I'm looking for something in the 10-15W range, 20Hz-20KHz or better, with a primary around 2.5 to 3.5K, preferably with a screen gap, and an 8 ohm secondary. I'd like to be able to switch between a big pent/tet in UL and a more traditional SE tube like a 6B4G.
The only halfway-reasonably priced OPT's I've been able to find like this are made by James, and they run $145 a pair. This isn't amazingly expensive but it seems like someone (maybe Edcor, I sent them a formal quote request) could do better. What do you think? Do you know of any OPT's like this that beat James for price? Besides, I don't like the look of those round cans
For very low-power use, I assume that Edcor's low-end variety would be OK, after reading the big post where TubeLab does a bunch of testing. A 1626 at .75W, yes. A 6EM7 in SE at around 1.5-2W, yes. A 6L6GC/EL34 in UL, though? A 300B? Probably not.
The only halfway-reasonably priced OPT's I've been able to find like this are made by James, and they run $145 a pair. This isn't amazingly expensive but it seems like someone (maybe Edcor, I sent them a formal quote request) could do better. What do you think? Do you know of any OPT's like this that beat James for price? Besides, I don't like the look of those round cans
For very low-power use, I assume that Edcor's low-end variety would be OK, after reading the big post where TubeLab does a bunch of testing. A 1626 at .75W, yes. A 6EM7 in SE at around 1.5-2W, yes. A 6L6GC/EL34 in UL, though? A 300B? Probably not.
Exactly. The little guys work great at low powers. You can get 25 Hz to 40 KHz at 2 watts. As the power levels increase the frequency response does not change, but saturation sets in, and the distortion goes up rapidly for low frequencies and high powers. Saturation distortion sounds particularly nasty if it happens often.
It is a matter of Physics that saturation effects are related to the size of the core, regardless of who makes the transformer. If you want disco sized bass from a SE tube amp, you need big transformers. The best in this regard are the big Hammonds (I use the 1628SEA) followed closely by the Big Edcors. Both of these will produce bass that rivals a 50 WPC solid state amp from a KT88 (slightly overbiased). These are 10+ pound transformers. Their large cores cost some eficiency and high frequency response.
When I use the small Edcor transformers with my small (7 inch woofer) Yamaha speakers, I can run power levels up to 10 watts without hearing serious distortion. Why? The Yamaha speakers have a frequency response that is virtually nonexistent below 60 Hz, AND the impedance rises below 70 Hz. This takes the load off of the transformer right where it falls apart, so the transformer doesn't have to work hard to produce frequencies that it can't. It is interesting to watch the speaker cones with this amp playing Pink Floyd at high volumes. There are some bass notes that cause severe cone movement, but almost no sound. The scope shows some saturation distortion, but I don't hear it! If I take the same setup into the living room, and connect it to the big speakers (15 inch woofer) I must turn the volume down to about 10 % of the power that I was running on the Yamahas to avoid nasty distortion. These speakers are 10 db more efficient, so it is still plenty loud.
What does this mean to the listener? It means that the small Edcors will sound great in the right setup, with the right speakers. I have tried the pair that I have in several different amplifiers, with several different speaker systems. Where would I recommend them?
1) A low powered amp. My pair have found their current home in a SimpleSE that uses 6V6 tubes. This amp makes 1.5 to 2 watts. I have not run a frequency response test, but I would be surprised if it didn't do 25 Hz to 40 KHz at full power. The Edcors sound better in this amp than ANY OTHER TRANSFORMER THAT I HAVE TRIED in this amp.
2) An amp that does not need to produce much power below 80 Hz. If you have a subwoofer, and an active crossover that keeps the low bass out of the amp, these would be great. They may work well with speakers that can't produce the low bass.
3) A moderate powered amp that feeds super efficient speakers so that the average power level is low. The amp may still distort if it is called upon to produce 5 watts at 30 Hz, but this may not happen often.
I have not tried James transformers yet. I almost ordered a pair for my latest cathode follower project, but I was offered a pair of Eastern Audio transformers by a fellow poster for a really low price. 600 ohm transformers are not easy to find. I got the Easterns, but I will probably get something better after I get the design all scienced out. Probably James.
I have used One Electron and Transcendar transformers with good results in 300B and 6L6-EL34-KT88 amps. The Transcendars are the best transformers for the money. I have them in my Industrial amp. These test out inferior to the Hammond 1628SEA's at low frequencies, but they just sound better. The One Electrons sound very similar, but they cost more. Both are 6 pound transformers.
All right. Sounds like a small SE amp is in order. I'm thinking a 6EM7/6GL7, or maybe a 6BL7/6BX7/6DN7 driven by a 6N1P and one of the triodes or something. I have zero cash at the moment, but my Cerwin Vegas back at home are 98dB efficient so ~2W should hopefully be OK, even for the pounding-bass minimal techno that I listen to. The Cerwins are good down to 25Hz, so it'd be interesting to play around with some test tones and see how low a tiny SE amp could go 
FWIW, I built a 6EM7 SE amp that I absolutely love and am using Hammond 1225ESE trannies with Fostex 93db speakers. They are great sounding but could use a little bit more grunt at the lower frequencies. I can hear the 30-40Hz tones but I they are pretty rolled off. I too was looking for better OPT and did look at the ones from James. Also due to not having too much $$$ to spend on my hobbies they seem the best option at the time.
Then the Edcors came into the picture. The LF specs on the Edcors are better then the Hammonds (70Hz vs 100Hz) and they are cheaper too. Would the extra 30Hz make me happier for only $40 but still wonder what it would sound like knowing I could go down to 20Hz for a few bucks more? To date, I have not made a decision yet on whether to get the Edcors or splurge on the James and be done with it. My suggestion is if you are just experimenting get the Edcors, but if you want to be done with it, get the James.
Then the Edcors came into the picture. The LF specs on the Edcors are better then the Hammonds (70Hz vs 100Hz) and they are cheaper too. Would the extra 30Hz make me happier for only $40 but still wonder what it would sound like knowing I could go down to 20Hz for a few bucks more? To date, I have not made a decision yet on whether to get the Edcors or splurge on the James and be done with it. My suggestion is if you are just experimenting get the Edcors, but if you want to be done with it, get the James.
Hey RockysDad,
If you haven't tried cathode feedback through the secondaries of the 125ESE's, you really should try it. On the 6EM7 amp I used it on, I actually ran the cathode current through the secondary of the 125ESE's, but Tubelab reports that just connecting the cathode bypass cap to the secondary works just as well. You might even be able to reduce primary impedance for more power and still get cleaner bass.
Kyle
If you haven't tried cathode feedback through the secondaries of the 125ESE's, you really should try it. On the 6EM7 amp I used it on, I actually ran the cathode current through the secondary of the 125ESE's, but Tubelab reports that just connecting the cathode bypass cap to the secondary works just as well. You might even be able to reduce primary impedance for more power and still get cleaner bass.
Kyle
At least with my small speakers, I could not hear much difference in the bass between the 125CSE and the XSE15-8-5K. The Edcor just sounded better overall, but the difference is not huge.
I will test the performance of the amp after two things happen. I must finish my current project. The deadline is 12 days away. The person that I loaned the amp to must give it back. So far my requests for its return are met with "how much do you want for it?"
Is there any triode of similar nature to the 2/6A3/6B4G that isn't as expensive? I'm thinking around 12W plate dissipation?
I have eight 6S19P's but they're very hard to drive and I don't know what impedance I'd use them at... dissipating 9 out of 11 watts might yield around 2W, right? could a single 6SL7 in totem-pole drive one of these tubes?
I have eight 6S19P's but they're very hard to drive and I don't know what impedance I'd use them at... dissipating 9 out of 11 watts might yield around 2W, right? could a single 6SL7 in totem-pole drive one of these tubes?
Try a triode wired 6AV5GA. Any of them can dissipate 12 to 15 watts. The good ones over 20 (Sylvanias). The screen grid rating is 175 volts, but I have never met one that complained at 300 volts, and most will work at 350. They can be found for $3 or $4.
See the following threads for more info:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=6av5
http://www.diyaudio.com/forums/showthread.php?s=&threadid=74650&highlight=
See the following threads for more info:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=6av5
http://www.diyaudio.com/forums/showthread.php?s=&threadid=74650&highlight=
Any ideas on how to do this? Right now my cathode is sitting at about 140V due to this being a DC coupled amp. Not real easy finding a 1200uF cap at that voltage. I haven't really looked for one yet but it might be pretty big. If I could get more power and more clearer bass, I would be one happy camper. Can't throw a party with only .8W...
http://www.the-planet.org/6EM7.html
For cathode feedback try the following:
You don't need 1200uF. The 47uF specified in the original schematic is sufficient to get 1.2Hz at -3dB. I've found that smaller film caps sound much better than large value electrolytics - especially in the bass. You could use a 30-47uF @ 250-400V Solen or similar. Not too costly.
Just connect one lead of the cathode bypass cap to the cathode (pin 3) and the other lead to the white secondary lead of the 125ESE. The connection to ground is now through the OPT secondary. If you are using electrolytics, observe the polarity. I assume you are using the yellow secondary to give you 5K:8 ohms. Try it that way first and see how it sounds. Then try the white secondary to drop the primary to 2.5K. You might think that's a little low for the 6EM7's 750 ohm plate resistance, but the cathode feedback will compensate for it and you will get a little more power. You only get 5K by the turns ratio anyway - inductance isn't increased to support the higher impedance.
You don't need 1200uF. The 47uF specified in the original schematic is sufficient to get 1.2Hz at -3dB. I've found that smaller film caps sound much better than large value electrolytics - especially in the bass. You could use a 30-47uF @ 250-400V Solen or similar. Not too costly.
Just connect one lead of the cathode bypass cap to the cathode (pin 3) and the other lead to the white secondary lead of the 125ESE. The connection to ground is now through the OPT secondary. If you are using electrolytics, observe the polarity. I assume you are using the yellow secondary to give you 5K:8 ohms. Try it that way first and see how it sounds. Then try the white secondary to drop the primary to 2.5K. You might think that's a little low for the 6EM7's 750 ohm plate resistance, but the cathode feedback will compensate for it and you will get a little more power. You only get 5K by the turns ratio anyway - inductance isn't increased to support the higher impedance.
Let me get this straight, do I just connect the (-) of the cap to the white lead of the secondary and still have the yellow (8 ohms) (+)and black (-) leads going to the speakers?
Now in this test both the cap (-) and the speaker (+) will be connected together. Is this correct?
Question... Is this negative or positive feedback? I always thought that we would use the black wire for feedback to the cathode for negative feedback (sorry I do not know what the difference is). I think one will add and the other would subtract from the outputs????
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