For the past few months I have been building an Ultra Probe. I have little experience with surface mount stuff, but have been giving it a shot. The circuit boards (for the amp and probe) are just my second attempt at toner transfer. The probe CB came out perfect, but the amp PC had some filled drill holes and a trace that was missing. I just soldered a #30 AWG wire in place of the trace. I’ve been using my 25 watt iron to solder in the parts. Feels like my 300 watt American Beauty, but works for the most part. I did have 3 or 4 bad solder joints and I did melt one of the little red LED’s. Made a box and installed the speaker, controls, switches and board, but had no room for the batteries (speaker too large). So, I placed a phono jack on the side and plug in the batteries that way. I didn’t have a switch on the VR anyway and didn’t want to purchase one. Tried the toner transfer to shipping label, worked pretty good. In the old days I used dry transfer lettering, works about the same, except you have to make your program to the correct dimensions. That took a few tries. Well got the box closed up and powered up, takes about 20 ma, seems OK. Then I placed a 6 inch wire into the BNC connector and with the switch on detect, I could receive every radio station in the area, all at once, with tons of volume. Started on making the probe, but that will take a few more days. Let you know.
Hi, as for the batteries fitment, you can try to split them in 2 bunches and put 1 bunch on each side of the speaker. I did the same on my build and it just about fitted it. But mind you, the Hammond box (I used is about half the size MCL used) and had to use smaller 1.2V rechargeable (Panasonic Enelope) batteries as well as re-designing the whole PCB from scratch (to make it all fit to that little box that I already had as spare) but managed to fit them all inside… in the end :)) It took me a couple of design variants to achieve the desired results but it turned out great.
I’m having a devil of a time with all these small parts and close quarters. The Amplifier is finish and seems to work right. But I’m having trouble getting the cables into the probe without shorting things out. After a few times I think it is coming. I think my main problem is that I used some RG400 which I had and maybe should have gotten some small coax. It’s coming.
Well…… I finally got this thing (I believe) to work. The speaker works when the probe is near my hand and so does the Indicator. One thing I’m a little confused about is the gain control. I would have thought that by changing the gain the volume would increase, but so far I can not detect any change. I do measure that the voltage does change as the gain control is moved. I want to try out the probe on something and see what it does. I think I need to re watch the videos. Let you know. Thanks for the help.
Well while attempting to test the probe, I have discovered that I made some bad choices regarding the probe cables. I was attempting to use RG400 coax, because it was something I had, but after horsing around with it for the past few days, It is too big in diameter and very inflexible for a probe cable. I will need to find something smaller. Then the 2 wire insulated power cable was also a poor choice. The insulation just melts away then I attempt to solder it anything, resulting a short at the probe, where the cables go through the end. So, I need to find some better cables. Smaller diameter coax and better insulation on the 2 wire shield cable. I will also have to get some BNC connectors that will work for what ever RG?? I get. Every time I build something there seems to be the one step forward and then 2 steps back rule comes in force, but I also seem to learn a few lessons. Now if I can only remember them for the next time. Need to find some stuff order it and hopefully the probe will work much better. Mike
@mike-zahorik Hi. For the signal a really good choice would be the RG316 coax cable that is small in diameter (only 2.5mm diameter) or a good second option is find an old oscilloscope probe that you will no longer use. They are specifically made using a very small diameter and extremely flexible coax and the advantage is is that the BNC is already fitted at one end. Another option for a thin and flexible coax is the RG 174. this is also about 2.5mm in diameter and even more flexible that the RG316. As for the supply voltage one option would be to use the shielded cable from an old pair of a stereo headphones or from an audio (RCA plugs) cable or… use the internal shielded cable from an old HDMI or similar cable etc etc. Good luck and keep on posting your progress. I am pretty sure that your ”swings and roundabouts” / ‘hurdles” will greatly and certainly help other beginner builders too 🙂
@ovi4 Well, I obtained a length of RG174 and I believe that I have it installed properly. There is enough room to get both cables through the probe hole. Since then I have had to repair a couple other problems that I uncovered. First I wired the gain pot backwards, so when the control is fully CCW the voltage on the probe is maximum. This was a job in that I had to remove the CB to gain access to the VR. Then I noticed that the detect circuit seemed to work just fine. I could receive local radio stations with an antenna connected, but the audio circuit would not work. This meant that the speaker amp was working but some thing was wrong with the 4066 switches. Rats! So to get the old IC out, I decided to cut the IC leads with a razor knife and then brush away the remaining lead from each pad. This actually worked pretty good. Then I had to install the new IC. I have a lot of trouble with these surface mount parts. They are so small, my tools (25 watt soldering iron) seem so large and my eyes so bad (78 year old eyes), but I got the damned thing in and I now believe the amplifier now works correctly. Next I have to test the probe. Any ideas of hints on a good way of testing the probe. I was thinking that if I turned on my signal generator and brought the probe close to it I should hear the audio on the high frequency, in the detect mode. How would I test the audio mode? Thanks for the help, Mike
@mike-zahorik I’m glad you finally got all hurdles sorted. well…to test the audio should be a simple task, sniff near any audio device near the volume pot or thru stages of a preamp (transistor by transistor) till the final output stage or a phono preamp stage etc. It could also be an earphone amp. a CD player, or a simple portable radio. The world is your oyster. 🙂
@mike-zahorik Great job working your way through it! Practice makes perfect (or closer to it). I have a large list of projects I need to build myself, one thing at a time.
Radios + Tubes + Scopes + Cars= Nothing better!
Well, hold off on the accolades. Since I started testing my probe, I’ve been struggling. Not that the circuit is giving me trouble, at least now, it is the probe case. I purchased a couple of the solder suckers for the case. I got the circuit board to fit just fine and with the smaller coax, I had thought I’m on easy street. Started testing and all I got was noise. Turns out I can not make a good connection to the aluminum case. I get the circuit board soldered just fine to the small brass insert, but not to the aluminum. Without a good connection here, each time I pick up the probe the amplifier howls and squeaks. I’ve tried super cleaning the aluminum and larger irons, but the solder will not stick. I then thought I’d try and plate the aluminum with copper. I actually got the copper to plate into the aluminum, but the mechanical bond was not strong enough and kept breaking away. So my next idea is to machine a new probe end made of brass or steel. Something that I can get solder to stick to. I do not work very fast and had a couple boat fulls of trouble, I think I’m making progress. Hoping the brass probe end will work. Thanks for the help.
Solder won’t stick to the aluminum directly. If you had success with plating it, try just using a small wire to connect the board to the shell instead of trying to solder it direct. That would offer a strain relief and still provide a ground. Another option would be trying a spring to hold pressure on the shell from the board ground.
Radios + Tubes + Scopes + Cars= Nothing better!
Well….. I finally got off dead center and machined a brass end for my Ultra probe. Turned out pretty good. Brass solders a million times better than aluminum. Connected the probe to the amplifier and I do not have that annoying hum and crackle I had with the aluminum end. The probe seems to work. I need to do some more testing. Can anyone suggest a few easy tests for me to check out this system? I suppose I’ll have to go back and look at the films that Paul made, Thanks.
Today, I’m a step closer. I found a bad solder joint in the probes positive lead. Now I’m getting consistent supply voltage to the probe. I thought of trying to set the probe near my RF signal generator to see if the system was working. I had thought I should hear the 400 cps audio on the RF, but nothing. I’m wondering whether or not I blitzed the input FET with all the handling the CB has gotten recently. Still trying.
While working on my Ultra Probe, I noticed that when I touched the amplifier case or metal bat handle switches, the speaker would hum quite a bit. I do not think that is correct. I have my battery outside of the case. I could not get them inside the case, not enough room. So I figured maybe the hum was coming in that way. I also noticed that the negative of the battery is directly connected to the case via the backside of the circuit board. Is this a problem? I want to isolate the circuit entirely from the case and see how that affects the hum.
Well…. after some work, I have the amplifier very quiet and when the signal generator is applied to the input, I get a nice clean signal. Then…. when I connect the probe, there is a boat load of noise and hum. The probe will not pick up the signal generator signal through the air. I can get some of the signal generator when connected directly to the probe circuitry, but is drowned almost completely out by the noise. At least now I believe my problem is entirely in the probe. It’s coming but slowly.
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