Home |
Search |
Today's Posts |
#1
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Hi, Vacuumlanders.
Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g Cheers, Roger |
#2
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Engineer wrote:
Hi, Vacuumlanders. Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g Cheers, Roger I bought a couple of 6AS7's but did not yet build an amp with them. I think it would be cool to have a push-pull tube amp in one envelope. Regards, Sal |
#3
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Roger,
The 6080 (and it's close kin, the 6082) have a claim to fame in the audio world: OTL! (Output TransformerLess). There is an excellent example of this in Terman's "Radio Engineer's Handbook", Mcgraw-Hill, 1954. The idea is to take advantage of the low plate resistance exhibited by this tube, and stack several in series-parallel to directly drive a loudspeaker. Best regards, Ernst |
#5
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Engineer scribbled;
"Engineer" wrote in message oups.com... Hi, Vacuumlanders. Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g Cheers, Roger John Stewart designed two PP amps using 6AS7/6080 family of tubes using A boot-strap driver....GC |
#6
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
On Feb 17, 1:54 pm, "Engineer" wrote:
Hi, Vacuumlanders. Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) Yes, I had a stereo amp breadboarded up with two 6AS7's in each channel. OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) 3,000 ohms was the impedance I used. is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g I used 270 volts on the plates and a twenty volt dropping resistor common to both cathodes. The grids were directly coupled to a negative bias supplied by a 6SN7, this was power by a 270 volt negative power supply. The 6AS7's require alot of drive signal. The pre-amp was a quad op amp(a LF347?) The adjustable bias was obtained by a 5,000 ohm potentiometer between the cathode and the return of the 6SN7's. To get more power I had one triode in the same envolope cooling as the other was heating. I used a power transformer as an output transformer and it sounded pretty good if I recall correctly. Nice and bassy. Cheers, Roger |
#7
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
in article , Engineer
at wrote on 2/17/07 1:54 PM: Hi, Vacuumlanders. Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g Cheers, Roger John Stewart is very knowledgeable about using this tube for an amplifier. The RCA tube manual had a 6080 OTL circuit that was also without a power transformer. I think I'd pass on that one . . . There are a ton of 6AS7 circuits that could sub the 6080, e.g. an OTL circuit from the 2/90 issue of Glass Electronics, etc. Win de Haan designed what looks like a nice hybrid 6AS7G amp using a long-tail phase stage and an E88CC driver stage; the OPT was 3.4K @ 25W. Specs on this one a THD @ 1W = 0.08% 5W = 0.21% 10W = 0.26% GAIN = 20 dB Damping = 13x Feedback - 0 dB! He calls it "6AS7G Push-Pull Amplifier" - 5965 & E88CC based driver stage. Some of the other "problems" with the 6080 series include bad matching of sections and high amperage filament draw. You can find out Wim's contact info with Google or e-mail me. Jon |
#8
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Thanks for all the good info. It mIght just be worth a try, i.e.
protoype one channel on an old tube chassis with a bench reg. P/S. I trust I'll be able to solve the drive requirements. Cheers, Roger |
#9
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
On Feb 17, 9:53 pm, Jon Yaeger wrote:
in article . com, Engineer at wrote on 2/17/07 1:54 PM: John Stewart is very knowledgeable about using this tube for an amplifier. The RCA tube manual had a 6080 OTL circuit that was also without a power transformer. I think I'd pass on that one . . . There are a ton of 6AS7 circuits that could sub the 6080, e.g. an OTL circuit from the 2/90 issue of Glass Electronics, etc. Win de Haan designed what looks like a nice hybrid 6AS7G amp using a long-tail phase stage and an E88CC driver stage; the OPT was 3.4K @ 25W. Specs on this one a THD @ 1W = 0.08% 5W = 0.21% 10W = 0.26% GAIN = 20 dB Damping = 13x Feedback - 0 dB! He calls it "6AS7G Push-Pull Amplifier" - 5965 & E88CC based driver stage. Some of the other "problems" with the 6080 series include bad matching of sections I adjusted the bias so that it idled at 80% of the 13 watts maximum plate disapation. and high amperage filament draw. Very true, 2.5 amps per tube, ten amps for four tubes. You can find out Wim's contact info with Google or e-mail me. Jon- Hide quoted text - - Show quoted text - |
#10
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Engineer wrote: Hi, Vacuumlanders. Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g Cheers, Roger You can set up a PP pair of class AB1 6080 or aka 6AS7 with RL about 1k, a-a and Ea = 200V and if the Pda of the two tubes = 40W, then you get about 10Watts of clean power, or about 100Vrms a-a into the 1k, and gain at about 1.8, so you need about 30Vrms at the grid which is none more than for 6550 in triode. 3k is to high, and the Vswing will be limited by the Ea, which cannot be much above 200V because the tube just doesn't like it, it tends to run away with current if the Ea is too high no matter what the applied grid bias voltage is. The peak Ia available is VERY high for a tube, and ppl have used a quad of 6080 for a basic OTL amp, and Atmasphere makes OTL with lots of 6AS7 as a commercial example. Its also possible to series connect the 6AS7 and use a cap coupled OPT which is a line voltage speaker tranny, Altronics of Western Aust make a toroidal one which I thought would work with the series PP. But a good use is the circlotron circuit with a low Z load on the primary. Two 200V floating supplies are needed. Some toroidal mains transformers are OK to use because with say 240V : 2 x 35V windings you have 240 : 35 with both secs paralleled, giving TR = 6.86, ZR = 47:1 = 376 ohms to 8 ohms, and about right for a suitable tube circuit if the Ra-a is about 90 ohms. 1/2 a 6080 Ra = 280 ohms, and a whole one has 140 ohms, a pair have 280 ohms a-a, and a six pack have Ra-a = 93 ohms, just what you want and you could get about 50 watts AB1 easily. They'l also go AB2, but maybe not much is gained except more thd, which isn't wanted. A 150Watt mains toroidal tranny could be fine, and is worth a try. Such mains trannies are dead useless for other large octal tubes, 6550 etc, because the AB load for a pair is typically 5k for 50 watts AB1 into 4 ohms, and 7k for 35 watts into 8 ohms, with most of the power class A. "Universal" mains toroidal trannies with two 120V primary windings are needed, and the secondary voltages of say 35V are a guide only, and could vary down to say 18V + 18V for a transistor amp PS. 240V : 18V gives 1.42k : 8 ohms. The 240V across the primary gives a Bmax of about 1.2Tesla at 50Hz. For good low bass you want 1.2T at say 20Hz, so the voltage across the primary should be no more than 240V / ( 50/20 ) = 100V only. 240Vrms into 1.42k = 40 watts only. For a guitar amp the mains toroidal is usable with 6080 but for hi-fi the available turns per volt are simply not high enough, no matter what the VA of the tranny is, because it will saturate at too high an F, especially when used with the high Z of bass speakers below 100Hz. Have fun, but I prefer the 6550, KT88, KT90, EL34, 6AC7, 2A3, 300B etc. Patrick Turner. |
#11
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
A lot of vintage 4k to 5k pp outputs have 16 and even 32 ohm taps.
Putting 8 ohms on the 16 or 32 ohm taps should get you into a better loading range for 6080's. A lot of PP 7591 output transformers have pretty low refected impedance, I believe. Bob H. |
#12
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
On Feb 18, 9:20 am, Patrick Turner wrote:
Patrick many thanks for the thoughtful reply. Some questions below... (snip) You can set up a PP pair of class AB1 6080 or aka 6AS7 with RL about 1k, a-a and Ea = 200V and if the Pda of the two tubes = 40W, then you get about 10Watts of clean power, or about 100Vrms a-a into the 1k, and gain at about 1.8, so you need about 30Vrms at the grid which is none more than for 6550 in triode. Do you mean two 6080 in mono P-P. i.e. two paralleled triodes per side, total 4 triodes each 1/2 a 6080, or just one 6080 in P-P (two 1/2 6080's)? I'm thinking about the latter, i.e. one mono PP amp with one 6080 (duplicated for stereo if it works.) 3k is to high, and the Vswing will be limited by the Ea, which cannot be much above 200V because the tube just doesn't like it, it tends to run away with current if the Ea is too high no matter what the applied grid bias voltage is. Pity, as I have the 3K option with the two 125E OPT's in the spares box. The peak Ia available is VERY high for a tube, and ppl have used a quad of 6080 for a basic OTL amp, and Atmasphere makes OTL with lots of 6AS7 as a commercial example. Not planning for OTL, not enough tubes, anyway. Its also possible to series connect the 6AS7 and use a cap coupled OPT which is a line voltage speaker tranny, Altronics of Western Aust make a toroidal one which I thought would work with the series PP. Might look into it... But a good use is the circlotron circuit with a low Z load on the primary. Two 200V floating supplies are needed. Starting to look contrived... using the 6080 is not worth that effort! Some toroidal mains transformers are OK to use because with say 240V : 2 x 35V windings you have 240 : 35 with both secs paralleled, giving TR = 6.86, ZR = 47:1 = 376 ohms to 8 ohms, and about right for a suitable tube circuit if the Ra-a is about 90 ohms. 1/2 a 6080 Ra = 280 ohms, and a whole one has 140 ohms, a pair have 280 ohms a-a, and a six pack have Ra-a = 93 ohms, just what you want and you could get about 50 watts AB1 easily. They'l also go AB2, but maybe not much is gained except more thd, which isn't wanted. A 150Watt mains toroidal tranny could be fine, and is worth a try. Such mains trannies are dead useless for other large octal tubes, 6550 etc, because the AB load for a pair is typically 5k for 50 watts AB1 into 4 ohms, and 7k for 35 watts into 8 ohms, with most of the power class A. "Universal" mains toroidal trannies with two 120V primary windings are needed, and the secondary voltages of say 35V are a guide only, and could vary down to say 18V + 18V for a transistor amp PS. 240V : 18V gives 1.42k : 8 ohms. The 240V across the primary gives a Bmax of about 1.2Tesla at 50Hz. For good low bass you want 1.2T at say 20Hz, so the voltage across the primary should be no more than 240V / ( 50/20 ) = 100V only. 240Vrms into 1.42k = 40 watts only. For a guitar amp the mains toroidal is usable with 6080 but for hi-fi the available turns per volt are simply not high enough, no matter what the VA of the tranny is, because it will saturate at too high an F, especially when used with the high Z of bass speakers below 100Hz. This is starting to look interesting... I just happen to have several salvaged mains transformers (from my company's dumpster - we used to build our own linear P/S's in the 1980's and have just chucked out the old parts.) They are PRI: 240, 220, 208, 133, 120, 0 VAC to SEC: 27.6 VAC CT, i.e. 13.8-0-13.8 VAC. Thhese have a CT 240 VAC PRI to 13.8 VAC SEC (using 1/2 of it.) For 8 an ohm speakers I make that about 2420 ohms plate-to-plate. Low enough for one 6080? These transformers are rated 63 VA, also 50-60 Hz. They have quite large iron cores but I don't know the design Bmax is. Your 20 Hz calculation (above) shows 100 VAC max across the "240" VAC primary for 1.2 Tesla (assumed), giving 5.75 VAC across the the 8 ohm speaker for only 4.13 watts. Not at all good! If we accept a roll off at modest 40 Hz we could allow 240/(50/40) = 192 VAC across the primary to get 11 volts across the 8 ohm speaker for just over 15 watts. A lot better, not at all bad for one O/P tube. So, I'll draw a few lines on the 6080 plate characteristics and see what gives. BTW, the tube rating goes to 250 VDC so might as well push it there. I would use cathode bias to keep it a bit safer, then, allowing for over 100 VDC of bias the B+ would be close to 350 VDC. In your opinion, is this worth a try? Cheers, Roger Have fun, but I prefer the 6550, KT88, KT90, EL34, 6AC7, 2A3, 300B etc. Patrick Turner.- Hide quoted text - - Show quoted text - |
#13
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Hi RATs!
Yes! I have a buch of various 6AS7G and 6080. I grabbed them from clearance sales from Auntie Klektronic Sply over the years. I am looking forward to them finding a cure for my CFS, so I can try them out. Meanwhile, I just swap caps and go ooh! ooh! baby! baby! baby! I turned 60 last Friday, so, there is still time ... Happy Ears! Al |
#14
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
"Bob H." wrote: A lot of vintage 4k to 5k pp outputs have 16 and even 32 ohm taps. Putting 8 ohms on the 16 or 32 ohm taps should get you into a better loading range for 6080's. A lot of PP 7591 output transformers have pretty low refected impedance, I believe. Bob H. This is a solution which could be tried. However, there is a downside. A typical old OPT with ratio of 5k:15 will have 10% winding losses, ie looking into the primary, the total winding resistance will be 500 ohms of the primary dcr wire resistance and the reflected secondary winding resistance. So when you have 8 ohms connected to a 16 ohm tap, or to a 16 ohm winding which was most common in 1955, then the primary load is 2k5, but the winding resistance remains at 500 ohms so losses rise to 20%. When 4 ohms is connected to the 16 ohm winding, losses = 40%. The main problem with the 6080/6AS7 tube used for an amp is that once it is built, there isn't any other tube that will suit the PS and OPT easily. With an amp designed for EL34, one can usually fiddle with the circuit to make it suit 6L6, KT66, KT88, KT90, 6V6, 6CM5, 6DQ6 etc, etc. Patrick Turner |
#15
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
Engineer wrote: On Feb 18, 9:20 am, Patrick Turner wrote: Patrick many thanks for the thoughtful reply. Some questions below... (snip) You can set up a PP pair of class AB1 6080 or aka 6AS7 with RL about 1k, a-a and Ea = 200V and if the Pda of the two tubes = 40W, then you get about 10Watts of clean power, or about 100Vrms a-a into the 1k, and gain at about 1.8, so you need about 30Vrms at the grid which is none more than for 6550 in triode. Do you mean two 6080 in mono P-P. i.e. two paralleled triodes per side, total 4 triodes each 1/2 a 6080, or just one 6080 in P-P (two 1/2 6080's)? I'm thinking about the latter, i.e. one mono PP amp with one 6080 (duplicated for stereo if it works.) 3k is to high, and the Vswing will be limited by the Ea, which cannot be much above 200V because the tube just doesn't like it, it tends to run away with current if the Ea is too high no matter what the applied grid bias voltage is. Pity, as I have the 3K option with the two 125E OPT's in the spares box. Before leaping into a project, I always work out the load lines for myself. Other wise I am guessing what might work, or might not, and what I have said here about 6080 is little more than guesswork because I have not done the graphical analysis to get a projected outcome which could be within 10% of being accurate. There is a lot you could learn about such analysis from the old books, or at the many good websites around, perhaps even including my own, http://www.turneraudio.com.au But I can say a 3k anode to anode load will NOT hurt a pair of 6080 if you connect such a load. Perhaps you'll wonder why there is so little power, but one needs to consider basic triode class A1 efficiency which won't ever be more than about 30%, if RL is made a lot larger than Ra, which means you must have a high as possible Ea, and as low as possible Ia which still gives about 80% of the rated data maximum Pda for the triode, and so if you have 40watts of Pda from two tubes with two triodes within each, 10W each, then 12 watts is the class A outer limit of power. But its very NICE power, because it will have low thd/imd, and the Rout of the amp measured at the sec will be very low. 12 watts into 3k means you must have 190Vrms anode to anode, which is 95Vrms of opposite phased signal at each anode, and a mains transformer which can take 240V across its centre tapped primary would be OK, although saturation would be at about 40Hz at 1.2Tesla. 48 watts into 3k is 380Vrms a-a, and the OPT would saturate at 80Hz if it was a mains tranny, so its NO GOOD. But if you reduced the a-a RL from 3k to 1k, and still have your 190Vrms a-a but using 6 x 6080, then you'd get 36 watts, and saturation would still be at 40Hz, assuming it was the same OPT but with a lower sec load to reduce the primary load, and with the same turns per volt. Because you'd have a much higher and useful power ceiling with 6 tubes, you can afford to back the bias off to allow class AB1, and more relaxed tube temperatures and longer life, and there would be 9 watts available at only 1/2 the output voltage level, so the saturation F would fall to 20Hz. Every way you look at it, more tubes = a better amp. The peak Ia available is VERY high for a tube, and ppl have used a quad of 6080 for a basic OTL amp, and Atmasphere makes OTL with lots of 6AS7 as a commercial example. Not planning for OTL, not enough tubes, anyway. Its also possible to series connect the 6AS7 and use a cap coupled OPT which is a line voltage speaker tranny, Altronics of Western Aust make a toroidal one which I thought would work with the series PP. Might look into it... But a good use is the circlotron circuit with a low Z load on the primary. Two 200V floating supplies are needed. Starting to look contrived... using the 6080 is not worth that effort! Nah, the circlotron only takes two B+ supplies, not just one for a channel, and its not all that difficult at all. There are benefits in that the OPT does not have to be centre tapped and the "anode to anode" load is 1/4 of conventional a-a load used in class A amps. The conventional layout is all one needs though, and the circlowhizzy IS slightly more difficult for the diyer who must spend more on PTs, diodes and supply caps. Some toroidal mains transformers are OK to use because with say 240V : 2 x 35V windings you have 240 : 35 with both secs paralleled, giving TR = 6.86, ZR = 47:1 = 376 ohms to 8 ohms, and about right for a suitable tube circuit if the Ra-a is about 90 ohms. 1/2 a 6080 Ra = 280 ohms, and a whole one has 140 ohms, a pair have 280 ohms a-a, and a six pack have Ra-a = 93 ohms, just what you want and you could get about 50 watts AB1 easily. They'l also go AB2, but maybe not much is gained except more thd, which isn't wanted. A 150Watt mains toroidal tranny could be fine, and is worth a try. Such mains trannies are dead useless for other large octal tubes, 6550 etc, because the AB load for a pair is typically 5k for 50 watts AB1 into 4 ohms, and 7k for 35 watts into 8 ohms, with most of the power class A. "Universal" mains toroidal trannies with two 120V primary windings are needed, and the secondary voltages of say 35V are a guide only, and could vary down to say 18V + 18V for a transistor amp PS. 240V : 18V gives 1.42k : 8 ohms. The 240V across the primary gives a Bmax of about 1.2Tesla at 50Hz. For good low bass you want 1.2T at say 20Hz, so the voltage across the primary should be no more than 240V / ( 50/20 ) = 100V only. 240Vrms into 1.42k = 40 watts only. For a guitar amp the mains toroidal is usable with 6080 but for hi-fi the available turns per volt are simply not high enough, no matter what the VA of the tranny is, because it will saturate at too high an F, especially when used with the high Z of bass speakers below 100Hz. This is starting to look interesting... I just happen to have several salvaged mains transformers (from my company's dumpster - we used to build our own linear P/S's in the 1980's and have just chucked out the old parts.) But what sort of mains trannies are they? If they are toroidal types, perhaps you are in luck since they will have a good HF response maybe. But if they are E&I bobbin type trannies, perhaps you may find the HF response quite dismal, maybe you get 5kHz, and this is if they have concentric windings. If the windings are side by side with a plastic divider between each side for the P and S group of windings, HF performance will be even worse, and nothing can fix this. They are PRI: 240, 220, 208, 133, 120, 0 VAC This gives what looks to be a 240V winding with CT. But probably, the 240V winding has two wire sizes, for 0-133, its thick wire, then maybe from 133 its much thinner wire because I in with 240V P is 1/2 the I in with 120V, and this means you have assymetrical P 1/2 windings. It won't matter much and will still work, but other serious assymetries may exist such as very different and large amounts of leakage inductance and shunt capacitance. If you are building a guitar amp, or modulator for an amateur radio station, the HF roll off just above 3khz that you are likely to find may not matter one bit. to SEC: 27.6 VAC CT, i.e. 13.8-0-13.8 VAC. Thhese have a CT 240 VAC PRI to 13.8 VAC SEC (using 1/2 of it.) For 8 an ohm speakers I make that about 2420 ohms plate-to-plate. Low enough for one 6080? Theoretically its OK for a pair of tubes, ie two tubes with the two triodes within each paralleled. Even ONE x 6080 would work, but power would be very low unless you begin to work well into class AB. transformers are rated 63 VA, also 50-60 Hz. They have quite large iron cores but I don't know the design Bmax is. As long as the mains tranny VA is about twice the intended maximum audio power output is, there is no worry about power handling; the limitations are saturation at LF and HF response. Your 20 Hz calculation (above) shows 100 VAC max across the "240" VAC primary for 1.2 Tesla (assumed), giving 5.75 VAC across the the 8 ohm speaker for only 4.13 watts. Not at all good! Well nearly all commercially designed mains trannies are designed to have a magnetic field strength maximum of between 0.8Tesla for hi-fi amp PTs, to 1.3T in hot running industrial PTs. The less turns per volt, the hotter the core runs and the greater the distortions, and the nearer you are to complete saturation. In good trannies with GOSS cores, and many don't have such a good grade of iron, the turns used produce 1.2T and 3% THD, but if you tried to run the 240V at 25Hz instead of 50Hz, the core would seriously overheat and distortion might be 60%, and a disater is immiment. But you could run the 240V tranny at 120Vrms at 25Hz OK, and the Bmax is 1.2T. With an amp, it will rarely need to have the ability to make a full 240V at any F and so having the 20Hz saturation at 100Vrms, 1.2T, is OK for non critical audio. For real hi-fi, all such proposed use of mains trannies is complete BS, because we'd want to get full power down to 13Hz perhaps, so this means very many more turns per volt wound on the core; the whole design is far more complex and must provide also for the interleaving needed for a decent HF. Hammond quality is where one starts when doing diy, but for serious hi-fi one has to go to Plitron, Lundahll, Sowter, or some other respected brand, or else gird the loins and build a lathe, and learn all about it and wind your own OPT. The latter option is where i went, and its all explained at my website. The Hammond option isn't expensive in the US, where freight costs are confined but here in Oz the freight is a major component. Its better to spend on a Hammond for say US $100 than put a badly matched mains tranny worth $50 in they amp, IMHO. If we accept a roll off at modest 40 Hz we could allow 240/(50/40) = 192 VAC across the primary to get 11 volts across the 8 ohm speaker for just over 15 watts. A lot better, not at all bad for one O/P tube. So, I'll draw a few lines on the 6080 plate characteristics and see what gives. BTW, the tube rating goes to 250 VDC so might as well push it there. Don't push your luck with 6080 too far by going to the rated maxVdc Ea for the tube. You may not have to and maybe you'd still get the wanted anode V swing and power. I would use cathode bias to keep it a bit safer, then, allowing for over 100 VDC of bias the B+ would be close to 350 VDC. In your opinion, is this worth a try? Cheers, Roger All teaching exercizes are worth a try, smoke generation in the work shed is always a questionable goal :-) Without any load on the amp and with just the primary winding, at 1khz the primary load is very high at about 1,000 x 6.28 x inductance at 1kHz. Now the primary L at 1khz isn't the same as it is at its maximum at about 20Hz, depending on the irn type, and the applied voltage, and often the 1khz L is 1/20 of the value at 20Hz, but nevertheless the 1kHz load with no secondary load is well above the intended R load in ohms, and the fact it is purely inductive won't matter because the Ra-a of the tubes will be a far lower ohm value than the ZL, the reactance in ohms of the LP at 1kHz. But at 1kHz is where you should first get the amp to work, and use a sine wave. Use square waves only when you have things going right with a sine wave If you have cathode bias, use separate RC networks for each cathode. Start loading the amp with 64 ohms and work downwards to 2 ohms in steps of 64, 32, 24, 16, 12, 8, 6, 5, 4, 3, 2. Record the output voltage at clipping into each load, and draw a graph of the power vs load curve. It will be an arch. Record where the cathode Ek rises more than 10%; this is where the class A operation ceases, and class AB is deemed to have begun. With 2 ohms, the Ek may double. The peak in the arch should be at loads under 4 ohms and at about 3 ohms. If you are happy with the power levels into 4 ohms without more than 30% of Ek rise, then the amp is loaded about right, and will still provide useful power into all loads between 3 and 16 ohms, and most speakers lie within this range. Some may say it doesn't matter about the Ek rise with class AB, and AB2 op would be fine, but then thd/imd leaps to large numbers. Extracting huge audio power from a minimum of glassware involves higher tolerance for poor technical excellence in performance. Perhaps its OK, even desirable if you have a guitar amp where the more distortion the merrier, but not for hi-fi. The 6080 can produce huge peak currents ( for a tube ), for short period signal swings, hence their ability in OTL amps. The same current ability exists in transformer coupled output stages but is rarely used, unless the load is reduced to 1 ohm, but then the OPT behaves like a resistance of low value because the winding resistance is like a fixed value of R in series with the input to the primary if considered a perfect tranny with no winding resistance. So with a 1 ohm load, most of the power goes to heat the winding wire rather than give much output power. Don't prolong tests with 1 ohm. Such tests of 20 seconds won't hurt at clipping, but Pda will be perhaps over the rating and tubes can turn red and DIE BY MELTDOWN if left running into too low a load for too long; and you don't need to have a high level of output volume to cause the meltdown, and its how many amps are killed by their owners; they neglect and/or don't notice when one channel has a shorted speaker lead, or partially shorted speaker. More critical choices for loading can be done using varied arrangements of secondary windings on the OPT but if you have a mains tranny to begin with you probably won't have the luxury of such an option that would be correct. two 13.8V windings in parallel might match give 2 ohms, but in series they match 8 ohms, and this lack the flexibilty of also having a 4 ohm match, so all speakers between 1 ohm and 4 ohms use the 2 ohm outlet, and all speakers 4 ohms and above use the 8 ohm outlet. vey few speakers need to be connected to 2 ohms, because their average Z hovers arong 5 ohms these days. The slow drift to low Z speakers over the last 50 years is due to the emergence of SS amps which can cope quite OK with one ohm loads if there are enough output transistors and you don't need a high rail voltage for huge powers. Patrick Turner. Have fun, but I prefer the 6550, KT88, KT90, EL34, 6AC7, 2A3, 300B etc. Patrick Turner.- Hide quoted text - - Show quoted text - |
#16
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
tubegarden wrote: Hi RATs! Yes! I have a buch of various 6AS7G and 6080. I grabbed them from clearance sales from Auntie Klektronic Sply over the years. I am looking forward to them finding a cure for my CFS, so I can try them out. Meanwhile, I just swap caps and go ooh! ooh! baby! baby! baby! I turned 60 last Friday, so, there is still time ... Happy Ears! Al I stole Aunty Kleptomniac's last tubes. Got her back at last. Hmm, ohhh AAAAhh, wooooahhh..... Patrick Turner. |
#17
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
On Feb 19, 12:22 am, Patrick Turner wrote:
"Bob H." wrote: A lot of vintage 4k to 5k pp outputs have 16 and even 32 ohm taps. Putting 8 ohms on the 16 or 32 ohm taps should get you into a better loading range for 6080's. A lot of PP 7591 output transformers have pretty low refected impedance, I believe. Bob H. This is a solution which could be tried. However, there is a downside. A typical old OPT with ratio of 5k:15 will have 10% winding losses, ie looking into the primary, the total winding resistance will be 500 ohms of the primary dcr wire resistance and the reflected secondary winding resistance. So when you have 8 ohms connected to a 16 ohm tap, or to a 16 ohm winding which was most common in 1955, then the primary load is 2k5, but the winding resistance remains at 500 ohms so losses rise to 20%. When 4 ohms is connected to the 16 ohm winding, losses = 40%. The main problem with the 6080/6AS7 tube used for an amp is that once it is built, there isn't any other tube that will suit the PS and OPT easily. With an amp designed for EL34, one can usually fiddle with the circuit to make it suit 6L6, KT66, KT88, KT90, 6V6, 6CM5, 6DQ6 etc, etc. Patrick Turner I'm used to more like 200 to 300 ohm resistance in 7591 primary windings, and a Heathkit mono 7591 amp on my bench right now shows 220 ohms plate to plate on the output tranny. I'm sure the reflected load is around 4 to 5k, so the 16 ohm tap would yield around 2 to 2.5 k impendance. Bob H. |
#18
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
"Bob H." wrote: On Feb 19, 12:22 am, Patrick Turner wrote: "Bob H." wrote: A lot of vintage 4k to 5k pp outputs have 16 and even 32 ohm taps. Putting 8 ohms on the 16 or 32 ohm taps should get you into a better loading range for 6080's. A lot of PP 7591 output transformers have pretty low refected impedance, I believe. Bob H. This is a solution which could be tried. However, there is a downside. A typical old OPT with ratio of 5k:15 will have 10% winding losses, ie looking into the primary, the total winding resistance will be 500 ohms of the primary dcr wire resistance and the reflected secondary winding resistance. So when you have 8 ohms connected to a 16 ohm tap, or to a 16 ohm winding which was most common in 1955, then the primary load is 2k5, but the winding resistance remains at 500 ohms so losses rise to 20%. When 4 ohms is connected to the 16 ohm winding, losses = 40%. The main problem with the 6080/6AS7 tube used for an amp is that once it is built, there isn't any other tube that will suit the PS and OPT easily. With an amp designed for EL34, one can usually fiddle with the circuit to make it suit 6L6, KT66, KT88, KT90, 6V6, 6CM5, 6DQ6 etc, etc. Patrick Turner I'm used to more like 200 to 300 ohm resistance in 7591 primary windings, and a Heathkit mono 7591 amp on my bench right now shows 220 ohms plate to plate on the output tranny. This is about the usual fare, and if the P losses are 10%, primary RL = 2k2. If 5%, RL a-a = 4k4. I'm sure the reflected load is around 4 to 5k, so the 16 ohm tap would yield around 2 to 2.5 k impendance. Total Rw with secondary usually total around 10% in average quality OPT, 5% or less for real good ones, and up to 25% Rw losses ( copper losses ) for a crummy mantle radio, and usually the secondary has more Rw than the P, perhaps because most makers think there is more danger of a P winding fusing with too much DC, and they are right. Small average amounts of music will never fuse a secondary winding on an OPT. So they use thn wire to help pay for their BMW. With a Z ratio of 4k:8, the ZR = 500:1. If the winding R of the sec = 1 ohm, then at the P this appears as 500 ohms. So if the P = 220ohms, total Rw lokking into the P = 220 + 500 = 720 ohms. S dcr can only be checked with something that reads low dcr accurately, and you need to know the unloaded voltage ratio at 400Hz for the TR, which squared gives the ZR, and you then have the voltage ratio for a perfect tranny, andthe dcr of P and S can be added to it to draw up the model of what you have in an amp. Clever dicks measure the OPT with 400Hz, or 1kHz, something around these F, and with 1kohm in series with the P, and a low Z out voltage gene capable of say 50Vrms to simulate a tube in the output. Such folk don't need to make dc resistance measurements, they make these parameters clear by careful routine ac signal measurements and by later calculation because the clever dick has the mental picture of the tranny model firmly in his head. The leakage inductance and shunt C can also be checked out during the process... Patrick Turner. Bob H. |
#19
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
"Ernst" writes:
Roger, The 6080 (and it's close kin, the 6082) have a claim to fame in the audio world: OTL! (Output TransformerLess). There is an excellent example of this in Terman's "Radio Engineer's Handbook", Mcgraw-Hill, 1954. The idea is to take advantage of the low plate resistance exhibited by this tube, and stack several in series-parallel to directly drive a loudspeaker. Best regards, Ernst Only has an amplification factor of 2. You can do nicely with other tubes as cathode followers. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#20
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
On Feb 20, 6:42 pm, (Steven Swift) wrote:
"Ernst" writes: Roger, The 6080 (and it's close kin, the 6082) have a claim to fame in the audio world: OTL! (Output TransformerLess). There is an excellent example of this in Terman's "Radio Engineer's Handbook", Mcgraw-Hill, 1954. The idea is to take advantage of the low plate resistance exhibited by this tube, and stack several in series-parallel to directly drive a loudspeaker. Best regards, Ernst Only has an amplification factor of 2. You can do nicely with other tubes as cathode followers. -- Steven D. Swift, ,http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA True, but... http://www.1212designs.com/OTL_Stereo_Amp/default.htm |
#21
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
"Ernst" writes:
Only has an amplification factor of 2. You can do nicely with other tubes as cathode followers. -- True, but... http://www.1212designs.com/OTL_Stereo_Amp/default.htm That's an impressive number of 6080's. It will keep you warm. -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
#22
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
RCA had a decent sounding amp in their manual. It has
6sn7 line stage with 6sn7 splitter and one 6as7. I have bult a 6as7 p-p, otl and headphone amp. and it makes a great preamp regulator. I use them when I make studio gear. Sal Brisindi wrote: Engineer wrote: Hi, Vacuumlanders. Just a speculation but has anyone built a P-P audio ampliifier with the 6080 (6AS7) tube? (twin power triodes used as the series element in voltage regulators) OK, why would you want to?... it's low voltage, high current, high bias, likely difficult to drive, you don't need to since there are plenty of better alternatives, etc... My answer: I have several 6080's (mostly NOS); getting bored with designing for 6V6, 6L6, EL84, EL34, etc (well, not really!); you get P- P in one envelope; I have a couple of spare universal replacement OPT's (the Hammond 125E) so a choice of plate-to-plate impedances from 3000 ohm up (low enough?) is easily obtained; two O/P tubes for stereo; and, finally, the 6080 sort of looks nice! So, any opinions on this?... including don't bother! g Cheers, Roger I bought a couple of 6AS7's but did not yet build an amp with them. I think it would be cool to have a push-pull tube amp in one envelope. Regards, Sal |
#23
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
On Feb 24, 3:04 pm, "John" wrote:
RCA had a decent sounding amp in their manual. It has 6sn7 line stage with 6sn7 splitter and one 6as7. I have bult a 6as7 p-p, otl and headphone amp. and it makes a great preamp regulator. I use them when I make studio gear. I'll take a look... missed that one! Anyway, back to the power transformer recycling notion mentioned earlier... I drew some load lines on the 6080 plate chcs to no great profit, except to show over 100 VDC bias in the 250 volt and 30 mA operating region. So, I ran up a breadboard trial today with a 6080 feeding the primary a 240 VAC CT MT (CT to B+, plates to either end) with a 13.8 VAC secondary to 8 ohm load resistor, a "MT/OPT". Resulting p to p impedance: 2420 ohms (see above.) I used a 1.8 kohm WW resistor (as it was to hand, close enough) as a common cathode bias. How to drive it? I did not feel like building a 6SN7 phase splitter, nor taking a feed from another PP amplifier with the OPT tubes removed (too many B+ issues), so I just used a backwards connected PP OPT (the Hammond 125E) as a driver transformer and fed it from the speaker output of a another amplifier. B+ and heater was from a Heathkit bench supply. Sig. gen. to driver amp, of course. First the operating points - no drive B+ I(total, 2 sections) V cathode bias 150 30 mA 52.6 200 40 69.8 250 50 87.1 300 60 105.3 The last point started to look promising, but read on... Then, at 300 VDC, I tried to drive it. BTW, the speaker level drive to the 125E "OPT" remained undistorted (as checked on 'scope) over the whole experiment. I started at 400 Hz. Very bad results! The maximum visibly undistorted voltage I could get across the 8 ohms load on the "MT/OPT" secondary was 2 VAC, for an O/P power of 0.5 watts. This was sustained from about 40 Hz to 5KHz. I then added bias from some batteries between "MT/OPT" CT and ground to get it a bit more into class AB. I took the bias up to 128 VDC (fixed plus cathode R drop.) Quiescent total current dropped to 43 mA but no more power achieved. Tried 4 ohm load... worse. Max volts 0.6 VAC for less than 1/10 of a watt. Stopped for coffee and contemplation... and to send this in. I might be worth trying the 125E OPT properly, but I must admit that I am losing any affection I ever had for the 6080 outside of use as a series power regulator- it sits there like a miniature two-bar electric fire laughing at you as it delivers half a watt! g Of course, not fair to judge it with a "MT/OPT" kludge! If I get any further I'll post results. Cheers, Roger |
#24
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
I used a hammond 1645 output transformer (30w 5000ohm plate to plate) my B+ around 320
VDC. I built mine like the 1956 RCA manual (page 276) with a few execptions: my power transformer was a 240AC full wave bridge rectified by 6A10. I used two 193d inductors (hammond 8H@150mA )and four 33uf 630v poly caps (solen) and .1 uf on the end of the power supply. I use a 5vdc industral switcher tweaked to 6Vdc for the heaters. I split chasis my amp the power supply is on one chassis and the amp on another. This lets me tweak the power supply separately from the amp and it helps with controlling the magnetic noise the power supply emits . I use jones connectors for my power interconnects. In most of the tube push pull amp the output stage acts really like a buffer, the voltage gain is happening before it in the tube predriver stage before the pase split . In the 6as7's case, needs a really high impedence input with about 60-80% of what signal you want the output comming out of it. and the grid loading the 6as7 reflected back to the phase splitter should be isolated by some type of balanced driver stage. And last, it needs the medium-low impedence load of 2500 ohms per plate to establish the idle current without causing transformer saturation. I go about 2-3 times over on power rating of the output transformer to the circuit to achieve low transformer saturation and better bandwidth. its about 12 watts of amp. I was going to expirament with using a signal transformer 600:50k ct (sowter 9062) grounded center tap sec. and two stages of john brooskie's akido per signal path (one two tube 6sn7 for the signal + and one two tube 6sn7 for signal - ) as a balanced amp. Otherwise, to cut parts count down, a simple 6sn7 or 6sl7 common cathode will fit the bill. If you dont have any of those octals try 12ax7, 12ay7, 12au7 9 pins. this is the link to RCA amp above: http://www.kbapps.com/audio/tubemanual/276.html "Engineer" wrote: On Feb 24, 3:04 pm, "John" wrote: RCA had a decent sounding amp in their manual. It has 6sn7 line stage with 6sn7 splitter and one 6as7. I have bult a 6as7 p-p, otl and headphone amp. and it makes a great preamp regulator. I use them when I make studio gear. I'll take a look... missed that one! Anyway, back to the power transformer recycling notion mentioned earlier... I drew some load lines on the 6080 plate chcs to no great profit, except to show over 100 VDC bias in the 250 volt and 30 mA operating region. So, I ran up a breadboard trial today with a 6080 feeding the primary a 240 VAC CT MT (CT to B+, plates to either end) with a 13.8 VAC secondary to 8 ohm load resistor, a "MT/OPT". Resulting p to p impedance: 2420 ohms (see above.) I used a 1.8 kohm WW resistor (as it was to hand, close enough) as a common cathode bias. How to drive it? I did not feel like building a 6SN7 phase splitter, nor taking a feed from another PP amplifier with the OPT tubes removed (too many B+ issues), so I just used a backwards connected PP OPT (the Hammond 125E) as a driver transformer and fed it from the speaker output of a another amplifier. B+ and heater was from a Heathkit bench supply. Sig. gen. to driver amp, of course. First the operating points - no drive B+ I(total, 2 sections) V cathode bias 150 30 mA 52.6 200 40 69.8 250 50 87.1 300 60 105.3 The last point started to look promising, but read on... Then, at 300 VDC, I tried to drive it. BTW, the speaker level drive to the 125E "OPT" remained undistorted (as checked on 'scope) over the whole experiment. I started at 400 Hz. Very bad results! The maximum visibly undistorted voltage I could get across the 8 ohms load on the "MT/OPT" secondary was 2 VAC, for an O/P power of 0.5 watts. This was sustained from about 40 Hz to 5KHz. I then added bias from some batteries between "MT/OPT" CT and ground to get it a bit more into class AB. I took the bias up to 128 VDC (fixed plus cathode R drop.) Quiescent total current dropped to 43 mA but no more power achieved. Tried 4 ohm load... worse. Max volts 0.6 VAC for less than 1/10 of a watt. Stopped for coffee and contemplation... and to send this in. I might be worth trying the 125E OPT properly, but I must admit that I am losing any affection I ever had for the 6080 outside of use as a series power regulator- it sits there like a miniature two-bar electric fire laughing at you as it delivers half a watt! g Of course, not fair to judge it with a "MT/OPT" kludge! If I get any further I'll post results. Cheers, Roger |
#25
Posted to rec.audio.tubes
|
|||
|
|||
6080 audio amp?
John wrote in message news:BJ6dnX5CzPSozH7YnZ2dnUVZ_tSunZ2d@prairiewave. com... I used a hammond 1645 output transformer (30w 5000ohm plate to plate) my B+ around 320 VDC. I built mine like the 1956 RCA manual (page 276) with a few execptions: my power transformer was a 240AC full wave bridge rectified by 6A10. I used two 193d inductors (hammond 8H@150mA )and four 33uf 630v poly caps (solen) and .1 uf on the end of the power supply. I use a 5vdc industral switcher tweaked to 6Vdc for the heaters. I split chasis my amp the power supply is on one chassis and the amp on another. This lets me tweak the power supply separately from the amp and it helps with controlling the magnetic noise the power supply emits . I use jones connectors for my power interconnects. In most of the tube push pull amp the output stage acts really like a buffer, the voltage gain is happening before it in the tube predriver stage before the pase split . In the 6as7's case, needs a really high impedence input with about 60-80% of what signal you want the output comming out of it. and the grid loading the 6as7 reflected back to the phase splitter should be isolated by some type of balanced driver stage. And last, it needs the medium-low impedence load of 2500 ohms per plate to establish the idle current without causing transformer saturation. I go about 2-3 times over on power rating of the output transformer to the circuit to achieve low transformer saturation and better bandwidth. its about 12 watts of amp. I was going to expirament with using a signal transformer 600:50k ct (sowter 9062) grounded center tap sec. and two stages of john brooskie's akido per signal path (one two tube 6sn7 for the signal + and one two tube 6sn7 for signal - ) as a balanced amp. Otherwise, to cut parts count down, a simple 6sn7 or 6sl7 common cathode will fit the bill. If you dont have any of those octals try 12ax7, 12ay7, 12au7 9 pins. this is the link to RCA amp above: http://www.kbapps.com/audio/tubemanual/276.html How do you like the sound of this amp??? I think it would be a good candidate for a CT choke loaded driver to get low distortion AF voltage swing at the 6AS7 grids. you might look into John Stewarts "Bootstrap" 6AS7 amp.....There are alot of these regulator tubes to be had at cheap prices...GC |
#26
|
|||
|
|||
Quote:
If anyone would like to have copies of the original circuits, pls ask. cheers, John |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
It's amazing what you can find when you look. | Audio Opinions | |||
Artists cut out the record biz | Pro Audio |