The windings may say plate and screen, but there's nothing keeping one from using a depletion mode (or properly bias enhancement mode) mosfet with this guy and moving some air. The only information missing is the rated primary current. I sure as heck can't think of any pentodes I'd want to be using into a 150 ohm load.
When Edcor first started selling to the DIY market I got a pair of XSE 15-8-5K OPT's and a pair of Hammond 125CSE's. They were tested along with some more expensive transformers here:
Budget OPT's
I have used them in several test amps in the years since that page was written. These two transformers are fairly similar in testing and sound performance. The price has increased considerably since then on these and all other OPT's. The obvious difference is that the Edcor has a UL tap but only a single secondary tap. The Hammond has no UL, but multiple secondary taps. The Edcor is still cheaper.
I find that the "15 watt" Edcor and the "8 watt" Hammond are both a bit over rated. Neither will make full power over the entire audio band. Both will handle more than their rated power over a restricted frequency range. I have used the Edcor in a 6V6 SE amp that made 2 WPC and found it to sound extremely nice and made full power from 20 Hz to almost 40 KHz. It will however distort badly at 14 watts below about 80 Hz.
I bought a pair of the bottom of the line (10 watt) P-P transformers and wasn't too impressed. I decided I should have spent $9 extra for the 15 watt flavor.
I have a set of the big guys too. Here I really prefer the Edcor. It just sounds better.
Pete, cathode follower output would be a bad idea since a cathode follower output requires the same load as an plate follower output.
Mr. Kirchoff says that this should be true. In practice it is not always the case. The common cathode configuration has no inherent built in feedback but has gain. The cathode follower has no gain, but has 100% built in feedback which can dramatically lower the apparent output impedance. If the cathode follower configuration is used with a big fat tube with sufficient peak current handling capacity a much lower load impedance is possible for a given distortion level. Of course you can apply a bunch of feedback around the common cathode design and get similar performance for similar gain. I have been able to crank 15 watts from a single 6LW6 pentode with a cheap Easterm Audio 600 ohm OPT. I don't remember the exact load impedance since i was using something below 8 ohms on the secondary. OPT losses were the limiting factor.
Maybe not. Their 25 watt CXSE series now comes in 150 ohm, 300 ohm, 600 ohm, and 1250 ohm favors. We'll see if the P-P versions appear soon.
I ran out of OPT real quick when doing some hybrid amp testing using a pentode and a BJT in "darlington" configuration with the Chinese OPT's. One of these might be the answer.
150 ohms is probably too low for even the biggest sweep tube in cathode follower operation, but maybe OK for two of them. The pair might be bumping into the 25 watt limit though.
Mr. Kirchoff says that this should be true. In practice it is not always the case. The common cathode configuration has no inherent built in feedback but has gain. The cathode follower has no gain, but has 100% built in feedback which can dramatically lower the apparent output impedance. If the cathode follower configuration is used with a big fat tube with sufficient peak current handling capacity a much lower load impedance is possible for a given distortion level. Of course you can apply a bunch of feedback around the common cathode design and get similar performance for similar gain. I have been able to crank 15 watts from a single 6LW6 pentode with a cheap Easterm Audio 600 ohm OPT. I don't remember the exact load impedance since i was using something below 8 ohms on the secondary. OPT losses were the limiting factor.
Maybe not. Their 25 watt CXSE series now comes in 150 ohm, 300 ohm, 600 ohm, and 1250 ohm favors. We'll see if the P-P versions appear soon.
I ran out of OPT real quick when doing some hybrid amp testing using a pentode and a BJT in "darlington" configuration with the Chinese OPT's. One of these might be the answer.
150 ohms is probably too low for even the biggest sweep tube in cathode follower operation, but maybe OK for two of them. The pair might be bumping into the 25 watt limit though.
When you click the datasheet link it shows an impedance of 300 ohms along with a different part number CXSE25-8-300. Change the url manually to http://www.edcorusa.com/Manuals/CXSE25-8-150.pdf and you get the correct sheet. First I thought 150 was a typo but it looks real. Wonder why they don't give any details like inductance and max current?
Thanks for that. I was suspecting the same, nice to hear it from you.
Still an odd-ball OPT. Wonder what's up?
Well, with jfets and mosfets, I could even make use of the ultralinear tap of this tranformer with an all-silicon version of Pete Millett's E-linear amp. I may do one of these just to be contrary, as long as the primary current rating is sufficient for the job. The rough schematic is left as an exercise, but believe me, it ain't all that complicated....
No, I'm not looking for equivalent exactly. Let me rephrase my question. Hammond have two ranges of SE OTs, one is top-end, the other is their economical range. If I'm being stingy (which isn't unusual) then I start looking for even cheaper options. Low and behold I find Edcor who have an even more economical option. But then I wonder if 'I get what I pay for' I must be giving up a lot of sonic performance. So I ask those who may know, do the cheapo Edcor transformers compare with the cheapo Hammond or are they totally crap ? agains, sorry for off-topic, but this thread got me thinking about Edcor for the first time.
Hello Bigun,
I do this DiyAudio for fun. Spending big money in pursuit of ultra quality is not for me but then there is the exception.
I seem to have near equal numbers of Edcor and eletra-Print output transformers in various amplifiers. I would not hesitate putting down miser money for the Edcor’s. I am with George If the target output is 5 watts spend a little more and get the 15 watt name plate GX** series.
I made a sweep tube SET headphone amplifier that I use daily for stress management. I swapped between a pair of custom (I paid the $40 fee) GX** Edcor 5000 : 300 and an Electra Print 8000 : 300 pair. Now a year later the Edcors are still there being used every day. The Electra Prints are slowly being built into the next iteration DHT headphone amplifier.
I feel that the money paid for the Edcors is well spent.
BTW triode strapped 5763’s sound nice with the Electra Print’s
DT
All Just for fun!
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