avguytx Posted October 21, 2015 Share Posted October 21, 2015 I don't own a pair of Heritage speakers at the moment but am very interested in building a "stereo" version of this in a single chassis. Aren't the Epic CF series a little overrated on their stipulated effiiciency rating? My CF-3's say they're 100db @ 1watt/1meter but I've ready where many think that's exaggerated. Ultimately I'm going to build my own Belle's as they never come up around here for a reasonable amount. Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted October 21, 2015 Share Posted October 21, 2015 Hey Maynard, what's the damping factor with 8 ohm speakers? 5? I think the 6y6 triode Rp is roughly 900 around that operating point? Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted October 21, 2015 Author Share Posted October 21, 2015 Hey Maynard, what's the damping factor with 8 ohm speakers? 5? I think the 6y6 triode Rp is roughly 900 around that operating point? "XX" you know your stuff! I just calculated the Rp and got about 1k, and then took a real quick measurement of the output impedance which is about 2.5 ohms. So, the damping factor into 8 ohms would be 3.2 of course. There are absolutely no issues with controlling the woofers. Maynard Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted October 22, 2015 Share Posted October 22, 2015 Hello Maynard, thanks for getting back to me. I think the 6Y6 is a fascinating valve, that thing pulls a good amount of heater current! I need more but I would have thought the DF would be higher. How did you do your measurement? Did you measure and compare the change in voltage against the change in load. Measured data is better than calculated theory data so I trust your numbers. I just thought it might be lower due to the 5k:8 transformer. 5k:8 has a turns ratio of 25:1 impedance ratio 625:1 With Rp = 1k I get 1000 / 625 = 1.6 and 8 / 1.6 = 5 So an estimated dampening factor of 5 is what I came up with. Your measurements might indicate the Rp is slightly higher than what was calculated from plate curves. For the output Z to be 2.5 the Rp would then be around 1k5. I have zero experience with the 6Y6 and there is not much info out there so I am just trying to get as much data as possible out there on how this valve performs as a triode for finals in a single ended class A amp. BTW you can call me JP, I feel like xx is too feminine from a biological standpoint (23rd chromosome) Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted October 22, 2015 Author Share Posted October 22, 2015 BTW you can call me JP, I feel like xx is too feminine from a biological standpoint (23rd chromosome) JP, you're the man!!! Regarding the output impedance, I do use a voltage comparison method into 2 different loads (in this case 4 and 8 ohms). This comes up quite a bit, so one of the nearby NJ ham crowd prepared a youtube video on 2 different methods which is excellent: Yes, the 6Y6 is an excellent tube all around. Even used in a SEP application, it's really nice in its ability to generate a decent amount of power with a very low plate/screen voltage. In fact, I may consider a future "Little QT" build using it that way. Maynard Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted October 22, 2015 Share Posted October 22, 2015 No sir, you are the man!!! Great job with the mono's..............I am jealous. Quote Link to comment Share on other sites More sharing options...
FloridaBoy Posted October 23, 2015 Share Posted October 23, 2015 (edited) Very nice Maynard! The 6Y6 is a fine tube. Edited October 23, 2015 by FloridaBoy Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted October 23, 2015 Share Posted October 23, 2015 (edited) I am not sure if Maynard had this in mind when designing these but I have been looking at the 6Y6 a little closer and it seems like the 6Y6 looks very similar to a 2A3, well a 6.3v indirectly heated version. Both plate resistance and transconductance are very close, the 6Y6 is slightly higher hence the higher mu but all that means is it's slightly easier to drive. Other than that the devices electrically perform similarly. Maynard how would you compare the Sweeties sonically to similar 2A3 amps? For those of you interested in the allure of SET amps and don't want to pay outrageous money for 2A3 tubes I would seriously consider the 6Y6. Not to mention you don't have to worry about all the extra complexity of powering the DHT's filament properly. Edited October 23, 2015 by xxJPMxx Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted October 23, 2015 Author Share Posted October 23, 2015 JP, after reading your post I pulled up the plate curves for the 2A3 and was very surprised to see the similarity you mentioned. I had no idea! In fact, I have never bothered with DHT designs as I've always considered them to be more of a nuisance than they are worth (especially in regard to the filament supply issues). The only one I've heard is the 300B in a design a friend created about 10 years ago. I wasn't impressed at all (neither was he)- it could have been the design, the tube, or both. In any case, we may have now found the "poor man's 2A3." Better stock up before the word gets out and they start costing a fortune!!!Maynard Quote Link to comment Share on other sites More sharing options...
thebes Posted October 26, 2015 Share Posted October 26, 2015 Looks like another great build from the small and inexpensive is the way to go genius of our own Maynard. I own a custom designed SEP of Maynard's, using some amps from a console pull, which was totally redone by Maynard after I screwed up the build. I also have built a modified version of his "Little Gem" SEP from last year using Edcor OPT's and a different tube lineup. The sound from both is absolutely stellar, especially considering the price. Only a couple of caveats. They require a bit of creativity if your using vinyl , especially LOMC, or have a really big room and need to drive them hard. Obviously efficient speakers are a basic requirement and not a problem if you own anything od decent size built by Klipsch. For the money for a build you can't go wrong, if you want to explore the world of tubes and build your own this is the way to go. Don't worry if you get stuck on figuring out a part of have a question or two, Maynard not only welcomes such questions he lives for them. He's a teacher at heart whose bringing new life to the "obsolete" radio designs of yore. Quote Link to comment Share on other sites More sharing options...
Guest David H Posted October 26, 2015 Share Posted October 26, 2015 Very nice. Dave Quote Link to comment Share on other sites More sharing options...
avguytx Posted October 26, 2015 Share Posted October 26, 2015 So are Epic CF series sensitive enough? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted October 27, 2015 Share Posted October 27, 2015 So are Epic CF series sensitive enough? Have you tried the CF-3 with the Magnavox 6BQ5/EL-84 push-pull console amplifier? If you have, and the speaker's had boogie factor, (good sound) then the triode strapped 6Y6 Sweetie Pie amplifier should work. One thing maybe to be concerned about is how low the impedance swing on the CF-3 would be. Another thing is to just try it and find out. Quote Link to comment Share on other sites More sharing options...
avguytx Posted October 27, 2015 Share Posted October 27, 2015 Yes, it and the Stromberg Carlson both do quite a good job on them but the low end on those amps are limited to around 45 or 50Hz because of the transformers. But the upper range of those amps when redone are quite surprising. Quote Link to comment Share on other sites More sharing options...
Fjd Posted October 30, 2015 Share Posted October 30, 2015 (edited) 1) use of inexpensive, readily available, tubes which were originally designed for radio service, and which offer extreme long-term reliability. Maynard I decided to start my "work-in-process" area for this amplifier and with some careful shopping found this selection of tubes for about $7.50 each. There are even cheaper examples, but couldn't resist the milspec 6SJ7 and 6Y6GT tubes. I thought the RCA gray glass 6Y6 ST's were nice looking and couldn't pass them up. In addition, I'm not sure how much impact the driver tube will have on sound; however, I thought the glass / nickel base Hytrons may be an interesting option. I don't think Hytron made any of their own tubes; however, since I'm not familiar with the 6SJ7, I'm not sure who would have manufactured the re-badge for them. . Edited October 30, 2015 by Fjd Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted October 30, 2015 Author Share Posted October 30, 2015 Those tubes sure look nice! Can't wait to see your amp (s) when completed, and read your impressions about the sound. Feel free to ask any questions! Maynard Quote Link to comment Share on other sites More sharing options...
Fjd Posted October 30, 2015 Share Posted October 30, 2015 (edited) Hammond output xfmrs tend to be a bit on the expensive side- going with Edcor can save some money. I have never heard the latter; however William, and others, has reported that they sound wonderful. Maynard I have a pair of Electra-Print single-ended design transformers [5K, 65ma., 10w, 6 Ohms] that I picked up cheap from eBay while 'audio-picking' that are currently in my parts collection that look like they would match up well for this amplifier. Here are a couple of links to 8 Ohm (although I generally like 6 Ohm to split the difference between 8 Ohm & 4 Ohm when only one option is available) Edcor transformers if anyone is interested in other less expensive options. My Pete Millett DCPP "Engineer's Amplifier" has Edcor transformers that seem to do very well in that amp. XSE10-8-5K: 10W, single ended tube output transformer for 5K Ohms to 8 Ohms $17.22 https://www.edcorusa.com/xse10-8-5k GXSE10-8-5K: 10W, single ended tube output transformer for 5K Ohms to 8 Ohms $27.42 https://www.edcorusa.com/gxse10-8-5k Edited October 31, 2015 by Fjd Quote Link to comment Share on other sites More sharing options...
mike stehr Posted October 31, 2015 Share Posted October 31, 2015 The Edcor for 17 bucks has a frequency response of 70Hz-18kHz at minus one decibel. Minus 3 decibels would be lower yet, a dumb guess on my part would around 50Hz? The one for 30 bucks has a low end roll-off of 50Hz at 1 decibel, lower yet at -3dB. I know these are good options on the cheap, but may be lacking in lower bass once the circuit is lashed up. Then again, maybe not... The big 87 dollar 25 watt single-ended Edcor OPTs advertise 20Hz-20kHz frequency response. I know that 200 bucks is a bit of cash, but still not a bad deal at all considering the price of output transformers nowdays. Another brand, (Transcendar?) is reasonably priced option from what I understand... Quote Link to comment Share on other sites More sharing options...
Fjd Posted October 31, 2015 Share Posted October 31, 2015 (edited) The Edcor for 17 bucks has a frequency response of 70Hz-18kHz at minus one decibel. Minus 3 decibels would be lower yet, a dumb guess on my part would around 50Hz? The one for 30 bucks has a low end roll-off of 50Hz at 1 decibel, lower yet at -3dB. I know these are good options on the cheap, but may be lacking in lower bass once the circuit is lashed up. Then again, maybe not... The big 87 dollar 25 watt single-ended Edcor OPTs advertise 20Hz-20kHz frequency response. I know that 200 bucks is a bit of cash, but still not a bad deal at all considering the price of output transformers nowdays. Another brand, (Transcendar?) is reasonably priced option from what I understand... I saw that and was going to link the $87 model too, which I would consider if I didn't have the Electra-Prints, but also noticed that the Hammond 125CSE data sheet shows 100 Hz. - 15 Khz (+/- 1db max. ref. 1 KHz). I don't have any experience either with the Transcendar; however, here is the website link. http://www.transcendar.com/2.html Transcendar 5 watt option, 5K to 8 ohms, Frequency Response: 20 Hz to 80 kHz, Maximum DC Bias Current: 65 mA, Primary DC Resistance: 350 ohm, Primary Inductance: 20 H, Part Number TT-005-OT , $45.00 each Transcendar 5 watt option, 5K to 4 & 8 ohms, Frequency Response: 20 Hz to 100 kHz, Maximum DC Bias Current: 65 mA, Primary DC Resistance 370 ohm, Primary Inductance: 20 H, Part Number TT-104-OT, $50.00 each . Edited October 31, 2015 by Fjd Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted October 31, 2015 Share Posted October 31, 2015 I recently went with Transcendar for my latest build. As soon as I finish I will give a review, they look to be built well I went with the 10 watt 100mA 3k:8, $150 a pair is a good deal for the bandwidth. Quote Link to comment Share on other sites More sharing options...
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