Cheap SE output transformers

[karma]

Originally posted by tubelab.com
I was looking up the prices of the popular audio tubes being tested above on several web sites, when I found a bold statement. On Antique Electronics Supply's web site there is an add for a "6L6GC China Coke bottle" for $7.95, followed by the statement "We could not blow up this tube, no matter how hard we tried." Now this seems like a challenge to me. I dug through my collection and found a pair of tubes that look like theirs, except they have the Ruby Tubes logo screened onto them.

I put these into the amp and proceeded to turn up the juice. If you look carefully in the attached picture you can see the voltmeter on the power supply ix maxed at 400 volts. The digital meter on the right shows 110 mA. This is 44 watts per tube. There is an even glow on the plates, and the tube is stable with no hint of runaway. It ran at this current for an hour with no problems. I turned it down to 80mA and there is no glow. I am sure that I could blow up this tube if I really tried, but they are really tough.

I have been listening to these for 3 days and find them to be the best overall compromise. In triode they are almost as good as the EL-34's and in UL they are close to the 6550's.

Overall the Edcors have surprised me with their sound and price. I am working on a new amp design using these transformers. The idea is to make a low cost SE amplifier that sounds almost as good as a TubelabSE.

have you tested the old 807's in se? and if so what did you think.

[jleaman]

Karma,

Shoulden't those be in a box on there way to meeee

[tubelab.com]

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.

[wrenchone]

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?

[tubelab.com]

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.

[wrenchone]

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....

[vt_229]

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.

[John L]

Let's bump this one up, since it needs an update.

Has George tried the CXSE Edcor line yet? I haven't seen any mention of this anywhere yet.

[wrenchone]

Actually, people have mentioned the more expensive Edcors in other threads - try a search.

[John L]

Originally posted by wrenchone
Actually, people have mentioned the more expensive Edcors in other threads - try a search.

Yes, but has George tested them in relation to the other OPTs he has used? I have not seen anything about this on his site so far.

Perhaps you can point me to the treads that go into this upper leverl OPT?