Hey All,
I got myself two of these 17gv5 tubes at a swap meet. I'm interested in making them into a push pull amp. I'm curious what my options are. I'd like to design my own circuit from scratch rather than build a kit. I have been reading around on valvewizard about push pull design, and its helping me get the general idea about what I need to consider. However he makes a lot of decisions for guitar amps. Is there a good resource where I could learn how to design a push pull amp for HiFi?
I don't care too much about the fact that these tubes are sweep tubes and how they will sound, I'm not trying to build the best amp ever just the best amp I can with the tubes I have. My goal is to design the best PP output I can with these two tubes, If I like how it sounds then I'll get some more and make the second channel.
Thanks!
I got myself two of these 17gv5 tubes at a swap meet. I'm interested in making them into a push pull amp. I'm curious what my options are. I'd like to design my own circuit from scratch rather than build a kit. I have been reading around on valvewizard about push pull design, and its helping me get the general idea about what I need to consider. However he makes a lot of decisions for guitar amps. Is there a good resource where I could learn how to design a push pull amp for HiFi?
I don't care too much about the fact that these tubes are sweep tubes and how they will sound, I'm not trying to build the best amp ever just the best amp I can with the tubes I have. My goal is to design the best PP output I can with these two tubes, If I like how it sounds then I'll get some more and make the second channel.
Thanks!
You can try Merlin's new Preamplifier book and Morgan Jones' book, if you want free resources, you can download Norman Crowhurst's Hi-Fi design books and papers.
I've been considering the engineer's amp as a backup option, I'd only have to modify the heater supply to work with the tubes I have. My only reservation about that is that I like the design process associated with making the whole thing from scratch, even if that means that my amp will be simpler and less effective than something someone else designed.
I've built one tube amp before, it was a single ended 6v6 amp that was all my own design. While that amp works fine I'm looking to make something with more power to push a standard pair of speakers, with better fidelity and low end response.
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Instead of just jumping in, have you at least studied some classic designs and really understand the circuits? Can you read the schematics and tell what the functional blocks are doing?
Yeah so I should clarify, at this point I'm very comfortable with tube designs. I'm a 4th year EE student at this point, so all of this pulls on material that I've recently learned and is still fresh in my mind. I spent a good amount of time with material from Merlin, here, and /r/diytubes learning how to make my first amp (which was a single ended design). The process of designing and building that amp taught me a lot about tube amp design, so at this point I'm pretty good at understanding what is happening in tube schematics.
Honestly I know I could make a push pull amp, I understand the theory to a point where I know I could design something all on my own that would work. However there are still a lot of small things that I don't know; I don't particularly understand feedback analysis, and due to limited funds I can't really experiment with a whole bunch of valves to see how they behave. So everything I know comes form seeing other designs, my own limited experiments, school, or reading material online.
All of these things would cause my design to be ok, but I wan't to make something great.
I could just make the engineer's amp, and I know it would be good, and I'd probably love it to death. But half the fun of this hobby, for me, is building the whole thing myself from schematic to finished product.
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It is an interesting tube, but to get reasonable power from a pair in pentode connection, an output transformer with 15-17 K primary will be needed.
Ok so that's interesting, how do you figure that? That would make finding a suitable transformer difficult.
17GV5 is the same tube inside as 6JN6 or 6GE5 (except for plate cap, heater V, base pinout). They are capable of 550 mA peak cathode current, well above most "audio" 6L6 like tubes.
6JN6 was used with Pete Millett's DCPP amplifier using an 8K primary OT. Many considered 8K on the high side even, but that was so the driver distortion could cancel with the (now lowish) output tube distortion. George (Tubelab) used them with 3.3K OTs and got good results. Maybe 4K or 5K primary Z would be considered a nominal OT.
Since they have the same basing as 6/16/21GY5, you might want to also try a couple of those in the same amplifier for kicks. (800 mA peak, 18 Watt). (all just $3 tubes, Vacuumtubes.net or ESRCvacuumtubes.com)
Nothing wrong with the TV Sweeps, just using lower primary Z and lower B+ typically (than 6L6 types).
If you don't want plate caps, then the 6/12GE5 or 6/12JN6 are the same tube as 6/17GV5.
6/21HB5 is the capless version of the 6/21GY5. 6/12GE5 and 6/21HB5 use the same base pinout for interchangeability. (all are like $6 tubes in certain heater V types)
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6JN6 was used with Pete Millett's DCPP amplifier using an 8K primary OT. Many considered 8K on the high side even, but that was so the driver distortion could cancel with the (now lowish) output tube distortion. George (Tubelab) used them with 3.3K OTs and got good results. Maybe 4K or 5K primary Z would be considered a nominal OT.
Since they have the same basing as 6/16/21GY5, you might want to also try a couple of those in the same amplifier for kicks. (800 mA peak, 18 Watt). (all just $3 tubes, Vacuumtubes.net or ESRCvacuumtubes.com)
Nothing wrong with the TV Sweeps, just using lower primary Z and lower B+ typically (than 6L6 types).
If you don't want plate caps, then the 6/12GE5 or 6/12JN6 are the same tube as 6/17GV5.
6/21HB5 is the capless version of the 6/21GY5. 6/12GE5 and 6/21HB5 use the same base pinout for interchangeability. (all are like $6 tubes in certain heater V types)
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The 6GV5's that I stuffed into Pete's Big Red Board will gladly give you 50 watts forever on about 450 volts with a 6.6K ohm load. About 70 watts can be had with a 5K load, and of course more power can be had with more voltage.
Don't want to use Pete's board. I would still study the design, and the one I did for the 6L6GC in AB2 thread. Either could be used for a sweep tube amp build in the 125 WPC and under range.
Posted new P-P power amp design
6L6GC AB2 Amp
By drawing load line. Data sheet has plate curves for Ug2=150 V, so it has to be extrapolated to 200 V. Idle operating point is 600 V plate, 200 V screen, -40 V control grid, 25 mA plate current.
One only would need 200V for grid 2 if requiring very high plate currents. Which would certainly exceed the 17.5 Watt rating using 600V.
150V on grid 2 is nominal for TV Sweep tubes, except for maybe some 40 Watt ones. Distortion is always lower with lower Vg2 since the plate curve kinks drop to lower plate V and get smaller too. (so out of the way of the load line)
You want to use only sufficient Vg2 to get the max current needed on the chosen load line. (which needs to obey the max plate dissipation ratings)
150V on grid 2 is nominal for TV Sweep tubes, except for maybe some 40 Watt ones. Distortion is always lower with lower Vg2 since the plate curve kinks drop to lower plate V and get smaller too. (so out of the way of the load line)
You want to use only sufficient Vg2 to get the max current needed on the chosen load line. (which needs to obey the max plate dissipation ratings)
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Agree that 150 V on screen will be safer and result in less distortion. But with 150 V screen, optimal plate load well be even higher. The higher the Ua/Ug2 ratio, the higher the load.
I have been working with TV sweep tubes since the 1960's, when they were essentially free. Tons of discarded TV sets were available by visiting the local trash dump.
I have built P-P amps with sweep tubes from the tiny 6GF5 to the big fat 6LW6. I have never used an OPT of more than 6600 ohms. The little 6GF5 will put 40 watts into 6600 ohms on 400 volts, and 70 watts if you choose to ignore the ratings and crank up the voltage (they don't blow up).
The big boys like 6LR6 and 6LW6 will work down to 2500 ohms. The lower the impedance, the higher the output power for a given plate voltage. In almost every case I use 150 volts on G2. Some of the older sweep tubes may need a bit more voltage.
When tuning for max power, you MUST watch the maximum peak cathode current spec. That determines the lower limit on load impedance, and idle plate dissipation determines the upper limit on plate voltage.
The 6HJ5 is at both limits on 625 volts into 3300 ohms where a pair delivers 125 watts. At least a dozen of these were built in Pete's Big Red Board thread. Both of mine still have their original tubes in them, and I play my guitar through one of them
Right now I'm working on the design of a 1 KW sweep tube amp (500 WPC). If I choose to use a conventional G1 driven P-P topology I'm looking at 4 to 6 X 36LW6's on 650 to 700 volts into a 1250 ohm OPT. I am currently exploring some rather unusual output stage topologies to improve efficiency. Getting 1KW of audio from a US spec wall outlet (1800 watts) is tough when you burn 200+ watts in tube heaters. I also need to be able to lift this thing. I'm in a basement, and I'm not getting any younger!
I have built P-P amps with sweep tubes from the tiny 6GF5 to the big fat 6LW6. I have never used an OPT of more than 6600 ohms. The little 6GF5 will put 40 watts into 6600 ohms on 400 volts, and 70 watts if you choose to ignore the ratings and crank up the voltage (they don't blow up).
The big boys like 6LR6 and 6LW6 will work down to 2500 ohms. The lower the impedance, the higher the output power for a given plate voltage. In almost every case I use 150 volts on G2. Some of the older sweep tubes may need a bit more voltage.
When tuning for max power, you MUST watch the maximum peak cathode current spec. That determines the lower limit on load impedance, and idle plate dissipation determines the upper limit on plate voltage.
The 6HJ5 is at both limits on 625 volts into 3300 ohms where a pair delivers 125 watts. At least a dozen of these were built in Pete's Big Red Board thread. Both of mine still have their original tubes in them, and I play my guitar through one of them
Right now I'm working on the design of a 1 KW sweep tube amp (500 WPC). If I choose to use a conventional G1 driven P-P topology I'm looking at 4 to 6 X 36LW6's on 650 to 700 volts into a 1250 ohm OPT. I am currently exploring some rather unusual output stage topologies to improve efficiency. Getting 1KW of audio from a US spec wall outlet (1800 watts) is tough when you burn 200+ watts in tube heaters. I also need to be able to lift this thing. I'm in a basement, and I'm not getting any younger!
From your power outputs I reckon it is AB2, which works optimally with lower loads than AB1. Class A will require even higher load than AB1.
Grid current is not usually needed to reach the maximum peak cathode current limitation on most sweep tubes.
Most of my experiments were carried out on one of Pete's boards and the data is scattered throughout the associated thread. The board was not designed to support AB2 operation although I did observe the grid going slightly positive on some experiments.
> never used an OPT of more than 6600 ohms.
The 6GV5 data show it can support a swing from 250V (65mA) to 60V at 345V. A 190V swing at 345mA is 550 Ohms per plate, or 2,200CT Ohms the way we specify an output transformer.
250V to 60V means 24% of B+ is wasted. The DC supply "can" be higher; 250V was a cost-point in TV design. If we apply 600V, only 10% waste. This is 90W output, so is likely to exceed Pdiss (even the higher limit in linear work). But it does mean a 6,300CT OT, in line with Tubelab's work.
All this without G1 current ("AB2") because TV sweep circuits hate grid current at least as much as modern audio circuits do. Even if you can avoid cap-coupling, you need a hefty driver. In audio and TV, work was done to extend the no-G1-current ability.
The 6GV5 data show it can support a swing from 250V (65mA) to 60V at 345V. A 190V swing at 345mA is 550 Ohms per plate, or 2,200CT Ohms the way we specify an output transformer.
250V to 60V means 24% of B+ is wasted. The DC supply "can" be higher; 250V was a cost-point in TV design. If we apply 600V, only 10% waste. This is 90W output, so is likely to exceed Pdiss (even the higher limit in linear work). But it does mean a 6,300CT OT, in line with Tubelab's work.
All this without G1 current ("AB2") because TV sweep circuits hate grid current at least as much as modern audio circuits do. Even if you can avoid cap-coupling, you need a hefty driver. In audio and TV, work was done to extend the no-G1-current ability.
Can you "design" a skyscraper or e.g. a bridge with zero experience? You answer to yourself.
So, actually, "a kit" would be the best way to start, well, with some tweaks considering you bought into the odd 17V heating, otherwise the tube is great. You can really make a masterpiece out of it if you have a knowledge, which seems not being a case. ..
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