Hey - thanks, guys!
Have I got homework to do or what? I really appreciate all of the help. The info on the AM radio ccts from wa2ise is very interesting and I will refer to it often.
Sheldon, thanks for the link to the 6BM8 thread - this will be a goldmine for me.
Bandersnatch; could you please explain "LTP from the triodes, and U-L rig the pentode section across ~10k a-a."
Jess
Have I got homework to do or what? I really appreciate all of the help. The info on the AM radio ccts from wa2ise is very interesting and I will refer to it often.
Sheldon, thanks for the link to the 6BM8 thread - this will be a goldmine for me.
Bandersnatch; could you please explain "LTP from the triodes, and U-L rig the pentode section across ~10k a-a."
Jess
sure...
Make a two stage amp. One long-tail-pair circuit built around the triode sections. WIth one grid grounded, and output from the two plates. It is a voltage amp, and phase-splitter all in one.
With the pentode sections, use a 10,000 ohm anode-anode Ultra-Linear output TX. Run the pentode sections in PP, with the g2 attached to the U-L taps.
Better?
cheers,
Douglas
Make a two stage amp. One long-tail-pair circuit built around the triode sections. WIth one grid grounded, and output from the two plates. It is a voltage amp, and phase-splitter all in one.
With the pentode sections, use a 10,000 ohm anode-anode Ultra-Linear output TX. Run the pentode sections in PP, with the g2 attached to the U-L taps.
Better?
cheers,
Douglas
Hey-Hey!!!,
The 10k was a guess. Depending on how you do the NFB, you can probably do less. My RCA 23 does not have that valve's curves. Judging by its gm, and mu-g1g2, lower might be better. 6k6 maybe. If you are U-L, it is far more tolerant. Pentode is quite particular about its load and bias point. The move in 'triode' direction( of the anode curves ) afforded by U-L is a good thing.
The characteristics are somewhat similar to the 6L6, and those are happy with 6k6 a-a.
cheers,
Douglas
The 10k was a guess. Depending on how you do the NFB, you can probably do less. My RCA 23 does not have that valve's curves. Judging by its gm, and mu-g1g2, lower might be better. 6k6 maybe. If you are U-L, it is far more tolerant. Pentode is quite particular about its load and bias point. The move in 'triode' direction( of the anode curves ) afforded by U-L is a good thing.
The characteristics are somewhat similar to the 6L6, and those are happy with 6k6 a-a.
cheers,
Douglas
Thanks Bandersnatch.
I am going to put my head down for a couple of days and see if I can come up with a schematic for this lil' beastie (even if it's wrong, it is a great learning experience). When I come back with it, I hope you guys will tear it apart and tell me why it's wrong
See you all in a couple of days
Jess
I am going to put my head down for a couple of days and see if I can come up with a schematic for this lil' beastie (even if it's wrong, it is a great learning experience). When I come back with it, I hope you guys will tear it apart and tell me why it's wrong
See you all in a couple of days
Jess
Hi Tubelab,
That's an interesting design, good to see that he at least considers running all the parts well within their safe operating parameters.
Seems he's trying to get the most power out of a pair of tubes, which looks to require strong grid drive and therefore a very complex circuit. The small grid bias resistance on the outputs should help tube life.
I'd rather go with 4 output tubes in a mode that requires less drive. The Dynaco Mark VI comes to mind with 4 - 8417 output tubes:
http://www.geocities.com/vintageaudio/markvi.jpg
Interesting that you mention these and it's too bad that they're unreliable.
Seems to me that the 7581 would be a good choice in PP parallel since a pair provide 70W plate dissipation and should offer 100W output with the right OT. Also, the heater requirements are low. A quad of 6CA7s as a comparison only provide 50W of plate dissipation, on the other hand they have twice the transconductance lowering the drive requirements.
Pete B.
That's an interesting design, good to see that he at least considers running all the parts well within their safe operating parameters.
Seems he's trying to get the most power out of a pair of tubes, which looks to require strong grid drive and therefore a very complex circuit. The small grid bias resistance on the outputs should help tube life.
I'd rather go with 4 output tubes in a mode that requires less drive. The Dynaco Mark VI comes to mind with 4 - 8417 output tubes:
http://www.geocities.com/vintageaudio/markvi.jpg
Interesting that you mention these and it's too bad that they're unreliable.
Seems to me that the 7581 would be a good choice in PP parallel since a pair provide 70W plate dissipation and should offer 100W output with the right OT. Also, the heater requirements are low. A quad of 6CA7s as a comparison only provide 50W of plate dissipation, on the other hand they have twice the transconductance lowering the drive requirements.
Pete B.
tubelab.com said:
If you're looking for low drive requirements, and high power the 813 ought to make your list. I have one on the way, and it looks like about +/- 60V of g1 drive( and no grid current from going positive ).
They'll deliver me ~80W with a Class A indifference to what the PS is doing. The 100W single plate dissipation rating does have something to do with this. The 50W cathode in another way to support high power. High current availablility. The big sweep tubes all have ~20W heaters.
I am continually puzzled by the DIY-ers building AB1 high power designs. Why would one expect anything but commercial, AB1, high power sound? If you're doing it yourself, do it better, and go for the best. It is troublesome enough to build an amp, I think I will remove the built in limits to the best of my ability *FIRST*, and then start playing with it.
cheers,
Douglas
They'll deliver me ~80W with a Class A indifference to what the PS is doing. The 100W single plate dissipation rating does have something to do with this. The 50W cathode in another way to support high power. High current availablility. The big sweep tubes all have ~20W heaters.
I am continually puzzled by the DIY-ers building AB1 high power designs. Why would one expect anything but commercial, AB1, high power sound? If you're doing it yourself, do it better, and go for the best. It is troublesome enough to build an amp, I think I will remove the built in limits to the best of my ability *FIRST*, and then start playing with it.
cheers,
Douglas
Hi,
I've got a matched pair of brand new Tungsram PL509's, with sockets.
I've got an outputtrafo with the folllowing parametres: Raa=1,9K, P=120W. I've got a mains trafo too, with secondaries: 2*170V (340V), 40V (heather and for -Ug1), 6,3V (for pre tubes).
I've got every parts (case, pot's, ECC tubes, sockets, puffer condensers, etc...) to build a 120W PA amp.
But I need an information (because there aren't datasheet available for PL509's as audio output tubes): what is the recommended Ug2? I think 150-200V... But what are you thinking?
Thanks, best regards
I've got a matched pair of brand new Tungsram PL509's, with sockets.
I've got an outputtrafo with the folllowing parametres: Raa=1,9K, P=120W. I've got a mains trafo too, with secondaries: 2*170V (340V), 40V (heather and for -Ug1), 6,3V (for pre tubes).
I've got every parts (case, pot's, ECC tubes, sockets, puffer condensers, etc...) to build a 120W PA amp.
But I need an information (because there aren't datasheet available for PL509's as audio output tubes): what is the recommended Ug2? I think 150-200V... But what are you thinking?
Thanks, best regards
Yikes! As a collector and restorer of old round screen color TV's I have to suffer now with not only Hams who use transmitters with 6JE6's in them but now McIntosh owners as well? If only vintage TV's used these vintage TV TUBES they would still be cheap and plentiful.
If you need 350 watts it makes a lot more sense to use four 811A's, or better yet, tubes powerful, enough that only a pair are required. That way when one goes south it doesn't take out the whole bank like dominos with it from overload. I can easily see 'accidents' depleting the world's stock of 6JE6's at an unecessary rate because this is a really clever idea once upon a time that has turned around to bite us in the 4SS.
The good news for owners of this Mc are that production 6CA7's are now more plentiful and cheaper than NOS sweep tubes and could be easily used with minor modifications. Enginering at the handwaving level here only. I didn't open a tube manual.
If you need 350 watts it makes a lot more sense to use four 811A's, or better yet, tubes powerful, enough that only a pair are required. That way when one goes south it doesn't take out the whole bank like dominos with it from overload. I can easily see 'accidents' depleting the world's stock of 6JE6's at an unecessary rate because this is a really clever idea once upon a time that has turned around to bite us in the 4SS.
The good news for owners of this Mc are that production 6CA7's are now more plentiful and cheaper than NOS sweep tubes and could be easily used with minor modifications. Enginering at the handwaving level here only. I didn't open a tube manual.
bit us in the 4SS...LOL
There are all sorts of silly little bits of info that will allow the Truly Dedicated to build cheaply with sweep tubes.
One I'll share: late procuction 6LW6 by Sylvania look just like 6LF6. Same bottle shape, same plate srutucture. Given the Sylvania/Philips/ECG propensity for commonizing...I am not suprised.
The early GE 6LW6 is distinctly different.
They did this same thing with 6L6GC/7581A/6BG6GA as evidenced by Mike Marx's experimentation. Look at the notes at SND Tubes.
cheers,
Douglas
There are all sorts of silly little bits of info that will allow the Truly Dedicated to build cheaply with sweep tubes.
One I'll share: late procuction 6LW6 by Sylvania look just like 6LF6. Same bottle shape, same plate srutucture. Given the Sylvania/Philips/ECG propensity for commonizing...I am not suprised.
The early GE 6LW6 is distinctly different.
They did this same thing with 6L6GC/7581A/6BG6GA as evidenced by Mike Marx's experimentation. Look at the notes at SND Tubes.
cheers,
Douglas
The 6LW6 is my favorite sweep tube, in fact there is one glowing on my bench right now, in a CCS parafeed experiment. See the thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=67437&pagenumber=4
I started buying these on Ebay about 5 years ago when you could get them for under $10 each, often $5. The 6LW6 was the last of the big octal sweep tubes. The 6LF6 was the compactron offspring of the 6LW6. I have seen 5 distinctly different versions of 6LW6, with 2 different bottle sizes. There are 2 different GE versions. It seems that they went through a learning curve to figure out the supplemental heat radiating fins on the plate. The good ones (both flavors of GE) can dissipate far greater than the specified 40 watts without complaint. A push - pull pair can put out 140 watts of audio easily.
Certain sweep tubes, the 6JE6/6LQ6 in particular were used in the manufacture of illegal citizens band radio amplifiers in the 70's and 80's. Some of these (the varmint 500) used 10 6JE6's. The design, and implementation were poor, causing these amplifiers to eat tubes at an accelerated rate. With 10 tubes per amp, this is why the 6JE6 is getting rare. GE even made a 12 volt filament version for this market the 8950, try to find one of those!
Yes, people had 500 watt CB amplifiers in their cars. The power supplies put out too much noise for mobile HiFi use, already tried it.
McIntosh and simple should not be used in the same sentence!
http://www.diyaudio.com/forums/showthread.php?s=&threadid=67437&pagenumber=4
I started buying these on Ebay about 5 years ago when you could get them for under $10 each, often $5. The 6LW6 was the last of the big octal sweep tubes. The 6LF6 was the compactron offspring of the 6LW6. I have seen 5 distinctly different versions of 6LW6, with 2 different bottle sizes. There are 2 different GE versions. It seems that they went through a learning curve to figure out the supplemental heat radiating fins on the plate. The good ones (both flavors of GE) can dissipate far greater than the specified 40 watts without complaint. A push - pull pair can put out 140 watts of audio easily.
Certain sweep tubes, the 6JE6/6LQ6 in particular were used in the manufacture of illegal citizens band radio amplifiers in the 70's and 80's. Some of these (the varmint 500) used 10 6JE6's. The design, and implementation were poor, causing these amplifiers to eat tubes at an accelerated rate. With 10 tubes per amp, this is why the 6JE6 is getting rare. GE even made a 12 volt filament version for this market the 8950, try to find one of those!
Yes, people had 500 watt CB amplifiers in their cars. The power supplies put out too much noise for mobile HiFi use, already tried it.
McIntosh and simple should not be used in the same sentence!
tubelab.com said:
Looks like they were quite adept at complicating thinsgs. From the Bi-filar wind on the MC30 output TX, and on up to the Tri-filar wind on the MC75 and what I'll bet is a "five-filar" in the MC3500.
I think I will leave that output for later...just the wire is going to be quite expensive. I'll bet it does rated power all the way across its rated BW...unlike the current practice of the SE amp makers seem to adopt for playing the Spec's Game. Oh well...if one reads the rules it is easier to play.
cheers,
Douglas
Tubelab,
So what you are saying is someday my 21" round screen color TV's from the end of their era around 1966 like the RCA CTC-20 are going to become valuable if they contain a good 6JE6.
BTW, I went to your fine website yesterday for the first time and have been studying its contents. Your painstaking commitment to R&D there is obvious. Good for you. I'd like to discuss some of your findings at some point.
I have a couple of dozen NIB 6JN6 compactrons which beg an audio amp application I think. A pair of these are used very cleverly in a so called OTL circuit switching at low RF frequencies with a ferrite cored 'output xfmer' by Mr. Berning. I've heard that this is supposed to be a very fine amplifier but have never had the opportunity to see or hear one.
I also have a lot of NIB 12DQ6 looking for a project. I have no interest in making a bunch of portable, live chassis transformerless B&W TV sets.
My precious limited stock of NIB ST shape 6BG6's will be used to maintain my fleet of 1940's TV receivers.
Rob
So what you are saying is someday my 21" round screen color TV's from the end of their era around 1966 like the RCA CTC-20 are going to become valuable if they contain a good 6JE6.
BTW, I went to your fine website yesterday for the first time and have been studying its contents. Your painstaking commitment to R&D there is obvious. Good for you. I'd like to discuss some of your findings at some point.
I have a couple of dozen NIB 6JN6 compactrons which beg an audio amp application I think. A pair of these are used very cleverly in a so called OTL circuit switching at low RF frequencies with a ferrite cored 'output xfmer' by Mr. Berning. I've heard that this is supposed to be a very fine amplifier but have never had the opportunity to see or hear one.
I also have a lot of NIB 12DQ6 looking for a project. I have no interest in making a bunch of portable, live chassis transformerless B&W TV sets.
My precious limited stock of NIB ST shape 6BG6's will be used to maintain my fleet of 1940's TV receivers.
Rob
I worked in a TV shop during that era. The later RCA's were pretty good TV's, did you ever meet a CTC-5? I was not impressed.
I am not sure just how many of those CB amplifiers are still out there operating, but they definitely used up more than their share of tubes during the CB boom of the late 70's.
I believed at the time that I started the website that I was one of the few "vacuum tube engineers" left. Now that I have found this forum, I found a few more. I have a full time job as an engineer at a high tech electronics facillity, which hasn't left much time for tubes lately. A major update of the web site is comming soon.
As for Mr. Berning's ZOTL circuit, I have not had the opportunity to hear one. I have read his patent, and the idea has merit. I tried a similar idea (the solid state transformer) a few years back, with mixed results. Good sound intermixed with the smell of burnt mosfets. Mosfets have improved greatly since I tried it before, someday I will try again. I haven't yet tried the 6JN6 or the 6JB6, but I think I have some in the warehouse. Someday.
I have played with 6DQ6's, they worked well enough to set aside for future experiments.
I have a few 6BG6's but I have a large box of 807's and a larger box of 1625's. I believe that they are all the same tube, although some believe that the 807 is "special". These were all derived from the 6L6GB, and during WWII they probably all had the same guts. I will definitely build something with these, but I haven't decided what yet.
I am not sure just how many of those CB amplifiers are still out there operating, but they definitely used up more than their share of tubes during the CB boom of the late 70's.
I believed at the time that I started the website that I was one of the few "vacuum tube engineers" left. Now that I have found this forum, I found a few more. I have a full time job as an engineer at a high tech electronics facillity, which hasn't left much time for tubes lately. A major update of the web site is comming soon.
As for Mr. Berning's ZOTL circuit, I have not had the opportunity to hear one. I have read his patent, and the idea has merit. I tried a similar idea (the solid state transformer) a few years back, with mixed results. Good sound intermixed with the smell of burnt mosfets. Mosfets have improved greatly since I tried it before, someday I will try again. I haven't yet tried the 6JN6 or the 6JB6, but I think I have some in the warehouse. Someday.
I have played with 6DQ6's, they worked well enough to set aside for future experiments.
I have a few 6BG6's but I have a large box of 807's and a larger box of 1625's. I believe that they are all the same tube, although some believe that the 807 is "special". These were all derived from the 6L6GB, and during WWII they probably all had the same guts. I will definitely build something with these, but I haven't decided what yet.
i have been following this thread closely, there is a shop here with a truckload of nos sweep tubes!
but they need compactron sockets and novar 9pins, do you know where to get this if at all they still exist?
another question, has anybody tried to run these tubes off interstage transformers, in screen grid drive triode mode?
would like to know what are at stake here.
thanks
but they need compactron sockets and novar 9pins, do you know where to get this if at all they still exist?
another question, has anybody tried to run these tubes off interstage transformers, in screen grid drive triode mode?
would like to know what are at stake here.
thanks
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