There was a thread that introduced the Edcor XSE-15-8-5K transformer to the world.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72654&highlight=edcor I tested these and posted the results.
There was also a thread where the 6AV5's were tested and abused.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=6av5
This thread is about what happened when the two meet.
I wired a pair of 6AV5's and a regulated power supply into the same TubelabSE that I had been using for these tests before. The first test was ran at the rated 11 watts dissipation, 300 volts and 35 mA. The amp sounded OK but kind of subdued. In my usual style I turned up the power. Much to my surprise they starded to exhibit the death glow at about 15 watts. This is not what I saw before. These were NOS tubes, not dirty old ones. So I found the old tubes that I had used before. OK now I can crank up the power. I was running 350 volts at 60 mA with no glow. They sounded nice, good bass, clear sparkling mids and crystal clear highs. I listened for two hours with a wide variety of music. It sounded good, but not as good as the Edcor with the 300B.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72654&highlight=edcor I tested these and posted the results.
There was also a thread where the 6AV5's were tested and abused.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=6av5
This thread is about what happened when the two meet.
I wired a pair of 6AV5's and a regulated power supply into the same TubelabSE that I had been using for these tests before. The first test was ran at the rated 11 watts dissipation, 300 volts and 35 mA. The amp sounded OK but kind of subdued. In my usual style I turned up the power. Much to my surprise they starded to exhibit the death glow at about 15 watts. This is not what I saw before. These were NOS tubes, not dirty old ones. So I found the old tubes that I had used before. OK now I can crank up the power. I was running 350 volts at 60 mA with no glow. They sounded nice, good bass, clear sparkling mids and crystal clear highs. I listened for two hours with a wide variety of music. It sounded good, but not as good as the Edcor with the 300B.
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In one of the previous threads someone suggested the 6FW5. I put a pair of these into the amp, and cranked it up to 350 volts 65 mA. No deasth glow, and It rocked. This was the best sounding combo yet. Tried triode, UL, and pentode connections. The results were as expected. My next experiment will be to try cathode feedback.
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Interesting work, for which my thanks. And also thanks for the tip on your website about Harbor Freight voltmeters. I bought ten.
In this and a few other experiments, you've blatantly exceeded the Vg2(max) voltage. Now, I use screen drive in my amp, originally motivated by the low rating of my sweep tube outputs. Any temptation I had to rationalize running the screen higher (i.e., in "normal" triode mode at, say, 400-600V) was quashed by the manufacturer ratings of triode mode, always at voltages well below limits. Thus I have zero experience in that usage and am curious about the experience of others.
So my question is, which sweep tubes have you used long enough to get a rough idea that no harm is occuring by flouting the ratings? Clearly you're stressing these more than I would, so if it's working for you...
In this and a few other experiments, you've blatantly exceeded the Vg2(max) voltage. Now, I use screen drive in my amp, originally motivated by the low rating of my sweep tube outputs. Any temptation I had to rationalize running the screen higher (i.e., in "normal" triode mode at, say, 400-600V) was quashed by the manufacturer ratings of triode mode, always at voltages well below limits. Thus I have zero experience in that usage and am curious about the experience of others.
So my question is, which sweep tubes have you used long enough to get a rough idea that no harm is occuring by flouting the ratings? Clearly you're stressing these more than I would, so if it's working for you...
SY:
I have abused the 6AV5's because I have a lot of them, and they are cheap. I just picked up about 15 more at the Orlando Hamfest, for $3 or $4 each. I have not run any of these for more than a few days so I don't know what the long term reliability will be like. I plan to try them long term in a triode or UL amp soon.
I have operated a pair of 6LW6's in triode mode at about 385 volts (400 volt supply 15 lost in OPT) for several months without any issues. These tubes have a 275 volt rating. They still look, and work like new. I have a large (about 75 lbs) box full of assorted sweep tubes to experiment on, so further experiments will happen sooner or later.
6146's really don't like having their screen voltage pushed, neither do 6AQ5's or 6BQ5/EL-84.
Fuling:
I was surprised to see the red glow of death appear in the NOS pair of RCA's at 15 watts. I dug up the pair of tubes that I used for the original test, and re - tried them. They both were able to take about 30 watts with NO glow visible even with the room lights off. One of these was a GE and the other was a Dumont. They were of obviously different internal construction. Upon further investigation I found at least 5 different internal constructions for the 6AV5GA. The NOS RCA's that I tested had large slots in the radiating fins at the point where the fins attach to the plate. This would limit the thermal conductivity. What were they thinking? I also found RCA's without these slots. I have some Sylvanias, and several other flavors, I will stress test them as soon as I get time. I will be out of town for most of this weekend again.
I also want to get amp specs for the above experiments in triode, UL, and pentode modes.
I have abused the 6AV5's because I have a lot of them, and they are cheap. I just picked up about 15 more at the Orlando Hamfest, for $3 or $4 each. I have not run any of these for more than a few days so I don't know what the long term reliability will be like. I plan to try them long term in a triode or UL amp soon.
I have operated a pair of 6LW6's in triode mode at about 385 volts (400 volt supply 15 lost in OPT) for several months without any issues. These tubes have a 275 volt rating. They still look, and work like new. I have a large (about 75 lbs) box full of assorted sweep tubes to experiment on, so further experiments will happen sooner or later.
6146's really don't like having their screen voltage pushed, neither do 6AQ5's or 6BQ5/EL-84.
Fuling:
I was surprised to see the red glow of death appear in the NOS pair of RCA's at 15 watts. I dug up the pair of tubes that I used for the original test, and re - tried them. They both were able to take about 30 watts with NO glow visible even with the room lights off. One of these was a GE and the other was a Dumont. They were of obviously different internal construction. Upon further investigation I found at least 5 different internal constructions for the 6AV5GA. The NOS RCA's that I tested had large slots in the radiating fins at the point where the fins attach to the plate. This would limit the thermal conductivity. What were they thinking? I also found RCA's without these slots. I have some Sylvanias, and several other flavors, I will stress test them as soon as I get time. I will be out of town for most of this weekend again.
I also want to get amp specs for the above experiments in triode, UL, and pentode modes.
There was an article in Glass Audio back in 1999 that demonstrated a 90 WPC P-P amp using 26LW6's. (It seems to have dissapeared from their web site, I am sure that I have a PDF somewhere if you want it.) That got me thinking about "testing" some of these. I performed my usual extreme testing. I can't find my original paperwork yet, but I remember getting 140 Watts RMS at clip at 1KHz. I was limited by the 80 Watt OPT on the low frequency side. I was using a SS bridge rectifier on a 575 volt 500 VA industrial transformer for a B+ of 700 to 750 volts. I was using my Knight regulated supply for the screen and driver voltage, but I don't remember what the actual voltages were. I was using conventional G1 drive and fixed bias.
This was one of my early Tubelab prototyping system experiments which was taken appart rather quickly to do other experiments. I didn't have it together for long, and I was thinking guitar amp when I built it, so it was never optimized for sound quality. I tend to torture these type of things pretty good (full power for an hour straight, play my guitar through it at the severe clipping level) so if it was a weak design it would have blown up.
Most of my recent experiments have been SE. I will get back to P-P some time. 6LW6's seem to be pretty tough, but there again are about 4 different flavors, and they are not all the same.
This was one of my early Tubelab prototyping system experiments which was taken appart rather quickly to do other experiments. I didn't have it together for long, and I was thinking guitar amp when I built it, so it was never optimized for sound quality. I tend to torture these type of things pretty good (full power for an hour straight, play my guitar through it at the severe clipping level) so if it was a weak design it would have blown up.
Most of my recent experiments have been SE. I will get back to P-P some time. 6LW6's seem to be pretty tough, but there again are about 4 different flavors, and they are not all the same.
150 watts from 2 tubes, tell me more. Plate voltage, current, load impedance, G1 voltage? What is the quiescent G2 DC voltage, and required drive level. I have a lot of these tubes to experiment with, and I have limited experience with screen drive, but this sounds like a great place to start.
Maybe I am too blond, but I don't see any way to include a file using the email button. I hesitate to put my email address in a piece of text anywhere, but it can be found on my website (a JPEG). That stops most of the evil spammers. Send me an email, and I will reply with the PDF. It is almost 600K in size.
The article has some history on the tubes, and claims that the 6LW6 is the octal equivalent to the 6LF6.
Maybe I am too blond, but I don't see any way to include a file using the email button. I hesitate to put my email address in a piece of text anywhere, but it can be found on my website (a JPEG). That stops most of the evil spammers. Send me an email, and I will reply with the PDF. It is almost 600K in size.
The article has some history on the tubes, and claims that the 6LW6 is the octal equivalent to the 6LF6.
In my amp, Vg1 is zero (tied directly to the cathode), Vg2 is about -10V, zero signal current is 3mA per tube, 1250 ohms plate to plate, 800V B+. It requires a PILE of drive, 150VRMS or so; it's possible I could get more out at the risk of the output tubes, since the driver poops out first. Despite the very low idle current, the output tubes run very linearly at low power, no visible crossover distortion.
I'll pop you an email about the paper, thanks!
I'll pop you an email about the paper, thanks!
Well, I thought about this for about 10 seconds, and then I opened up some 6AV5 boxes. One of the tubes in the original test is a Dumont brand. Upon further inspection these are made by Sylvania. I have 6 distinct types of 6AV5 tubes. Two types of RCA's (with and without the slots in the radiating fins), two GE's, a Raytheon, and the Sylvania. I have just finished torturing (I mean testing) each type. The dissipation figures that I use are total (plate and screen) tube current times actual plate to cathode voltage. All tubes were tested at 300 volts triode strapped unless otherwise noted. All of this testing was done at very low volume (milliwats), this is worst case for dissipation. Sherri has freinds over, so I can't crank it up loud anyway.
The slotted RCA's start glowing at about 15 watts, this is only slightly above the 13.5 watt rating. These all have the newer style lettering on the boxes and two letter date codes.
The non slotted RCA exhibited no visible redness at 30 watts. At this plate dissipation, I could see the screen wires begin to glow if operated at 325 volts. No glow was seen at 275 volts and 30 watts. These tubes all have taller glass and 1963 date codes. 4 tubes tested.
The Raytheon (I only have one here) started to glow at 23 watts.
There are two types of GE's. The newer ones have plates with rounded corners that look identical to those in the 6FW5 which carries a 21.6 watt (total) rating. I tested 2 of these. One showed a slight redness, only visible with the room lights off at 27 watts. The other showed no color at 30 watts.
The older GE's have the smallest plates and smallest envelope of any of the tubes tested, but they seem happy at 27 watts, and just show slight redness at 30 watts. 4 tubes tested, all the same.
The Sylvanias are clearly the best of the bunch in the overload department. When you push them hard enough to get them glowing the entire radiating fin glows evenly, no hot spots. I got a few minutes to listen to the Dumonts at 315 volts, 80mA, which is the sweet spot for the Edcor transformers. They do sound nice, but I am not quite raedy to trade in my (Chinese) 300B's. There is no visible at this level, and it takes 30 watts to see any. 2 Sylvanias, and 2 Dumonts tested. Both Dumonts have the Sylvania EIA code 312 on them. The included photo was taken at 315 volts and 130mA, this is 41 watts.
Considering that a 6B4 is only good for 15 watts, I would use any of these tubes except the slotted RCA. Guess which one I have the most of?
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Thanks for the info!!
Hey, great stuff! I have changed my mind and have decided to try a parallel single ended 12av5 amp, maybe three tubes per channel. I've got mostly Sylvania tubes, so it looks like I got lucky
Any recommendations on good transformers for this sort of load? How about some cheap ones to experiment with? Thanks and keep up the torture on those sweep tubes!
Isaac
Hey, great stuff! I have changed my mind and have decided to try a parallel single ended 12av5 amp, maybe three tubes per channel. I've got mostly Sylvania tubes, so it looks like I got lucky
Any recommendations on good transformers for this sort of load? How about some cheap ones to experiment with? Thanks and keep up the torture on those sweep tubes!Isaac
Oh one more thing, that sure is one purty picture of a glowing tube Which Edcor transformer are you using?
Duh, never mind, it's right in your first post... Sounds like a great transformer to experiment with and not sweat it too much if you screw up and fry them... I'll probably order some later on. Do you see any that they make that would be OK for paralleled 6av5 tubes?
Isaac
Which Edcor transformer are you using?Duh, never mind, it's right in your first post... Sounds like a great transformer to experiment with and not sweat it too much if you screw up and fry them... I'll probably order some later on. Do you see any that they make that would be OK for paralleled 6av5 tubes?
Isaac
3 tubes in parallel, that would want a load of 1.5 to 2 k ohms. The only Edcors that come close are the CXSE25 series. They are $75 each. Another possible choice is the One Electron UBT1 for $85. I have not tried either transformer. I have used One Electron UBT-3's in 300B amps and they work very well. The Edcors are the only ones with UL taps.
If two tubes would provide enough power and you wanted to save money, you could get the 16 ohm version of the same transformer and run it with an 8 ohm load.
SY planted an idea in my head that I can't shake, so I am going to try 2 6AV5's in P-P with screen drive. I have all of the parts, so I am going to make some sound, or some smoke. I don't know which yet!
If two tubes would provide enough power and you wanted to save money, you could get the 16 ohm version of the same transformer and run it with an 8 ohm load.
SY planted an idea in my head that I can't shake, so I am going to try 2 6AV5's in P-P with screen drive. I have all of the parts, so I am going to make some sound, or some smoke. I don't know which yet!
A couple more noob questions...
Does the trioded 6av5 actually respond like a 6b4g? I ask because when I look at the data sheets for the 6b4g it specifies an output impedance of around 2.5k instead of the 5k that you're using. Are you using this transformer just because you have them there and you wanted to see what they'd do despite being the wrong spec, did you do something else to make it a good match, or am I making a basic newbie error? I can't find any info on 6av5 in triode mode other than it is supposed to pass for a 6b4g, so is that a good place to start? Thanks!
Isaac
Does the trioded 6av5 actually respond like a 6b4g? I ask because when I look at the data sheets for the 6b4g it specifies an output impedance of around 2.5k instead of the 5k that you're using. Are you using this transformer just because you have them there and you wanted to see what they'd do despite being the wrong spec, did you do something else to make it a good match, or am I making a basic newbie error?
I can't find any info on 6av5 in triode mode other than it is supposed to pass for a 6b4g, so is that a good place to start? Thanks!Isaac
The trioded 6AV5 = 6b4 story has been around for a long time. It has surfaced many times over the years, and I always dismissed it as an urban legend. The story is that Phillips or Sylvania built some triode wired 6AV5's with 6B4 pinouts to satisfy a military contract. Well if you look at the "tube gallery" on the Angela instruments web site (www.angela.com) you can see a picture of one, so the legend is true. This means that the tubes were similar enough to be interchangeable IN THE ORIGINAL APPLICATION. There is no way that the two can ever be identical.
Someone posed the question in the original thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=
So I decided to try this out. During those tests I used a One Electron UBT-3 transformer which presents a 3K ohm load. I believe that this is about optimum, but I never did load VS power VS distortion testing. I did swap back and forth between the 6AV5 and the 6B4, and they are a lot more similar than I would have thought.
Then there was another thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72654&highlight=
This thread was about an $18 SE output transformer. The lowest impedance that this transformer comes in is 5K ohm so I bought two of those. I tested them with 45's and 300B's.
Then I was at the Orlando hamfest where I got a box full of 6AV5's for $3 each. Well, I just connected all of this stuff together because it was sitting on my bench asking to be tested. I have been listening to this amp for over a week now, and I like the sound of it, so I have been listening instead of testing. I still don't know how much power or distortion I am getting. I will get around to testing sooner or later.
I think I am going to get another pair of the SE transformers with a 16 ohm secondary. This will give the tube a 2.5K load with an 8 ohm speaker.
SY's comments have got me building a P-P 6AV5 amp with screen drive. I'll get a pair of the cheap Edcor P-P transformers for this one too, but the order will have to wait until I find out what the optimum load for this amp is.
Someone posed the question in the original thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=
So I decided to try this out. During those tests I used a One Electron UBT-3 transformer which presents a 3K ohm load. I believe that this is about optimum, but I never did load VS power VS distortion testing. I did swap back and forth between the 6AV5 and the 6B4, and they are a lot more similar than I would have thought.
Then there was another thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72654&highlight=
This thread was about an $18 SE output transformer. The lowest impedance that this transformer comes in is 5K ohm so I bought two of those. I tested them with 45's and 300B's.
Then I was at the Orlando hamfest where I got a box full of 6AV5's for $3 each. Well, I just connected all of this stuff together because it was sitting on my bench asking to be tested. I have been listening to this amp for over a week now, and I like the sound of it, so I have been listening instead of testing. I still don't know how much power or distortion I am getting. I will get around to testing sooner or later.
I think I am going to get another pair of the SE transformers with a 16 ohm secondary. This will give the tube a 2.5K load with an 8 ohm speaker.
SY's comments have got me building a P-P 6AV5 amp with screen drive. I'll get a pair of the cheap Edcor P-P transformers for this one too, but the order will have to wait until I find out what the optimum load for this amp is.
Thanks for the info! I'm back to trying a 12av5 SE amp as my first scratch build since I have them and they're really cheap. Your dissipation tests really piqued my interest, but I want to make sure that I get the right transformers, even if they are cheap If 2.5k is indeed the ideal load for a single tube, I might pony up the money for the 25watt speced transformers from them. Keep us in the loop with your experiments, good data on audio usage of sweep tubes can be difficult to get and I appreciate anything I can get
Isaac
If 2.5k is indeed the ideal load for a single tube, I might pony up the money for the 25watt speced transformers from them. Keep us in the loop with your experiments, good data on audio usage of sweep tubes can be difficult to get and I appreciate anything I can getIsaac
As I said earlier I have about 75 pounds of sweep tubes, and more in boxes that I haven't gone through yet. I will try more experiments as time permits, but I don't have much time right now.
I may have not explained it fully in my earlier posts, but If you intend to build an amplifier and keep it around for a while, don't push the tubes too hard unless you plan to change them often. Transistors just blow up when you push them too hard. Tubes can be operated above the maximum dissipation rating at the expense of shorter life. It is not uncommon for a guitar player who plays 4 or 5 two hour shows a week to need new tubes in six months or less. NOS tubes seem to live longer than many current production tubes due to better vacuum, and most sweep tubes were over designed due to the severe service they were in.
6AV5's, 12AV5's and 25AV5's are cheap (for now) so if you plan to push them hard get some spares. My rule of thumb is to turn off the room lights and look for red spots on the plate, and glowing grid wires. Back off the bias until this goes away.
Some of these tubes seem more sensitive to voltage than others. I am using a variable power supply so I can watch the current as I turn up the voltage. All triode connected sweep tubes will have a point where the current starts to rise quickly. Operation at or above this point could cause an uncontrolled runaway condition. I beleive this is because we are way above the screen voltage rating. This happens at about 295 volts on some 6AV5's while others are happy with 350 volts.
If you are going anywhere near this you should put a 100 (or 125) milliamp fuse in the cathode leg. It may save your transformers if a tube fails.
I may have not explained it fully in my earlier posts, but If you intend to build an amplifier and keep it around for a while, don't push the tubes too hard unless you plan to change them often. Transistors just blow up when you push them too hard. Tubes can be operated above the maximum dissipation rating at the expense of shorter life. It is not uncommon for a guitar player who plays 4 or 5 two hour shows a week to need new tubes in six months or less. NOS tubes seem to live longer than many current production tubes due to better vacuum, and most sweep tubes were over designed due to the severe service they were in.
6AV5's, 12AV5's and 25AV5's are cheap (for now) so if you plan to push them hard get some spares. My rule of thumb is to turn off the room lights and look for red spots on the plate, and glowing grid wires. Back off the bias until this goes away.
Some of these tubes seem more sensitive to voltage than others. I am using a variable power supply so I can watch the current as I turn up the voltage. All triode connected sweep tubes will have a point where the current starts to rise quickly. Operation at or above this point could cause an uncontrolled runaway condition. I beleive this is because we are way above the screen voltage rating. This happens at about 295 volts on some 6AV5's while others are happy with 350 volts.
If you are going anywhere near this you should put a 100 (or 125) milliamp fuse in the cathode leg. It may save your transformers if a tube fails.
tubelab.com said:
No problem, I think I speak for everyone on this board when I say that we appreciate you sharing whatever time you can spare. With any luck, I'll be able to add to the knowledge pool before too long...
Good advice, I'll probably do the fuse thing even if I'm not going close to those numbers. Hopefully it'll protect them in case a tube fails either due to it being driven too hard or my stupidity... In any case, I was figuring I'd back off a bit, I prefer designs run well within the limits of the tube. I have half a mind to make this a present to someone and i want to make sure that they could put in any 12av5 and have it work well. Plus, it's nice to be able to set up an amp and forget it for years... With the dissipation numbers you were posting, it sounds as though I could back off from 10-12 watts of output power to 6-7 and keep the tube around for a long time to come. I don't think the miniscule difference between 7 and 10 watts is a good enough reason to shorten tube life
Isaac
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