The main resonator for the generator is a cavity which is course tuned by a movable internal plate over an octave range. The plastic cams are the limit stops which allow multiple turns of the course tuning knob before reaching the end. The lower frequency ranges are obtained by divider chain with each divider halving the frequency. The fine tuning to lock it to a frequency standard is by varacter. The lock method is called "huff-puff" stabilization. It use the frequency counter least significant bit output, via a low pass filter to slowly drift the frequency around an aiming point. This was designed before phase-locked loops were widely deployed at UHF frequencies. The best feature of the generator is it has very low phase noise and because of this the generator was often used as the interfering signal when evaluating adjacent channel, or intermodulation rejection on high quality receivers. Another nice feature is that a lot of internal signals can be routed to the front panel, so you can do things like use the frequency display to count an external RF signal.
I have the military version of this unit and the case is totally waterproof. There is a fellow on the HP equipment forum that sells replacement gears. Built like a tank.
Just thought you'd like to know approximately 32 years ago that signal generator cost $12,500. I have one, It's never been abused It still works perfectly and has Option 1, 2 and 3. I hope yours has the reverse power option. If you accidentally transmit into it by bumping the microphone when you're working on a transceiver you will nuke the attenuator assembly and the only way to fix it is to find another unit from a junker. The other issue with that generator is the nylon gears. There was a seller on eBay that was selling newly manufactured gears as a replacement. If any of yours are cracked it is not that hard to replace them. I always felt that this series of equipment was the Pinnacle of hp's Electro mechanical design.
I knew it had to be top of the line when it was new. I take the microphone off the radio before hooking up the HP, and double check the front panel TX switch, etc. One of the gears in this one have been patched with JB weld already. I'm thinking about trying to print nylon on my 3D printer and just making replacements. :-)
If you make replacements there will be many people that will want them. I have had 3 of these and all had this issue. I repaired one with epoxy and one with JB Weld. They both seemed to hold up fine.
Very informative Kevin! I found one similar to this at work years ago and now wish I had kept it. A tech friend in GA traded me a TM-741 tri band for it configured as 6,2 and 440, Still very valuable.
Man you are a lifesaver. thank you for the video and all the rest, a wealth of knowledge in just 20 mins! I just got on with opt 2 so it goes to 1.1GHz...fun fun
I was on a garage sale yesterday, after a hamradio operator who died recently, and paid 30$ for anything I could carry, and we could go as many times we wanted. I took two of these, plus alot of other instruments, like scopes, frequency counters ++++ For 30 bucks he he
Great little units Kevin. Again I love mine although it is not used as much. Good job on the power switch button. But keep that 3D printer warmed up. You may need it again. These units have a problem with the nylon frequency band gears. They crack due to the nylon shrinking. right across the set screw. This will lock the switch up. There was a guy in the UK that was making these from a mold. But do not think he is doing that now. There is also a brass mounting barrel in the center of the gear. So spend some time on Google searching HP8640b cracked gear. My first 3 videos was on this unit. Thanks for sharing Kevin.
Nice video Kevin, I'm a new subscriber to your channel and saw as you move the camera around your bench I noticed you had a set of IBM computer speakers that were sold back in the 90's. I have a pair of those that came with a IBM computer that I bought in 94. I now use them on my work bench too. 73's Jim
I found those. I walk daily and once in awhile some renter moves out and a bunch of boxes of stuff gets put out on the curb. My file server computer, an HP thin client that's a media player on my TV now, and a whole other computer system including two monitors all came from the curb. It's crazy what people throw out.
Looks similar Printed cover instructions like my BOONTON 102A signal gen.unfortunately the muppets at BOONTON decided to use a string cord assembly instead of the plastic cogs like it should have been.Still trying to re cord mine...a fkn nightmare.
I'm looking for one of these or a similar unit to perform alignments on AM-FM/FM Stereo tuners and tuner sections in stereo receivers and receiver preamps that clients send me to restore. Speaking generally, is the HP8640 with opt. 1 2 and 3 the best bang for the buck and capable enough to do proper alignments? I'm more of less sold on the HP units to go with my Hp8903B audio analyzer, and they never let me down. It would be great if on a future video you go thru a complete alignment/check for a AM-FM-FM Stereo receiver..perhaps one made before all the adjustments went away. I've looked at countless threads on countless forums, everyone has a different answer and most often the one your reading doesn't agree with the one you just read. More than that performing these kinds of alignments is a lost art. Surprisingly enough, no one has stepped up and demonstrated one that I've been able to find on TH-cam. Great Channel, I've liked and subscribed!
I have several 8640B's in my lab an d they are great. The one serious issue is the plastic gears used which crack and come apart with age. If you will look at 22:52 of your video, you will see the gear is cracked at the set screw. This may or may not be a problem for you later. It probably will depend how much you use the tuner in your unit. I have wondered if 3D printing is solid enough to make replacement gears for this application. I have not played with 3D printers yet but there are some really nice prices for basic units. ANy thoughts about printing those gears? 73, de Glenn WA4AOS
Nylon might be a viable material to print in. I haven't looked too closely at that gear yet. It might be possible, and might make for an interesting experiment. A lot depends on how fine of detail is needed for the gear teeth. It can be tough to get much strength in really thin or fine parts with certain materials. I might, if it's not too fine, print one in PLA on my printer and try it out.
Thanks for showing, Kevin. Electronics Revisited is an expert on these. He will repair them or sell completely rebuilt. The units he sells has the most commonly cracked gear (the lower differential gear in the RF/FM switch assembly) replaced with a metal one. He sells them rebuilt cheaper than some of the junkers on eBay. He offers some free tech. support if you need help with your own 8640B. Check out his website: www.electronicsrevisited.com/html/hp_8640b.html
The main resonator for the generator is a cavity which is course tuned by a movable internal plate over an octave range. The plastic cams are the limit stops which allow multiple turns of the course tuning knob before reaching the end. The lower frequency ranges are obtained by divider chain with each divider halving the frequency. The fine tuning to lock it to a frequency standard is by varacter. The lock method is called "huff-puff" stabilization. It use the frequency counter least significant bit output, via a low pass filter to slowly drift the frequency around an aiming point. This was designed before phase-locked loops were widely deployed at UHF frequencies. The best feature of the generator is it has very low phase noise and because of this the generator was often used as the interfering signal when evaluating adjacent channel, or intermodulation rejection on high quality receivers. Another nice feature is that a lot of internal signals can be routed to the front panel, so you can do things like use the frequency display to count an external RF signal.
Thanks for taking the time to supply all of that info. I've pinned your comment to the top so others will see it first.
It was a nice signal generator. in that years. My unit only had a knob broken problem. Love it.
I have the military version of this unit and the case is totally waterproof. There is a fellow on the HP equipment forum that sells replacement gears. Built like a tank.
I just replaced the gears in mine.
Used the HP 8640b for many years working for the US Government as a tech...............Loved it!
Just thought you'd like to know approximately 32 years ago that signal generator cost $12,500. I have one, It's never been abused It still works perfectly and has Option 1, 2 and 3. I hope yours has the reverse power option. If you accidentally transmit into it by bumping the microphone when you're working on a transceiver you will nuke the attenuator assembly and the only way to fix it is to find another unit from a junker. The other issue with that generator is the nylon gears. There was a seller on eBay that was selling newly manufactured gears as a replacement. If any of yours are cracked it is not that hard to replace them. I always felt that this series of equipment was the Pinnacle of hp's Electro mechanical design.
I knew it had to be top of the line when it was new. I take the microphone off the radio before hooking up the HP, and double check the front panel TX switch, etc. One of the gears in this one have been patched with JB weld already. I'm thinking about trying to print nylon on my 3D printer and just making replacements. :-)
If you make replacements there will be many people that will want them. I have had 3 of these and all had this issue. I repaired one with epoxy and one with JB Weld. They both seemed to hold up fine.
Very informative Kevin! I found one similar to this at work years ago and now wish I had kept it. A tech friend in GA traded me a TM-741 tri band for it configured as 6,2 and 440, Still very valuable.
teardown
Thanks Kevin! I have the 8640A and played with it while you were walking through the B. Very helpful! 73, John/N6VTS
Currently watching an 8640B in USAF livery on an auction site. I think you have helped me make a decision...
Used those years ago when in the Navy. I wish I had one.
i have one i will sell you for 100.00
Man you are a lifesaver. thank you for the video and all the rest, a wealth of knowledge in just 20 mins! I just got on with opt 2 so it goes to 1.1GHz...fun fun
I was on a garage sale yesterday, after a hamradio operator who died recently, and paid 30$ for anything I could carry, and we could go as many times we wanted. I took two of these, plus alot of other instruments, like scopes, frequency counters ++++ For 30 bucks he he
Great little units Kevin. Again I love mine although it is not used as much. Good job on the power switch button. But keep that 3D printer warmed up. You may need it again. These units have a problem with the nylon frequency band gears. They crack due to the nylon shrinking. right across the set screw. This will lock the switch up. There was a guy in the UK that was making these from a mold. But do not think he is doing that now. There is also a brass mounting barrel in the center of the gear. So spend some time on Google searching HP8640b cracked gear. My first 3 videos was on this unit. Thanks for sharing Kevin.
This one's already had the gears patched with epoxy. But if they fail again, I'll just 3D print replacements. ;-)
Nice video Kevin, I'm a new subscriber to your channel and saw as you move the camera around your bench I noticed you had a set of IBM computer speakers that were sold back in the 90's. I have a pair of those that came with a IBM computer that I bought in 94. I now use them on my work bench too. 73's Jim
I found those. I walk daily and once in awhile some renter moves out and a bunch of boxes of stuff gets put out on the curb. My file server computer, an HP thin client that's a media player on my TV now, and a whole other computer system including two monitors all came from the curb. It's crazy what people throw out.
Looks similar Printed cover instructions like my BOONTON 102A signal gen.unfortunately the muppets at BOONTON decided to use a string cord assembly instead of the plastic cogs like it should have been.Still trying to re cord mine...a fkn nightmare.
wow....maybe it is a hydraulic RF generator because of the rigid lines inside hi hi :-)
Thanks for showing us also the inside view.
73
I'm looking for one of these or a similar unit to perform alignments on AM-FM/FM Stereo tuners and tuner sections in stereo receivers and receiver preamps that clients send me to restore. Speaking generally, is the HP8640 with opt. 1 2 and 3 the best bang for the buck and capable enough to do proper alignments? I'm more of less sold on the HP units to go with my Hp8903B audio analyzer, and they never let me down. It would be great if on a future video you go thru a complete alignment/check for a AM-FM-FM Stereo receiver..perhaps one made before all the adjustments went away.
I've looked at countless threads on countless forums, everyone has a different answer and most often the one your reading doesn't agree with the one you just read. More than that performing these kinds of alignments is a lost art. Surprisingly enough, no one has stepped up and demonstrated one that I've been able to find on TH-cam. Great Channel, I've liked and subscribed!
Try checking Mr. Carlson’s Lab here on TH-cam. He does lots of alignments on all kinds of gear. I love his videos on the 1970’s pioneer receivers.
Nice job !
I have several 8640B's in my lab an d they are great. The one serious issue is the plastic gears used which crack and come apart with age. If you will look at 22:52 of your video, you will see the gear is cracked at the set screw. This may or may not be a problem for you later. It probably will depend how much you use the tuner in your unit.
I have wondered if 3D printing is solid enough to make replacement gears for this application. I have not played with 3D printers yet but there are some really nice prices for basic units.
ANy thoughts about printing those gears?
73, de Glenn WA4AOS
Nylon might be a viable material to print in. I haven't looked too closely at that gear yet. It might be possible, and might make for an interesting experiment. A lot depends on how fine of detail is needed for the gear teeth. It can be tough to get much strength in really thin or fine parts with certain materials. I might, if it's not too fine, print one in PLA on my printer and try it out.
Nice job
Thanks for showing, Kevin. Electronics Revisited is an expert on these. He will repair them or sell completely rebuilt. The units he sells has the most commonly cracked gear (the lower differential gear in the RF/FM switch assembly) replaced with a metal one. He sells them rebuilt cheaper than some of the junkers on eBay. He offers some free tech. support if you need help with your own 8640B. Check out his website:
www.electronicsrevisited.com/html/hp_8640b.html
I think those tabs are just a mechanism to allow 10 revolutions, then stop. They are too floaty to be turning anything inside
Correct!
Yep. The R-390A receiver has a pair of them, but made from metal discs, not plastic.
ممكن اعرف عمل هذا لجهاز
That is not the signal generator with the Easter egg I don't think.