Banned
Joined 2002
I have not tested their CXSE transformers, because I have found several good transformers in this price range. Good $18 transformers are real hard to find!
I bought 10 pairs of Transcendar 300B transformers for about $60 each on E-bay (still available), and I have not used them all up yet. These are good transformers. I have also used some custom transformers that I got from Electra-Print. They were excellent transformers, the best that I have tried, and they were $100 each at the time ( the price has gone up slightly). I have also used One Electron SE transformers with good success.
I will probably try the CXSE transformers and the Edcor power transformers after I have finished refining the Simple SE amp designs (there are two). I don't have much time for tube stuff right now (long work days), but there are some comparative transformer tests planned, and some have already happened. I have several pages of test data scattered throughout my computer and on paper. It is slowly getting organized for an upcomming update to my web page.
I have tested some 807's, but not in this amp design, or with the $18 Edcor transformers yet. I have a box full of WWII vintage 807's, and a large box of WWII vintage 1625's. They will find their way into an amp design sooner or later. I find that most of my 807's sound very similar to 6L6GB's (tested in this amp) or 6BG6's of the same vintage. It has been discussed as to whether these tubes are all the same, with valid points on both sides. I believe that the ones that I have all have the same guts in them. I have taken some of them apart and find that their construction is identical.
I bought 10 pairs of Transcendar 300B transformers for about $60 each on E-bay (still available), and I have not used them all up yet. These are good transformers. I have also used some custom transformers that I got from Electra-Print. They were excellent transformers, the best that I have tried, and they were $100 each at the time ( the price has gone up slightly). I have also used One Electron SE transformers with good success.
I will probably try the CXSE transformers and the Edcor power transformers after I have finished refining the Simple SE amp designs (there are two). I don't have much time for tube stuff right now (long work days), but there are some comparative transformer tests planned, and some have already happened. I have several pages of test data scattered throughout my computer and on paper. It is slowly getting organized for an upcomming update to my web page.
I have tested some 807's, but not in this amp design, or with the $18 Edcor transformers yet. I have a box full of WWII vintage 807's, and a large box of WWII vintage 1625's. They will find their way into an amp design sooner or later. I find that most of my 807's sound very similar to 6L6GB's (tested in this amp) or 6BG6's of the same vintage. It has been discussed as to whether these tubes are all the same, with valid points on both sides. I believe that the ones that I have all have the same guts in them. I have taken some of them apart and find that their construction is identical.
I just nailed down a pair of the Transcendar 5k 100ma transformers on the web, no doubt earning a little hate... These will be interesting with a pair of triode strapped 6550s or with a pair of 6HV5As driving an 8 ohm load with the 4 ohm tap. How much of a flogging can these things take, and how would you compare the sound quality with the Electra-Print or the $100 Hammonds?
I have not tried the Transcendar 5K transformers yet. They are relatively new. I tested the 3K version directly against a 3K One Electron of the same size and power rating. The sound was very similar. If I remember correctly the Transcendar had better dynamics, and the One Electron tested better for high frequency response (outside the audio range). I am at work now and the data is at home.
I have not tried any of the $100 Hammonds yet, although I am thinking about the big boys (1642SE) for an 833A amp when I get the time to build it.
As for "stress testing", the most that I have fed any of these transformers was a 6LW6 triode strapped at 110 mA and 400 volts. I was using the 8 ohm tap with a 4 ohm load to present a 1.5 K load to the tube. Under these conditions I was getting 15 watts at .8% distortion. This combination had the best bass and transients of any thing I tested at the time. I was drive limited so there was some power left behind. I will try this again when I have more time. ( this was mentioned in the 6AV5GA thread)
I briefly tried 6HV5's in the same amp and could not get them to work right. I only have two of these, so I did not spend much time. My amp can not do positive grid voltage without modification, and my B+ was limited to 400 volts, so I could not get much current.
I have not tried any of the $100 Hammonds yet, although I am thinking about the big boys (1642SE) for an 833A amp when I get the time to build it.
As for "stress testing", the most that I have fed any of these transformers was a 6LW6 triode strapped at 110 mA and 400 volts. I was using the 8 ohm tap with a 4 ohm load to present a 1.5 K load to the tube. Under these conditions I was getting 15 watts at .8% distortion. This combination had the best bass and transients of any thing I tested at the time. I was drive limited so there was some power left behind. I will try this again when I have more time. ( this was mentioned in the 6AV5GA thread)
I briefly tried 6HV5's in the same amp and could not get them to work right. I only have two of these, so I did not spend much time. My amp can not do positive grid voltage without modification, and my B+ was limited to 400 volts, so I could not get much current.
The curves published for the 6HV5A look very similar to the ones I plotted for the 6CD6GAs - high Rp, will need positive bias to get significant Ip at lower plate voltage. Since the 6HV5A is so blasted sensitive, it shouldn't take much positive bias to get things cooking. What was so attractive about these tubes was the hefty 35W plate dissipation rating, the high cathode current rating, and the high gain. I have a fair number of the GE version of this tube - the plates are truly monstrous. The secret to getting these guys to play will probably be to use positive bias at 600-700V B+, or go whole hog and use 1.5-2kV, hoping that the output transformers have a decent hipot rating.
First things first, though. I'm still working on my 6CD6GA SE amp using the Hammond 125ESE output iron. Right now, I'm debugging the bias, HV regulator, and soft start circuits - no big problems so far. Once I get this and the main HV up, I'll start on wiring the actual amp circuits. Slow and steady does it - I haven't had much spare time lately, and I don't want to get nailed by 400V....
First things first, though. I'm still working on my 6CD6GA SE amp using the Hammond 125ESE output iron. Right now, I'm debugging the bias, HV regulator, and soft start circuits - no big problems so far. Once I get this and the main HV up, I'll start on wiring the actual amp circuits. Slow and steady does it - I haven't had much spare time lately, and I don't want to get nailed by 400V....
Edcor Opts
yup after a few beers the sound gets sweeter, but the o scope was sober, I think, and it liked them too. The guy at www.funwithtubes.com tested more expensive edcor and was impressed with the sound and range, he scoped them and indicated they exceeded his expectations. But that does not constitute a comparison.
yup after a few beers the sound gets sweeter, but the o scope was sober, I think, and it liked them too. The guy at www.funwithtubes.com tested more expensive edcor and was impressed with the sound and range, he scoped them and indicated they exceeded his expectations. But that does not constitute a comparison.
I got a set of these and tested them in 2006. I compared them to the Hammond 1628SE's. The results are here:
http://www.tubelab.com/Output_Transformers.htm
The transformers sat around for a while and were used in several temporary experiments. Late last year they were used to troubleshoot a 300B TubelabSE. They sounded so nice that I decided to build myself a similar amp. Personal circumstances have kept the amplifier from being finished. It still looks like the one shown here in post # 7.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68216&highlight=vt225
http://www.tubelab.com/Output_Transformers.htm
The transformers sat around for a while and were used in several temporary experiments. Late last year they were used to troubleshoot a 300B TubelabSE. They sounded so nice that I decided to build myself a similar amp. Personal circumstances have kept the amplifier from being finished. It still looks like the one shown here in post # 7.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68216&highlight=vt225
TubeLab I think you contribute some of the most interesting information on this site your test results and methods are great. I'm amazed at the pictures of the Coke bottle Chinese 6L6's with the plates glowing. I've used some of those in guitar amps and they did sound quite good. They didn't have a lot of power but in an old Fender used for blues styles they were tough to beat. I also used some Chinese 6L6's that were straight bottle. I used to get them through Audio Glassic about 12-15 years ago they were awesome sounding and I never had a failure. I don't think either of these tubes is really available in quantity any more.
I am a newbie to the diyAudio forum.
I am building Alex Gendrano's KT88 SE tube amplifier. I have a pair of Hammond 1645 PP output trannies and was thinking of using them instead of Hammond 1628SE. The 1645PP has a primary impedance of 5K ct and multiple taps. I emailed Hammond for advice and got a response that "it would result in poor performance" - not a comprehensive answer! Is the distinction between SE and PP designs real? There are some low end universal trannies available. Any thoughts from the forum members about my substitution proposal? Any tips on wiring the 1645s is welcome - they are slightly different from the rest of the Hammond PP range.
I have ordered some Edcors but they are on a 4 week delivery; the factory is busy - the stimulus is working!!
Thanks
I am building Alex Gendrano's KT88 SE tube amplifier. I have a pair of Hammond 1645 PP output trannies and was thinking of using them instead of Hammond 1628SE. The 1645PP has a primary impedance of 5K ct and multiple taps. I emailed Hammond for advice and got a response that "it would result in poor performance" - not a comprehensive answer! Is the distinction between SE and PP designs real? There are some low end universal trannies available. Any thoughts from the forum members about my substitution proposal? Any tips on wiring the 1645s is welcome - they are slightly different from the rest of the Hammond PP range.
I have ordered some Edcors but they are on a 4 week delivery; the factory is busy - the stimulus is working!!
Thanks
Kibs said:
PP transformers are not really designed for SE use, due to the unbalanced DC current that flows in SE, causing core saturation. SE transformers have a gapped core to facilitate SE use. IIRC, tubelab George (and probably many others) have dissassembled PP transformers and used tape to gap the laminations for SE use.
The design of the core on a PP OPT is not equipped to handle the net DC current through the primary...it lacks an air gap. In a PP application, the tube bias current flows through the primary winding from the center tap to the ends, which cancels out any magnetic flux in the core due to this DC current. In an SE application, this DC current flows from one end of the primary to the other, which will saturate the core resulting in poor performance. Manufacturers get around this by introducing an air gap in the core. This causes other negative effects, but these are compensated for in the design of the OPT.
You can modify a PP OPT to work in a SE application by completely disassembling the core (including all of the laminations) and rearranging them such that a gap is possible. Most people use a few sheets of paper to set the gap and then re-stack the core.
Russ
You can modify a PP OPT to work in a SE application by completely disassembling the core (including all of the laminations) and rearranging them such that a gap is possible. Most people use a few sheets of paper to set the gap and then re-stack the core.
Russ
The 1645s are P-P transformers, so they don't have the gap necessary for SE operation. You can fiddle around and introduce some bucking bias on 1/2 of the primary that may let you run SE, but you need a proper supply and current source to make this work. This has been discussed in other threads at this site, so a search would bear some fruit. Me, I'd just wait for the real SE transformers, or buy a pair on Ebay (the little Transcendar 5ks are nice 10w transformers) as stopgaps.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.