RF Generator Mod. for 72-585
This updates the missing images for this modification. http://bleepmicro.livejournal.com/58080.html
IMPORTANT READ ME! I failed to show you how I was supplying power to the broadband amps power supply. I am pulling this rectified +24volts directly from the 2 diodes on the RF generators power supply. These are the primary diodes that power the generator, make sure you pull from the rectified side an not the center tapped transformer AC side. No need for a ground wire as the whole case is common grounded. Measure from case ground to these diodes and you should see about +24volts, you are at the right spot. !!Really My BAD!!
I needed a bit more output from my signal generator naturally leads to some sort of modification. Model is Tenma 72-585 Avg. price $160 Before the mod: Avg. 100mV up to 35MHz After the mod: 8v+ up to 80MHz (Much higher levels if you are fine with some distortion level) or basically 10mW up to 160mW depending on the transistor used and having parts to really design the amp for optimal performance. Nothing I do with this RF generator will ever go over 54Mhz. So, this mod works great for me. Let's begin.
BTW, total pull from my amp design was 60mA
1. Open the case. Pull off the atten knob, remove nut from the pot shaft. Remove the IDC cables plugged into the pcb and unsolder the crystal socket wires if your unit has this option as not all do. Now unsolder the BNC center pin from the pcb, then move over to the modulation input jack tabs an do the same. After these items are unsoldered and viewing the unit from the back side you should see a small metal tab on the right bottom side of the case that is holding the pcb corner, use a screwdriver or needle nose pliers and gently bend this tab out of the way to allow the pcb to be removed from the case easily.
2. Looking at the backside of the case with the pcb removed, you will notice that the case was designed to have two BNC type connectors installed, they just did not punch the front face plate for the second BNC. We are going to drill this out to install a new BNC connector. Here I used a standard metric uni-bit to drill mine out.
3. Once you have the hole drilled out on the front plate, insert the pcb back into the unit (DO NOT SOLDER IT BACK IN) just hold it in place by hand and from the front side use a pencil or sharpie to mark the front panel hole location onto the top of the pcb. Now remove the pcb and drill this center point for the center connection of the BNC. Take your time here and if you think it was not lined up straight then redo it, or else the center pin for the BNC will be off center. Also, be careful around these caps as they chip easily.
4. Along the bottom of the pcb there is a 0 ohm jumper that goes to the original BNC connector, remove this jumper. When view from the backside of the pcb if you drilled that hole correctly for the BNC connector and removed the 0 ohm jumper this is what it should look like.
5. Done with this part, reinstall the OEM pcb back into the case. (Notes: I switched the BNC. I used the original in the new hole we drilled as the post was longer and made it easier to get above the pcb as we did not cut out the front plate to recess the BNC connector. I also used a bit of 3M fiberglass tape across the backside of the BNC connectors, specifically around the ground tabs to help protect the disc capacitors on the board from damage).
6. Here is the board I created to hold the +24volt power supply and the broadband amplifier circuit. The ears are important due to the way the board is mounted onto the OEM board. The mass of the voltage regulator needed to be support very well, or it might cause the board to pull away if you just used the typical mounting of running a bead of solder across both pcb seams to try and hold it in place. Don't forget to scrape the green solder mask off the board.
7. Here I have built my test amp on some scrap pcb material first to allow for changing part values and locations.. etc. Much easier to work it out here then on the final board that will be mounted into the RF generator and it also keeps things looking nice. :-)
8. Here is the basic schematic, nothing new its just a basic broadband amp found in any RF/RADIO project book. No part values are given as I use scrap parts off of many types of boards. So, naturally the values will be different then if you were to built it with scrap board parts or design it properly with a spice program with near perfect values.
9. Here is my final version with everything tested and mounted onto the final board.
10. My amplifier board is tacked onto the OEM board and wired up for final checkout testing. I am pulling the drive signal directly off the pot adjustment tab, unit has no loading effect or weird harmonics. I recommend using shielded wire or coax for the connection from the pot tab to broadband amp input, this should help to keep things clean an prevent unwanted UHF oscillations. (Note: not shown is a small bit of copper mesh soldered onto the transistor as a heat sink. Keep in mind this adds capacitance to the collector of the transistor. I had already designed an tested my prototype with this heat sink before adding it to the final circuit, I just failed to visually document it for you. Violet wire goes to the +24v rectified side diodes on the main power supply for the generator.
11. I found the signal output from the broadband amp to be cleaner. Yes, I had to double check this to make sure the noise an distortion was not due to some loading of the RF oscillator being pulled off the output pot tab and it is was not the case... the RF Generator output is just that nasty. ( .16vp-p INPUT / 4vp-p OUTPUT @ about 20MHz)
12. DONE! Buttoned up and ready for some work.
Have fun!
* pcb=printed circuit board * BNC=Bayonet Neill-Concelman connector
Disclaimer: This information and the circuits are provided as is without any express or implied warranties. While every effort has been taken to ensure the accuracy of the information contained in this text, the authors/maintainers/contributors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.
I disclaim everything. The contents of the articles might be totally inaccurate, inappropriate, or misguided. There is no guarantee as to the suitability of said circuits and information for any purpose whatsoever other than as a self-training aid. I.E. If it blows your equipments, trashes your hard disc, wipes your backup, burns your building down or just plain don't work, IT ISN'T MY FAULT. In the event of judicial ruling to the contrary, any liability shall be limited to the sum charged on you by us for the aforementioned document or nothing, whichever is the lower.
I will not be held responsible for any damages or costs which might occur as a result of my advice or designs. All of my designs are allowed to be used for commercial purposes without my written authorization. Chemical Safety: Use of any and all Chemicals is simple “Read the damn Label” and don’t be a Hero or an Idiot. Use, Recycle, Reuse and Dispose of everything properly.
IMPORTANT READ ME! I failed to show you how I was supplying power to the broadband amps power supply. I am pulling this rectified +24volts directly from the 2 diodes on the RF generators power supply. These are the primary diodes that power the generator, make sure you pull from the rectified side an not the center tapped transformer AC side. No need for a ground wire as the whole case is common grounded. Measure from case ground to these diodes and you should see about +24volts, you are at the right spot. !!Really My BAD!!
I needed a bit more output from my signal generator naturally leads to some sort of modification. Model is Tenma 72-585 Avg. price $160 Before the mod: Avg. 100mV up to 35MHz After the mod: 8v+ up to 80MHz (Much higher levels if you are fine with some distortion level) or basically 10mW up to 160mW depending on the transistor used and having parts to really design the amp for optimal performance. Nothing I do with this RF generator will ever go over 54Mhz. So, this mod works great for me. Let's begin.
BTW, total pull from my amp design was 60mA
1. Open the case. Pull off the atten knob, remove nut from the pot shaft. Remove the IDC cables plugged into the pcb and unsolder the crystal socket wires if your unit has this option as not all do. Now unsolder the BNC center pin from the pcb, then move over to the modulation input jack tabs an do the same. After these items are unsoldered and viewing the unit from the back side you should see a small metal tab on the right bottom side of the case that is holding the pcb corner, use a screwdriver or needle nose pliers and gently bend this tab out of the way to allow the pcb to be removed from the case easily.
2. Looking at the backside of the case with the pcb removed, you will notice that the case was designed to have two BNC type connectors installed, they just did not punch the front face plate for the second BNC. We are going to drill this out to install a new BNC connector. Here I used a standard metric uni-bit to drill mine out.
3. Once you have the hole drilled out on the front plate, insert the pcb back into the unit (DO NOT SOLDER IT BACK IN) just hold it in place by hand and from the front side use a pencil or sharpie to mark the front panel hole location onto the top of the pcb. Now remove the pcb and drill this center point for the center connection of the BNC. Take your time here and if you think it was not lined up straight then redo it, or else the center pin for the BNC will be off center. Also, be careful around these caps as they chip easily.
4. Along the bottom of the pcb there is a 0 ohm jumper that goes to the original BNC connector, remove this jumper. When view from the backside of the pcb if you drilled that hole correctly for the BNC connector and removed the 0 ohm jumper this is what it should look like.
5. Done with this part, reinstall the OEM pcb back into the case. (Notes: I switched the BNC. I used the original in the new hole we drilled as the post was longer and made it easier to get above the pcb as we did not cut out the front plate to recess the BNC connector. I also used a bit of 3M fiberglass tape across the backside of the BNC connectors, specifically around the ground tabs to help protect the disc capacitors on the board from damage).
6. Here is the board I created to hold the +24volt power supply and the broadband amplifier circuit. The ears are important due to the way the board is mounted onto the OEM board. The mass of the voltage regulator needed to be support very well, or it might cause the board to pull away if you just used the typical mounting of running a bead of solder across both pcb seams to try and hold it in place. Don't forget to scrape the green solder mask off the board.
7. Here I have built my test amp on some scrap pcb material first to allow for changing part values and locations.. etc. Much easier to work it out here then on the final board that will be mounted into the RF generator and it also keeps things looking nice. :-)
8. Here is the basic schematic, nothing new its just a basic broadband amp found in any RF/RADIO project book. No part values are given as I use scrap parts off of many types of boards. So, naturally the values will be different then if you were to built it with scrap board parts or design it properly with a spice program with near perfect values.
9. Here is my final version with everything tested and mounted onto the final board.
10. My amplifier board is tacked onto the OEM board and wired up for final checkout testing. I am pulling the drive signal directly off the pot adjustment tab, unit has no loading effect or weird harmonics. I recommend using shielded wire or coax for the connection from the pot tab to broadband amp input, this should help to keep things clean an prevent unwanted UHF oscillations. (Note: not shown is a small bit of copper mesh soldered onto the transistor as a heat sink. Keep in mind this adds capacitance to the collector of the transistor. I had already designed an tested my prototype with this heat sink before adding it to the final circuit, I just failed to visually document it for you. Violet wire goes to the +24v rectified side diodes on the main power supply for the generator.
11. I found the signal output from the broadband amp to be cleaner. Yes, I had to double check this to make sure the noise an distortion was not due to some loading of the RF oscillator being pulled off the output pot tab and it is was not the case... the RF Generator output is just that nasty. ( .16vp-p INPUT / 4vp-p OUTPUT @ about 20MHz)
12. DONE! Buttoned up and ready for some work.
Have fun!
* pcb=printed circuit board * BNC=Bayonet Neill-Concelman connector
Disclaimer: This information and the circuits are provided as is without any express or implied warranties. While every effort has been taken to ensure the accuracy of the information contained in this text, the authors/maintainers/contributors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.
I disclaim everything. The contents of the articles might be totally inaccurate, inappropriate, or misguided. There is no guarantee as to the suitability of said circuits and information for any purpose whatsoever other than as a self-training aid. I.E. If it blows your equipments, trashes your hard disc, wipes your backup, burns your building down or just plain don't work, IT ISN'T MY FAULT. In the event of judicial ruling to the contrary, any liability shall be limited to the sum charged on you by us for the aforementioned document or nothing, whichever is the lower.
I will not be held responsible for any damages or costs which might occur as a result of my advice or designs. All of my designs are allowed to be used for commercial purposes without my written authorization. Chemical Safety: Use of any and all Chemicals is simple “Read the damn Label” and don’t be a Hero or an Idiot. Use, Recycle, Reuse and Dispose of everything properly.