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#1
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To build or not to build
If everything works out this weekend I should have about 10w or so to
drive into a linear. My friend here in town thinks I should buy used Dentron Clipperton or Heathkit. I don't think 10watts would do either justice. If 10w would give me a KW out with a commercial unit I would consider buying a good used unit. Plan bravo is to build. I would have to do tubes in keeping with the theme of that side of the shack. CW, AM, & SSB are all modes that I would operate. I only need to operate 160m - 40m. I am experienced transistor engineer and my early schooling was in tubes , so not beyond my reach for this type of a project. I have plenty of other homebrew projects to keep me busy if this one gets scratched. I need help picking a topology and a tube set. Price and likelyhood of getting the thing working are two top runners. From the 1965 ARRL Handbook I see a few different tubes that might qualify. A Pair of 813 in parallel, 3-400Z, 3-1000Z. I am soliciting some opinions on the topology. Again, all I got is about 10w am going into. I would like to do a kw or so pep. I am not looking to buy any parts at this time, so not looking for any 'sales calls'. I need comments like - look at this tube with this plate voltage kinda thing. Or try driving this toob with a such and such to get a kw out. I would like to keep the design required to a minimum and would consider some 'reverse engineering' a plus at this point. If I can get most of the design out of an old ARRL handbook then that would please me. 73 Bob N9NEO |
#2
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To build or not to build
If everything works out this weekend I should have about 10w or so to
drive into a linear. My friend here in town thinks I should buy used Dentron Clipperton or Heathkit. I don't think 10watts would do either justice. If 10w would give me a KW out with a commercial unit I would consider buying a good used unit. ================= That's a 20dB amplification ...a bit much for a single stage amp. You need a 10 dB intermediate stage ,resulting in 100 W output. The final 10 dB to 1 kW can then be achieved with a (standard) Poweramp. Frank KN6WH / GM0CSZ |
#3
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To build or not to build
Highland Ham wrote:
If everything works out this weekend I should have about 10w or so to drive into a linear. My friend here in town thinks I should buy used Dentron Clipperton or Heathkit. I don't think 10watts would do either justice. If 10w would give me a KW out with a commercial unit I would consider buying a good used unit. ================= That's a 20dB amplification ...a bit much for a single stage amp. You need a 10 dB intermediate stage ,resulting in 100 W output. The final 10 dB to 1 kW can then be achieved with a (standard) Poweramp. Frank KN6WH / GM0CSZ The usual 6146 final stage doesn't take in more than a couple of watts for 100 watts out. I don't play with heavy iron, but AFAIK most linear amps are limited to 10dB of amplification because most hams have 100W output rigs and the FCC kinda frowns on non-home-built amps that can do more than that (something about CB'ers). I've seen tetrode amplifier designs that look like they could easily do this. You'd have to actually _pay attention_ to isolating the input from the output, and you'd have to do all the care-and-feeding stuff that screen grids require, but it should be possible to do it in one stage. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
#4
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To build or not to build
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#5
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To build or not to build
Frankly I don't think 10W will drive any linear to 1kW.
You will get the most gain from a Tetrode but I still don't think it will go 20db. I suggest you search for richard measures web page and read some of his articles about the merits of GG vs grid driven amplifiers. I think you will need an intermediate stage to get enough drive. Then you might as well pick up an old Heath SB200 or SB220 for the final stage. The SB200 will give you 500-600 watts out with a pair of 572s and you can buy them for 300 bucks. Plus the tubes are not too expensive if you need new ones. chuck |
#6
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To build or not to build
On Thu, 15 Dec 2005 04:42:33 +0000, Highland Ham
wrote: That's a 20dB amplification ...a bit much for a single stage amp. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ That's true in grounded grid mode, but quite doable for grid driven. According to the Amperex data sheet, a pair of 3-1000Zs in class B grid driven mode will give 3560 watts out for 28 watts of drive. For a single tube, that scales down to 127 watts out per watt in. 10 watts in will give 1270 watts out, a power gain of 21 dB. That's the only tube I've looked at so there may be others that will give a full 1500 out for 10 in. On the other hand, 1270 is close enough to 1500 that you'll probably never notice the difference. You will have to neutralize it of course, lest you end up with a high power VFO. :-) 73, Bill W6WRT |
#7
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To build or not to build
Chuck Sherwood wrote:
Frankly I don't think 10W will drive any linear to 1kW. You will get the most gain from a Tetrode but I still don't think it will go 20db. Most modern tetrodes will easily provide 20dB of gain, and with good stability. The favored technique is to use an untuned grid circuit which is resistively loaded (often called 'passive grid'). In class AB1, grid-driven, a tetrode requires very little RF input power (in simple theory, none at all). All the grid requires is a voltage swing. For good linearity, the tube should never be driven into grid current - in other words, even at peak RF input voltage the grid should never become positive. That means the peak RF voltage should only be equal to the grid's negative DC bias. These basic requirements are totally independent of the output power capability of the tube. For tube data, see: http://www.g8wrb.org/tetrodes.shtml The driver stage will need to see a 50 ohm load impedance, so the most common input circuit in commercial tetrode amplifiers is simply a 50 ohm resistor. However, 10W into 50 ohms is only 31V peak, and a typical value of grid bias is probably about -50V (depending on the specific type of tube and its recommended DC bias conditions). It is quite true that 10W could not drive such an amp to full output. But you're not forced to use a 50 ohm input resistor. Think about using a broadband step-up transformer to get a larger voltage swing. For example, a unun transformer with a 4:1 impedance step-up, terminated in a 200 ohm resistor. This will provide a 50 ohm load to the driver stage, and 10W will deliver about 62V peak to the grid of the tube. So any tube that will operate in class AB1 with a grid bias of 62V or less can be driven to full output by 10W. 10W into an input circuit consisting of a 9:1 unun terminated in 450 ohms will deliver about 93V peak. This is more than enough to drive any modern ceramic tetrode to full output, so the driver stage can actually be operated at significantly less than its 10W maximum, for improved intermodulation distortion. It should be quite easy to find or develop a suitable broadband transformer design, especially since the original poster only wanted to operate 160-40m. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
#8
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To build or not to build
In article ,
Ian White GM3SEK wrote: 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek Damn you guys are good. I need to hang out here more often! chuck |
#9
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To build or not to build
Ok, lots to think about here. I figured 20db would be a lot to ask
out of production unit. Tim's made a couple good points. A Tetrode may be a good way to go, but I wonder if a 4146 driving into something else might be a bit cheeper. Maybe a pair of 813s? As I said the 1965 ARRL handbook claims a kw out with a pair of 813s,but I have my doubts. They are cheep enough - $55 ea at tubesandmore.com The Taylor 572B can be had for about 200 bucks for 4 of em. Would this be a viable option? I wonder if the 4CX1000 or 3-1000Z solutions can be done for a good cost relative to other implementations. Also, are they easy to get working? I'm afraid I might end up chasing parasitic ghosts. I am aware that layout can be critical and would look to clone somebody elses design that's up and running if that's the way I go. Thanks for the comments. I thought it was narrowed down to a large tetrode with a lot of gain or two stages with 4146 maybe driving 813s or the 572Bs that get run in a lot of commercial rigs. Then I realized I would have to buy a plate transformer and a chassis and a box and a whole bunch of other stuff. Right about now some kinda intermediate predriver to get between the 10w out and the 100w in that I need might not be a bad deal. Then again I really need to buy from somebody I trust cause I hear a lot of people whining about used linears they bought. So nothing is decided. |
#10
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To build or not to build
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