortion, I wired two transformers back to back.. Fed the 8 ohm winding of one from a Crown Macro-Tech 600. I checked the THD at 50Watts, 40Watts and 25Watts on the output of the second transformer loaded with 8 ohms. The bottom trace is baseline distortion of the crown at 50 watts output. Keep in mind. The Distortion is a consequence of going through TWO transformers..
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I have a pair of the MP-10W80. Using them for a small amp with P-P 6n15pe tubes in the output.
There are a few issues I have found in my testing.
The two samples measure very different at high frequencies.
One sample has a leakage inductance of 9mH and the 100H primary inductance stays nearly constant from 100hz to 1KHz.
The second sample has 19mH leakage inductance and the 100H primary inductance plummets above 120Hz.
They behave like different transformers so not great for a stereo amplifer. Seems a serious quality control issue to me.
The data sheet states the primary DCR as 128 ohms but both my samples measured about 556 ohms.
The data sheet states the secondary DCR as 0.2 ohms but both my samples measured about 0.6 ohms.
Again that quality control issue.
The nuts were defective on the supplied bolts. Nothing on its own but with the above brings up that quality control issue, again.
I tested the one with the low leakage inductance with P-P 6n15pe tubes in the output. It went pretty well in early testing and the high frequency response is quite good. Not perfect but good workable transformer, you can do much worse with some of the other china suppliers.
With a 1nF-10K ohm Zoble network on the primary and 8 ohms on the secondary the primary impedance becomes almost totally constant out beyond 100K.
This provides nice wide bandwidth and low phase shift in the feedback loop.
I have not had time to test the low frequency power levels or distortion but at 14 watt at 1KHz they are below 0.02% distortion with 20db of feedback.
Not tested the second sample with double the leakage so who knows.
My current feeling is going forward I am going back to simply paying too much for a Hammond transformer as I have found they work very well and are totally constant in quality. The asia sourced stuff is low in cost but pretty disappointing in quality if you are serious about getting it right.
Roger Modjeski always said no to toroidal OPT's. I buy and use Antek PS transformers at times but not OPT's. Hammond is a really good source for OPT's especially their 125C to 125G series. No end bells so best installed underneath the chassis. Must remember Hammond rates their OPT's at full power and Edcor does not say nor provide data sheets.