Amplifier ideas
I am re-visiting an amplifier construction project. I have been thinking about building an amp for quite some time. It would be an excellent piece of home-brew gear in the shack and it is the only piece of equipment I don't have (minus various test equipment. I have rigs, a tuner/transmatch/impedance matcher (HI - read my post on tuners from a couple months ago), power supply, coax, and antennas. The only piece of gear (in the transmit/receive line) I don't have is an amp.
I'll be right up front with this - I don't, at this moment in time, have the knowledge to build an amp. I do have the knowledge, ambition, and desire to learn how to do it. I just got my Extra class license in the past month or so. That said, the reason for revisiting the project is because I have a RARE opportunity at hand. I am a student at OSU and have a professor who is a ham and has enough knowledge and electronics experience to guide me through it. I am taking his design class this winter (and his 1st electronics course in the spring) and have the OK on the amp for my project. I knew this was a possibility about half way through last quarter, so I have been researching things with this project in the back of my mind since then. Now that school started back up this is all starting to roll!
The project details aren't laid down yet. That is what I am in the process of - and partially why I wrote this post. Please feel free to e-mail or comment with any suggestions.
I work the HF bands mostly, but I am an avid VHF'er (if you have read a few of my other posts on here then you know what I mean HI). I would like to cover all bands QRO. Right now I can get on 160-2m and 70cm. I know this is impossible to cram in to one amp because of the differences in circuit design (component values/sizes). I know I can get 160-10m in one box. There are a zillion 160-10m amp designs out there. Everything from a few tens of watts to legal limit and then some, transistors and tubes alike. However, I can't say that I have ever seen a tube amp covering 160-6m that is QRO. If I am going to build an amp then I would much rather build an AMP - legal limit. I can always knock the power down, but I can't go the other way.
Transistors would be GREAT to use - they are tiny, light weight, and more reliable in service than a tube (given they are used within their specs). The down side is they are VERY EXPENSIVE!!!!!!! That is a major issue. So, I am going to resort to using a tube. This isn't a bad deal, though. Tubes are very popular (more so than transistors, probably because of the cost issue) so there are many to choose from and many places to get them.
Right now, I have a 3cx/3cpx1500A7 (8877) in mind. Just one is all I need and I won't need to run it "hot" for legal limit. This is subject to change, however. I need to track one down first. If you know where I can get a (working) pull for cheap let me know!
I want to cover 160-6m. Now, if you build or have any knowledge about amps, I know what you are probably thinking - I'm crazy. Well, yes, maybe a little. I know 10/12m are hard to tune. Getting to 6m is going to be even harder. An 8877 will run up to 2m, maybe 1.25m, so the tube isn't the problem. Getting the tank to resonate on 6m, while also down on HF, is going to be a real trick. I will have to dig in to the circuitry design to see what my options are.
As part of the design I want to have expandable, separate boxes, for the VHF+ bands. This means the amp should be rack mountable - most likely 19" since that is the "standard". The power supply can probably be shared between all the other boxes, so that would keep the cost and build effort down on the expansion bands. I don't know if I want to build the power supply in to the HF amp or not. If I do then I have one self-contained unit, which would simplify mobility for operating events like field day and other contests. That would also, most likely, take up less space on the rack than having two boxes. The amp/ps combo would be bigger than just the amp or ps box, however.
If you did read this, or just skimmed over it, and have any suggestions/comments, whatever, PLEASE let me know! All input is greatly appreciated. Leave a comment (preferred so I can post it on the site for others to read) or e-mail me: sjdamico@gmail.com
Edit 1/6/08:
I am researching HF/6m tube amps to see what I can come up with. I am going to compile a list below for my own records but surely others will benefit from my research. This should be an interesting search!
ACOM1000 single GU-74b 1000w
N4IS amp homebrew - looks like a pair of 3cx800's, no construction/spec details
Edit 1/20/08:
I think I am going to switch over to a GS-35b tube instead. They are a lot cheaper than an 8877 (even a pulled one) and I should be able to get 1500w out of one. I can also use them all the way up through the UHF bands.
I have a PS. I am not sure of the specs and don't have a schematic of it, though. I know it came from a Motorola repeater and the big transformer is 3500v on the secondary. I was told it was in a Micor repeater, of what era I am not sure.
If you have or know where I can get a schematic and all the specifications of this PS I would greatly appreciate it!
I'll be right up front with this - I don't, at this moment in time, have the knowledge to build an amp. I do have the knowledge, ambition, and desire to learn how to do it. I just got my Extra class license in the past month or so. That said, the reason for revisiting the project is because I have a RARE opportunity at hand. I am a student at OSU and have a professor who is a ham and has enough knowledge and electronics experience to guide me through it. I am taking his design class this winter (and his 1st electronics course in the spring) and have the OK on the amp for my project. I knew this was a possibility about half way through last quarter, so I have been researching things with this project in the back of my mind since then. Now that school started back up this is all starting to roll!
The project details aren't laid down yet. That is what I am in the process of - and partially why I wrote this post. Please feel free to e-mail or comment with any suggestions.
I work the HF bands mostly, but I am an avid VHF'er (if you have read a few of my other posts on here then you know what I mean HI). I would like to cover all bands QRO. Right now I can get on 160-2m and 70cm. I know this is impossible to cram in to one amp because of the differences in circuit design (component values/sizes). I know I can get 160-10m in one box. There are a zillion 160-10m amp designs out there. Everything from a few tens of watts to legal limit and then some, transistors and tubes alike. However, I can't say that I have ever seen a tube amp covering 160-6m that is QRO. If I am going to build an amp then I would much rather build an AMP - legal limit. I can always knock the power down, but I can't go the other way.
Transistors would be GREAT to use - they are tiny, light weight, and more reliable in service than a tube (given they are used within their specs). The down side is they are VERY EXPENSIVE!!!!!!! That is a major issue. So, I am going to resort to using a tube. This isn't a bad deal, though. Tubes are very popular (more so than transistors, probably because of the cost issue) so there are many to choose from and many places to get them.
Right now, I have a 3cx/3cpx1500A7 (8877) in mind. Just one is all I need and I won't need to run it "hot" for legal limit. This is subject to change, however. I need to track one down first. If you know where I can get a (working) pull for cheap let me know!
I want to cover 160-6m. Now, if you build or have any knowledge about amps, I know what you are probably thinking - I'm crazy. Well, yes, maybe a little. I know 10/12m are hard to tune. Getting to 6m is going to be even harder. An 8877 will run up to 2m, maybe 1.25m, so the tube isn't the problem. Getting the tank to resonate on 6m, while also down on HF, is going to be a real trick. I will have to dig in to the circuitry design to see what my options are.
As part of the design I want to have expandable, separate boxes, for the VHF+ bands. This means the amp should be rack mountable - most likely 19" since that is the "standard". The power supply can probably be shared between all the other boxes, so that would keep the cost and build effort down on the expansion bands. I don't know if I want to build the power supply in to the HF amp or not. If I do then I have one self-contained unit, which would simplify mobility for operating events like field day and other contests. That would also, most likely, take up less space on the rack than having two boxes. The amp/ps combo would be bigger than just the amp or ps box, however.
If you did read this, or just skimmed over it, and have any suggestions/comments, whatever, PLEASE let me know! All input is greatly appreciated. Leave a comment (preferred so I can post it on the site for others to read) or e-mail me: sjdamico@gmail.com
Edit 1/6/08:
I am researching HF/6m tube amps to see what I can come up with. I am going to compile a list below for my own records but surely others will benefit from my research. This should be an interesting search!
ACOM1000 single GU-74b 1000w
N4IS amp homebrew - looks like a pair of 3cx800's, no construction/spec details
Edit 1/20/08:
I think I am going to switch over to a GS-35b tube instead. They are a lot cheaper than an 8877 (even a pulled one) and I should be able to get 1500w out of one. I can also use them all the way up through the UHF bands.
I have a PS. I am not sure of the specs and don't have a schematic of it, though. I know it came from a Motorola repeater and the big transformer is 3500v on the secondary. I was told it was in a Micor repeater, of what era I am not sure.
If you have or know where I can get a schematic and all the specifications of this PS I would greatly appreciate it!
posted by Steve at
6:05 PM
4 Comments
