I have some nice transmitter tubes (two brand new qbl3/3500 tetrodes etc.) and I was thinking if it is possible to use these as hige audio hi-fi amplifier?
Class A - lots of heat! But not too hard to built..No need for center tapped output transformer.
Class AB - Enough output power. Much better efficiency. Needs huge center tapped output xfrmr..
What comes to powersupply, I have xfrmrs like 2kV/0.1A....pair of 6kV/1A pigs. So that is not a problem.
Filament supply - Seems to be difficult as those tubes requires 6V/32A each..And it should be well filtered DC? big rectifier diodes and huge capacitor bank. Propably switching mode psu will do the job.
Anyway, I was considering to use my 2x100W amplifier for driving these tubes via coupling transformer. So there is no other tube stages, only power stage.
Any good ideas for this kind of amplifier? I know lots of people using RF power amp tubes as hifi amplifier finals but those are using much smaller power tubes.
Class A - lots of heat! But not too hard to built..No need for center tapped output transformer.
Class AB - Enough output power. Much better efficiency. Needs huge center tapped output xfrmr..
What comes to powersupply, I have xfrmrs like 2kV/0.1A....pair of 6kV/1A pigs. So that is not a problem.
Filament supply - Seems to be difficult as those tubes requires 6V/32A each..And it should be well filtered DC? big rectifier diodes and huge capacitor bank. Propably switching mode psu will do the job.
Anyway, I was considering to use my 2x100W amplifier for driving these tubes via coupling transformer. So there is no other tube stages, only power stage.
Any good ideas for this kind of amplifier? I know lots of people using RF power amp tubes as hifi amplifier finals but those are using much smaller power tubes.
Before going any further, let's clear up something. When you say class A has "No need for center tapped output transformer," you must be referring to single-ended operation. Indeed, there is no need for a center tap, but... there IS a need for a gapped core, and that means that for a given power, that transformer will need to be much bigger and more expensive than the equivalent center-tapped transformer for push-pull (regardless of class of operation).
Well, that was only grazy idea so I know that there is much to learn about. I have made many smaller tubeamps like 1..100W output/4x EL34 but this is a way different.
So, I need gapped core output transformer..hmm, I have no idea. Why is that? I haven't seen before airgapped output transformers..
So, I need gapped core output transformer..hmm, I have no idea. Why is that? I haven't seen before airgapped output transformers..
There are some work-arounds to the gapping requirement, but they carry their own baggage.
In any case, to supply the plate, DC must flow through the transformer. The magnetic field from the DC will take the core toward saturation. In a push-pull design, the DC-induced field is canceled out by the current in the two haves flowing in the opposite direction. This is not the case for SE, so the gapped core is generally used.
In any case, to supply the plate, DC must flow through the transformer. The magnetic field from the DC will take the core toward saturation. In a push-pull design, the DC-induced field is canceled out by the current in the two haves flowing in the opposite direction. This is not the case for SE, so the gapped core is generally used.
SY,
We'll go parafeed...
But, I'd not play around with extreme high voltage unless you have significant experience with it.
HIGH VOLTAGE AT MODEST CURRENTS IS INSTANTLY DEADLY!!
HIGH VOLTAGE AT MODEST CURRENTS IS INSTANTLY DEADLY!!
And then there is the question of where you'd get an output xfmr with a high enough primary Z that has any freq response worth a damn, and a size that is comensurate??
There's probably a reason that this isn't done much...
I'd take a really hard look at plate curves, (assuming a pentode - strapped into triode), with reduced plate voltage and run in class A, and see how low you can go with the B+ and how low you can get the output Z to fall... then you have half a shot, imho...
_-_-bear
We'll go parafeed...
But, I'd not play around with extreme high voltage unless you have significant experience with it.
HIGH VOLTAGE AT MODEST CURRENTS IS INSTANTLY DEADLY!!
HIGH VOLTAGE AT MODEST CURRENTS IS INSTANTLY DEADLY!!
And then there is the question of where you'd get an output xfmr with a high enough primary Z that has any freq response worth a damn, and a size that is comensurate??
There's probably a reason that this isn't done much...
I'd take a really hard look at plate curves, (assuming a pentode - strapped into triode), with reduced plate voltage and run in class A, and see how low you can go with the B+ and how low you can get the output Z to fall... then you have half a shot, imho...
_-_-bear
tonskulus said:
Sure, anything's possible, but that's not really the question. Have you checked the specs on that? Why would you ever need 7200W of audio power? Let's not forget that, at the stated efficiency of 65%, you will be needing at least 11KW of DC input power, and that's not accounting for efficiency losses on the AC side.
Are you planning on having your power company install your own, personal, three phase substation? Because you're sure gonna need one.
I'd say FUGGEDABOUDIT, sell those to the VHF contest fanatics with a burning desire to win contests, way too much time and money on their hands, and no conscience, who already build illegal VHF rigs for winning contests that provide nothing more than braggin' rights.
You could use the proceeds to build a few really decent -- and practical -- HiFi rigs.
bear said:
That won't work either. The Vsgsg max is 800V. It's a true tetrode, not a pentode or beam tube either. For any Vpk below 1000V, the plate curves kink badly. 800V would put that right in the middle of a neagtive resistance characteristic that's far from linear, and would result in uncontrollable instability.
No such fun, my wife's stepfather is in the "end stages" of a rare terminal bone marrow disease. Things have been rather hectic lately. I have 2 amplifiers on my bench now that have been there for about 3 months. On a more positive note, today was a holiday from work, and I am about to flip the switch on one of them for the first time. I had to get away from it for a few minutes before I give it a final check over.
Yes, I am an RF engineer, but in my world BIG power is 100 watts and most of my designs are under 10 watts, ALL solid state. I built some tube RF amplifiers for ham use at power levels up to 2 KW, but that was years ago. I have a bunch of transmitter tubes, and have experimented with some of them. I have found that the biggest problem in building "the big one" is finding a suitable output transformer.
As mentioned before, In a conventional single ended design the tube current flows through the output transformer. The short story is that the transformer must be large. A 25 watt transformer weighs about 10 pounds, a 50 watt transformer weighs about 25 pounds. See this thread for more details:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=94047
As stated before the efficiency of a single ended design runs from 5 to 20%. The other 80 to 95% will be heating your whole house.
A push pull design would be far more efficient, and the transformer would be smaller since the opposing currents cancel the magnetic field. It would be possible to have a custom transformer built for these applications, but it will cost a small fortune at the power levels that these tubes could produce.
If you didn't need to cover the entire audio bandwidth, the transformer issue becomes a little easier. In my younger years I used a HV power transformer hooked up backwards as a push pull output transformer. It sucked as a HiFi transformer, but made an awesome guitar amp. A whole lot of experimentation is required here to find a suitable transformer.
I am of the opinion that a big transmitting tube amp would be easiest to build with a low Mu or medium Mu triode since the plate resistance is lower easing the transformer requirements. A triode wired pentode would be OK if the maximum screen grid voltage is high enough.
As mentioned before, the voltages required to run tubes like these are INSTANTLY LETHAL if contacted! You do not get a second chance. DO NOT GO HERE unless you have a lot of experience with HV and tube designs.
As also mentioned before, the practicality (and reliability) of such an amplifier is questionable at the very least. You better live where it is real cold, and park it for the entire summer! I have a 40 WPC SE amplifier that uses 845 transmitting tubes. It pumps about 300 watts worth of heat into the room. I have added a small window AC to supplement the central AC in my lab, and I still don't use that amp much because of the heat. When I was thinking about the 833A SE design, I had planned to use a vent system from a clothes dryer to get the heat out of the house.
Heat, power, parts availability, safety, and practicality all must be considered, and worked out before going down this road. Any person contemplating a design of this magnitude should carefully evaluate their ability to complete the design safely.
As I mentioned before, I punted on the 4PR1000 amps, still have the hockey pucks (4CX250's) in my closet (for at least 15 years), and have put the 833A amps on hold due to a serious lack of time (I have indefinitely postponed projects of limited usefulness, even if they ARE cool). I actually gave away a 2KW RF linear that had a pair of 3-500Z's (with sockets) because I would not have gotten around to working on in the next few years, and the new owner has put it back on the air.
Now, back to my amp.
Yes, I know that this would be very difficult project as a starting point. I have seen this kind of audioamps in radiostations as modulator amplifiers. There was huge modulator transformer (output tr), it was almost 3 feet high monster. Well, it was anodemodulated PA so that transformer must handle full anode current.
It seems to be too difficult so let's forget those QBL's for this project. Originally these tubes was purposed for induction heater project that I designed and I think that's the project that these tubes will stay for.
Yes, I have very long experience about voltages of up to million volts and absolutely lethal current levels but I cannot say that it is safe hobby for me. It is not, never! These are always dangerous no matter who. I just like so much power electronics and specially vacuuntube stuff so have to take some risk and use lots of sense before plugging line voltages or so.
I can't stop my amplifier plans so now I need a lots of KT88's or similar power tubes for AUDIO use! Propably some TV sweep tubes will do the job also as those are rated for rather high anodecurrents/powers.
It seems to be too difficult so let's forget those QBL's for this project. Originally these tubes was purposed for induction heater project that I designed and I think that's the project that these tubes will stay for.
Yes, I have very long experience about voltages of up to million volts and absolutely lethal current levels but I cannot say that it is safe hobby for me. It is not, never! These are always dangerous no matter who. I just like so much power electronics and specially vacuuntube stuff so have to take some risk and use lots of sense before plugging line voltages or so.
I can't stop my amplifier plans so now I need a lots of KT88's or similar power tubes for AUDIO use!
Propably some TV sweep tubes will do the job also as those are rated for rather high anodecurrents/powers.
Although you may have done something with Tesla coils (the reference to "millions of volts") that's usually very different than the thousands of volts backed by several hundred milliamps or maybe an amp or two in terms of the effect on the human body. Instant death.
I'd steer clear of the high voltage/high current stuff for now, if I were you.
For modulation transformers, ask urself what is the difference between what you proposed and a modulation transformer?
Answer: Mod iron is usually P-P primary to single ended output, gapped core, AND more often than not a 2:1 impedance ratio or LESS between primary and secondary.
It is much much easier, although not easy, to wind a decent bit of iron when the ratios are close as opposed to something a 10Kohm or higher : 8 ohm!!
Fwiw, 6650s are usually less expensive than KT88s, although they are similar in spec, unless these are eastern euro "KT88s"...
Sweep tubes are good for high peak currents and higher plate voltages... but they're not triodes...
Consider some 845 sized tubes in PP AB2 for your higher power wishes?? Might be good for 200-350watts or so depending on how you use them...
It's hard to see why you'd really want or need SE for really high power stuff anyhow...
_-_-bear
I'd steer clear of the high voltage/high current stuff for now, if I were you.
For modulation transformers, ask urself what is the difference between what you proposed and a modulation transformer?
Answer: Mod iron is usually P-P primary to single ended output, gapped core, AND more often than not a 2:1 impedance ratio or LESS between primary and secondary.
It is much much easier, although not easy, to wind a decent bit of iron when the ratios are close as opposed to something a 10Kohm or higher : 8 ohm!!
Fwiw, 6650s are usually less expensive than KT88s, although they are similar in spec, unless these are eastern euro "KT88s"...
Sweep tubes are good for high peak currents and higher plate voltages... but they're not triodes...
Consider some 845 sized tubes in PP AB2 for your higher power wishes?? Might be good for 200-350watts or so depending on how you use them...
It's hard to see why you'd really want or need SE for really high power stuff anyhow...
_-_-bear
Yes, I have experienced also with teslacoils (more lethal than any tubeamp because of very high current/high voltage primarycircuit..>10kV/thousands of amps pulsed, >1A rms).
Most of my highvoltage experience comes from highpowered tube oscillators. 100W-10kW.
6000V/2A transformer stack:
transformers 1
0-5000V(200mA rms) variable supply:
transformer 2
Most of my highvoltage experience comes from highpowered tube oscillators. 100W-10kW.
6000V/2A transformer stack:
transformers 1
0-5000V(200mA rms) variable supply:
transformer 2
That first picture is absolutely scary. I am known as "extreme" and there is no way that I would get near that. Are you NUTS! One slip and you are TOAST!
Figure out how many watts you need (or want) and that you can get a transformer for. Then the tube selection will be easier. There was a thread here a while back showing pictures of a 1KW guitar amp using 4 X 813's in push pull. A pair of 833A's can produce over 2.5 KW of audio with forced air cooling and 3KV on the plates.
Figure out how many watts you need (or want) and that you can get a transformer for. Then the tube selection will be easier. There was a thread here a while back showing pictures of a 1KW guitar amp using 4 X 813's in push pull. A pair of 833A's can produce over 2.5 KW of audio with forced air cooling and 3KV on the plates.
Hey-Hey!!!,
There has to be a limit on just how big an output TX can get. No matter how complex the coil or how low-loss the core material. At some point there must be too much shunt capacitance and/or leakage L to deliver sublime sonics. I suspect it is somewhere near 100W for PP, less for SE.
cheers,
Douglas
There has to be a limit on just how big an output TX can get. No matter how complex the coil or how low-loss the core material. At some point there must be too much shunt capacitance and/or leakage L to deliver sublime sonics. I suspect it is somewhere near 100W for PP, less for SE.
cheers,
Douglas
I now use tiny little se amplifiers myself, but paralleling 6550/EL34 will get you several hundred watts at least before leakage L and shunt C become technically insurmountable issues. Witness the countless ARC amplifiers, VTL amplifiers, not to mention the Carver Silver 7 all of which manage obscene amounts of power and still make it to 20kHz if in some cases just barely..
The VTL Deluxe 300 was pretty good. I borrowed a pair to try with my MG1.6 Quasi-ribbons in the late 1990's. Pretty good sound, and authority I still find amazing.. 300Wrms monoblock fyi..
The VTL Deluxe 300 was pretty good. I borrowed a pair to try with my MG1.6 Quasi-ribbons in the late 1990's. Pretty good sound, and authority I still find amazing.. 300Wrms monoblock fyi..
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.