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tektronix 7S14 batteries and time base question
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Miguel Work
Hi,
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I have bought a 7S14 with bad batteries. Hi have replaced batteries for leds, but IR, three in series, 0,9 v for led. https://groups.io/g/TekScopes/album?id=131745 How works delayed time base, is similar to dual time base of other timebases, like 7b52? Regards Miguel -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de GerryR Enviado el: domingo, 3 de noviembre de 2019 20:15 Para: TekScopes@groups.io Asunto: Re: [TekScopes] OT: High Frequency coax?? Copper tubing?? I'm not at all familiar with this type of coax. What is the core material, and what makes it so good at the higher frequencies? GerryR KK4GER
----- Original Message -----
From: "Dennis Tillman W7PF" <dennis@ridesoft.com> To: <TekScopes@groups.io> Sent: Sunday, November 03, 2019 1:46 PM Subject: Re: [TekScopes] OT: High Frequency coax?? Copper tubing?? These two sizes of Semi-Rigid Copper Coax cable are very common: RG-402 which is 3.58mm OD (0.141" OD) RG-405 which is 2.20mm OD (0.0865" OD) Working with it is very different compared to typical coax we are all used to. Tools to cut it properly and to bend it properly are expensive. Using common tools to cut it like a pipe cutter, and to bend it like an inexpensive bending jig, will almost certainly affect the high frequency performance of whatever you make. Dennis Tillman W7PF -----Original Message----- From: Reginald Beardsley Sent: Sunday, November 03, 2019 9:01 AM Here's a representative link for the information you're looking for: http://www.sumlocable.com/sub_product/rg401-rg402rg405-semi-rigid-43.html There's lots more. This was simply the first one google tossed up. It is great stuff provided you don't want to bend it more than once. Though rebending used cables is OK. The solder filled braid "RG402" has become my standard cable for anything above 1 GHz. I've made a couple of H field probes from a used piece of high grade stuff. Connector quality on Chinese ebay jumpers is rather variable. I've been documenting my efforts in this thread: https://www.eevblog.com/forum/rf-microwave/testing-rf-connectors-and-cables/ I will be supplementing the TDR results with 8753B/85046A testing soon now that I have an APC-7 cal kit and adapters. Have Fun! Reg -- Dennis Tillman W7PF TekScopes Moderator
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Hi Miguel,
You hijacked another thread (OT: High Frequency coax?? Copper tubing??) Start a new thread if you want to start a new subject. It's called "New Topic" in the web interface. For an explanation of the workings of the 7S14, go here: http://w140.com/tekwiki/wiki/7S14 and download the Service Manual. See the link below the picture at the right side of the Tekwiki page. Did you verify the total voltage delivered by your leds? It's best to stay in the range of the original batteries. Raymond
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Hi Miguel,
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Before I get to the 7S14 I have to ask why you chose Infrared LEDs? They are very inefficient so I am not surprised you needed 3 of them. The 7S14 (and 5S14) is a plugin that has many unmatched capabilities: 1) The way it works is almost exactly the same as any other Tektronix dual trace, dual time base plugin. If you already know how a delayed time base works in a regular Tek scope you will quickly understand how to use the delayed time base of the 7S14. 2) It is the only delayed sampling time base Tek made (except for the 5S14 which is identical to the 7S14) 3) The 5S14 extends the 2MHz bandwidth of even the slowest 5000 series scopes to 1GHz. The 7S14 does the same for even the slowest (7313) 7000 series scopes by extending any mainframe speed to 1GHz. You could not buy a 1GHz dual trace dual time base instrument for less than by combining these two plugins in these two scope series. 4) The 7S14 is the least expensive way to get dual trace capability. The only way to get the equivalent with the 7S11 plugin would be to use two 7S11s side by side like this: 7S11 / 7S11 / 7T11. That would also require two sampling heads. This is a very expensive way to get dual trace capability by comparison. There is no way beside the 5S14 to get dual trace sampling on the 5000 series scopes. There is no equivalent to the 7S11 and 7T11 in the 5000 series. 5) The 7S14 / 5S14 can do X/Y sampling up to 1GHz. There is no other way to do that. In fact the horizontal amplifier of every 7000 mainframe except one is only capable of a few MHz. That limits the capability of any 7000 scope (except the 7104) to displaying only low frequency X/Y traces. The astounding 7104 is capable of displaying X/Y waveforms to over 1 GHz since the 3dB bandwidth of the internal 7104 horizontal amplifier is >400MHz. 6) The triggering on the 7S14 and 5S14 is outstanding. It works exactly like you would expect. It takes no more than a few seconds to get it to trigger where you want on a waveform. By comparison the 7S11 / 7T11 takes typically 30 minutes of fiddling before you get it to trigger somewhere on a waveform. 15 minutes after that you may actually be able to get it to trigger where you want on the waveform, or at least nearby. The only things I can say that are positive about the 7S11 / 7T11 pair are 1) It can, at least in theory, sample and display waveforms up to 14GHz. This will require spending a lot of time fiddling with trigger levels before you are able to actually see a waveform that is that fast. 2) Its system rise time is 30pSec. That was the fastest rise time there was for 15 years after the 7S11 / 7T11 was introduced. By now you can see why there is simply no comparison of the 7S14 to any other sampling plugin made by Tek. Dennis Tillman W7PF
-----Original Message-----
From: Miguel Work Sent: Sunday, November 03, 2019 11:56 AM Subject: [TekScopes] tektronix 7S14 batteries and time base question Hi, I have bought a 7S14 with bad batteries. Hi have replaced batteries for leds, but IR, three in series, 0,9 v for led. https://groups.io/g/TekScopes/album?id=131745 How works delayed time base, is similar to dual time base of other timebases, like 7b52? Regards Miguel -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de GerryR Enviado el: domingo, 3 de noviembre de 2019 20:15 Para: TekScopes@groups.io Asunto: Re: [TekScopes] OT: High Frequency coax?? Copper tubing?? I'm not at all familiar with this type of coax. What is the core material, and what makes it so good at the higher frequencies? GerryR KK4GER ----- Original Message ----- From: "Dennis Tillman W7PF" <dennis@ridesoft.com> To: <TekScopes@groups.io> Sent: Sunday, November 03, 2019 1:46 PM Subject: Re: [TekScopes] OT: High Frequency coax?? Copper tubing?? These two sizes of Semi-Rigid Copper Coax cable are very common: RG-402 which is 3.58mm OD (0.141" OD) RG-405 which is 2.20mm OD (0.0865" OD) Working with it is very different compared to typical coax we are all used to. Tools to cut it properly and to bend it properly are expensive. Using common tools to cut it like a pipe cutter, and to bend it like an inexpensive bending jig, will almost certainly affect the high frequency performance of whatever you make. Dennis Tillman W7PF -----Original Message----- From: Reginald Beardsley Sent: Sunday, November 03, 2019 9:01 AM Here's a representative link for the information you're looking for: http://www.sumlocable.com/sub_product/rg401-rg402rg405-semi-rigid-43.html There's lots more. This was simply the first one google tossed up. It is great stuff provided you don't want to bend it more than once. Though rebending used cables is OK. The solder filled braid "RG402" has become my standard cable for anything above 1 GHz. I've made a couple of H field probes from a used piece of high grade stuff. Connector quality on Chinese ebay jumpers is rather variable. I've been documenting my efforts in this thread: https://www.eevblog.com/forum/rf-microwave/testing-rf-connectors-and-cables/ I will be supplementing the TDR results with 8753B/85046A testing soon now that I have an APC-7 cal kit and adapters. Have Fun! Reg -- Dennis Tillman W7PF TekScopes Moderator -- Dennis Tillman W7PF TekScopes Moderator
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On Mon, Nov 4, 2019 at 12:35 AM, Dennis Tillman W7PF wrote:
Hi Dennis, Thanks for the info on the 7S14 vs. 7T11/S11. Two questions: 1. Is your >400 MHz horizontal BW for the 7104 a number from general experience? The spec is 350 MHz but of course, Tek always exceeded its specs... 2. Isn't Option 2 (phase correction) a virtual necessity for correct phase interpretation of XY displays at higher frequencies? For this also I'm making an appeal on your practical experience with this 'scope. Raymond
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Alberto, IZ2EWV
Hi Miguel,
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I think that you could find help here: http://w140.com/tekwiki/wiki/7S14_repair 73 de Alberto, IZ2EWV Il giorno domenica 3 novembre 2019, Miguel Work <harrimansat@hotmail.com> ha scritto:
Hi,
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Miguel Work
Hi Denis, thanks for your answer,
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Because I need 1.35v x2, with 3+1 leds and 10 mA I have exactly these voltage, each led gives 0.9V, with a 1Mohm load. I´m using SFH 487 leds Regards Miguel -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Dennis Tillman W7PF Enviado el: lunes, 4 de noviembre de 2019 0:36 Para: TekScopes@groups.io Asunto: Re: [TekScopes] tektronix 7S14 batteries and time base question Hi Miguel, Before I get to the 7S14 I have to ask why you chose Infrared LEDs? They are very inefficient so I am not surprised you needed 3 of them. The 7S14 (and 5S14) is a plugin that has many unmatched capabilities: 1) The way it works is almost exactly the same as any other Tektronix dual trace, dual time base plugin. If you already know how a delayed time base works in a regular Tek scope you will quickly understand how to use the delayed time base of the 7S14. 2) It is the only delayed sampling time base Tek made (except for the 5S14 which is identical to the 7S14) 3) The 5S14 extends the 2MHz bandwidth of even the slowest 5000 series scopes to 1GHz. The 7S14 does the same for even the slowest (7313) 7000 series scopes by extending any mainframe speed to 1GHz. You could not buy a 1GHz dual trace dual time base instrument for less than by combining these two plugins in these two scope series. 4) The 7S14 is the least expensive way to get dual trace capability. The only way to get the equivalent with the 7S11 plugin would be to use two 7S11s side by side like this: 7S11 / 7S11 / 7T11. That would also require two sampling heads. This is a very expensive way to get dual trace capability by comparison. There is no way beside the 5S14 to get dual trace sampling on the 5000 series scopes. There is no equivalent to the 7S11 and 7T11 in the 5000 series. 5) The 7S14 / 5S14 can do X/Y sampling up to 1GHz. There is no other way to do that. In fact the horizontal amplifier of every 7000 mainframe except one is only capable of a few MHz. That limits the capability of any 7000 scope (except the 7104) to displaying only low frequency X/Y traces. The astounding 7104 is capable of displaying X/Y waveforms to over 1 GHz since the 3dB bandwidth of the internal 7104 horizontal amplifier is >400MHz. 6) The triggering on the 7S14 and 5S14 is outstanding. It works exactly like you would expect. It takes no more than a few seconds to get it to trigger where you want on a waveform. By comparison the 7S11 / 7T11 takes typically 30 minutes of fiddling before you get it to trigger somewhere on a waveform. 15 minutes after that you may actually be able to get it to trigger where you want on the waveform, or at least nearby. The only things I can say that are positive about the 7S11 / 7T11 pair are 1) It can, at least in theory, sample and display waveforms up to 14GHz. This will require spending a lot of time fiddling with trigger levels before you are able to actually see a waveform that is that fast. 2) Its system rise time is 30pSec. That was the fastest rise time there was for 15 years after the 7S11 / 7T11 was introduced. By now you can see why there is simply no comparison of the 7S14 to any other sampling plugin made by Tek. Dennis Tillman W7PF
-----Original Message-----
From: Miguel Work Sent: Sunday, November 03, 2019 11:56 AM Subject: [TekScopes] tektronix 7S14 batteries and time base question Hi, I have bought a 7S14 with bad batteries. Hi have replaced batteries for leds, but IR, three in series, 0,9 v for led. https://groups.io/g/TekScopes/album?id=131745 How works delayed time base, is similar to dual time base of other timebases, like 7b52? Regards Miguel -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de GerryR Enviado el: domingo, 3 de noviembre de 2019 20:15 Para: TekScopes@groups.io Asunto: Re: [TekScopes] OT: High Frequency coax?? Copper tubing?? I'm not at all familiar with this type of coax. What is the core material, and what makes it so good at the higher frequencies? GerryR KK4GER ----- Original Message ----- From: "Dennis Tillman W7PF" <dennis@ridesoft.com> To: <TekScopes@groups.io> Sent: Sunday, November 03, 2019 1:46 PM Subject: Re: [TekScopes] OT: High Frequency coax?? Copper tubing?? These two sizes of Semi-Rigid Copper Coax cable are very common: RG-402 which is 3.58mm OD (0.141" OD) RG-405 which is 2.20mm OD (0.0865" OD) Working with it is very different compared to typical coax we are all used to. Tools to cut it properly and to bend it properly are expensive. Using common tools to cut it like a pipe cutter, and to bend it like an inexpensive bending jig, will almost certainly affect the high frequency performance of whatever you make. Dennis Tillman W7PF -----Original Message----- From: Reginald Beardsley Sent: Sunday, November 03, 2019 9:01 AM Here's a representative link for the information you're looking for: http://www.sumlocable.com/sub_product/rg401-rg402rg405-semi-rigid-43.html There's lots more. This was simply the first one google tossed up. It is great stuff provided you don't want to bend it more than once. Though rebending used cables is OK. The solder filled braid "RG402" has become my standard cable for anything above 1 GHz. I've made a couple of H field probes from a used piece of high grade stuff. Connector quality on Chinese ebay jumpers is rather variable. I've been documenting my efforts in this thread: https://www.eevblog.com/forum/rf-microwave/testing-rf-connectors-and-cables/ I will be supplementing the TDR results with 8753B/85046A testing soon now that I have an APC-7 cal kit and adapters. Have Fun! Reg -- Dennis Tillman W7PF TekScopes Moderator -- Dennis Tillman W7PF TekScopes Moderator
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Miguel Work
Thanks Ablerto,
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U145B, MC1448, was bad, replaced for a 4558 dual op now I can regulate delayed time base position Thanks Regards Miguel -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Alberto, IZ2EWV Enviado el: lunes, 4 de noviembre de 2019 7:58 Para: TekScopes@groups.io Asunto: Re: [TekScopes] tektronix 7S14 batteries and time base question Hi Miguel, I think that you could find help here: http://w140.com/tekwiki/wiki/7S14_repair 73 de Alberto, IZ2EWV
Il giorno domenica 3 novembre 2019, Miguel Work <harrimansat@hotmail.com> ha scritto:
Hi,
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Hi Raymond,
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You're a stickler for the specs. You are correct on both accounts but I believe I was able to work around them: 1) The bandwidth is 350MHz but I use a 7A29 in the horizontal slot which probably accounted for my impression that I got greater than 350MHz. 2) Option 2 (phase compensation), which is not a common option, would be necessary for some applications but I did not need it. I use a 7A29 Option 4 Variable Delay plugin to adjust phase if I need to. I have owned three ARGOSystems AS210 Rubidium (Rb) Standards for over 10 years. They are very interesting systems. They were designed to fit into a TM515 Traveler Main Frame so they would be portable and could be used in the field whenever it was necessary to make precise measurements based on an accurate frequency standard. The TM515 is gutted then the Rb oscillator is installed along side a new smaller power than the original TM515 supply. A fan is added to keep everything cool. The rear interface board was replaced with a custom one. All of the plugins phase lock to the Rb oscillator. The one that is of particular importance to this story is the AS-210-03 Frequency Generator which generates several fixed reference frequencies (1MHz, 10MHz, 50MHz, 100MHz, 200MHz, ... 500MHz). The Achilles heel of the system became apparent when I asked John Miles to evaluate the Rb Oscillator - the heart of the system. Its Phase Noise performance was poor. In other words it has a lot of phase noise. One day I decided to see if it would be possible to view a 100MHz Lissajous circle from the AS-210-03 Frequency Generator on a 7000 scope in X/Y mode. I first tried this on a 7603. I was puzzled when it didn't work. Next I tried it on a 7704A which was a 200MHz scope so I expected it would work. The result was the same. Scratching my head I tried it on a 7854, a 400MHz scope. The results were no better. There was no horizontal deflection. That is when I discovered every Tek 7000 scope (but one) has a very limited horizontal capability. I always assumed the horizontal signal chain had to be as fast as the vertical but that was because I never thought about it. The horizontal bandwidth / sensitivity is lower due to the deflection plates being further forward from the vertical deflection plates. Checking the specs of several scopes confirmed the horizontal amplifier was not fast except for the 7104's 350MHz Horizontal BW. Now I had a way to do this little experiment. First I adjusted all three of my ARGOSystems AS210s to the output of my Thunderbolt based GPS Frequency Receiver (which I own thanks to John Miles). Once each ARGOSystems AS210 was fine tuned to match the GPS reference I disconnected it. The AS210s were each running on their own at this point but they are stable to 10^-9. Next I fed the output of the AS-210-03 Frequency Generator in the FIRST ARGOSystems AS210 to the 7A29 vertical amplifier of the 7104. Then I fed the AS210-03 Frequency Generator in the SECOND ARGOSystems AS210 to the 7A29 horizontal amplifier of the 7104. Both ARGOSystems were completely independent. I started out at 100MHz on both AS210-03s and got a perfect Lissajous circle (with some phase noise which added fuzz to it). As I increased the frequency to 200MHz, then 300MHz, and 400MHz the circle got progressively fuzzier due to the phase noise but it was still a circle. At 500MHz the horizontal gain began to drop a noticeable amount which was easy to fix by increasing the gain of the 7A29 to 200mV/Div in each axis. The phase noise fuzz was now the dominant thing on the screen. It almost obscured the circle. But the circle was still there and I could see the phase slowly starting to shift between the two Rb standards. Each full turn of the circle represented a phase shift of 360 degrees. This was occurring every 2 to 5 seconds. From that I concluded the Rb standards were within ~1/2Hz of each other on average at 500MHz. That is on the order of 500 x 10^6 / 0.5 = 10 ^9 or 1 part in a billion over a 5 second period. I didn't stop there. I put two 7D14 Frequency Counter plugins into the 7104 to measure the 500MHz frequency going to each 7A29. The first time I did this I was very disappointed to see the 7D14 crystal time base stability was only good to the first 6 on-screen digits but it displays a full 8 digits. I was not going to accept that. I found 8 OCXOVT-BV5 10MHz OCXOs for $10 each on eBay about 6 years ago that were 100X better than the original 7D14 crystal. Since the same crystal is used in the 7D11, 7D14, and 7D15 I designed a simple drop-in replacement PC Board and built 8 of them as replacements in my plugins. I put a detailed description of what this little side project was all about up on TekScopes. It is in the files section. It is called "Tek 7D11 & 7D14 & 7D15 OCXO.pdf" and it is at: https://groups.io/g/TekScopes/files/Tek%207D11%20&%207D14%20&%207D15%20OCXO.pdf Dennis Tillman W7PF
-----Original Message-----
From: Raymond Domp Frank Sent: Sunday, November 03, 2019 4:13 PM On Mon, Nov 4, 2019 at 12:35 AM, Dennis Tillman W7PF wrote: The astounding 7104 is capable of displaying X/Y waveforms to over 1Hi Dennis, Thanks for the info on the 7S14 vs. 7T11/S11. Two questions: 1. Is your >400 MHz horizontal BW for the 7104 a number from general experience? The spec is 350 MHz but of course, Tek always exceeded its specs... 2. Isn't Option 2 (phase correction) a virtual necessity for correct phase interpretation of XY displays at higher frequencies? For this also I'm making an appeal on your practical experience with this 'scope. Raymond -- Dennis Tillman W7PF TekScopes Moderator
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On Wed, Nov 6, 2019 at 12:08 AM, Dennis Tillman W7PF wrote:
Hi Dennis, Thanks for that information. I guess I should have made the following disclosure: About a year ago, I acquired a 7104 with option 2. My first 7104 didn't have that. This 7104 with 2 x 7A29 (one has option 4) and a 7B15 (no 7B10) is in an absolutely pristine condition: The painted parts of the case are still silky dull all over, not the local leathery look that develops from touching, even the bent and cut edges are still covered in paint, no Al shining through. It definitely has *not* been repainted, as can be seen when inspecting the inside of the panels and it matches the overall condition. No dust, it has obviously been stored in the dark (no yellowing of buttons, no paint abrasion of printed texts on buttons). Very late series. And of course, the MCP CRT has virtually no traces of use. The inside of the instrument looks absolutely new. Obviously, a like-new service manual was included. The instrument was "used" in a university-affiliated lab, where it was kept in a closet, only to be brought out when necessary for some job and returned immediately afterward. I guess they realized the cost and vulnerability of the toy. The only things missing were the original cardboard box and packaging materials.... I'm keeping it in a dark place that's actually more like a vault... Re. the OCXOVT-BV5 ovenized oscillator: I also bought a few (4) some years ago and used one as the time base in my 2252 portable 'scope. In that 'scope the PLL circuits had failed. A simple phase detector built with a 74LS86 EXOR gate as an external replacement sorted that out. Raymond
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Miguel Work
Best efficiency is obtained with long wavelength LEDs
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Chuck Harris
Hi Miguel,
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Why is that? I would think that the shorter wavelengths with their higher photon energy would be better. -Chuck Harris Miguel Work wrote:
Best efficiency is obtained with long wavelength LEDs
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Leon Robinson
Maybe better responsiveness at longer wavelengths?
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Leon Robinson K5JLR Political Correctness is a Political Disease. Politicians and Diapers should be changed often and for the same reasons.
On Sunday, December 22, 2019, 10:08:56 PM CST, Chuck Harris <cfharris@erols.com> wrote:
Hi Miguel, Why is that? I would think that the shorter wavelengths with their higher photon energy would be better. -Chuck Harris Miguel Work wrote: Best efficiency is obtained with long wavelength LEDs
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Chuck Harris
Hi Leon,
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If I have been following correctly (always suspect), aren't we using an LED illuminated by another LED to behave as a photo diode, and produce the bias voltage for the switch? If so, I would think that an LED of the same color as the "bias" LED would work best, as they are both set up to deal with the same physics of electron levels, and photon energy. I haven't given a lot of thought to the physics involved, maybe they are different mechanisms? -Chuck Harris Leon Robinson wrote:
Maybe better responsiveness at longer wavelengths?
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John Griessen
On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren'tOne thing for sure from back when I worked with near IR LEDs and laser diodes in a narrow beam system is that what absorbs IR or reflects or not is not obvious from our visible light experience... So, the efficiency could be because the incoming IR light "gets in" instead of reflecting. They are both designed only to output, yet one is being used to receive... Longer IR tends to go through more things that look black to us, and probably go right through the plastic of LED lamps without much refraction so angle and placement can be whatever.
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Chuck Harris
Hi John,
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That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers. When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using. I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough. Or, maybe the mechanism is not reciprocal? -Chuck John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:If I have been following correctly (always suspect), aren'tOne thing for sure from back when I worked with near IR LEDs and laser diodes
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Miguel Work
For my experience, semiconductors are more sensible for IR wavelengths, is not casual that optocouplers works with IR.
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https://www.facebook.com/search/top/?q=optical%20communication%20using%20leds%20alone&epa=SEARCH_BOX CCD for exemple is more sensible for red light. Regards Miguel -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Chuck Harris Enviado el: lunes, 23 de diciembre de 2019 16:15 Para: TekScopes@groups.io Asunto: Re: [TekScopes] tektronix 7S14 batteries and time base question Hi John, That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers. When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using. I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough. Or, maybe the mechanism is not reciprocal? -Chuck John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:If I have been following correctly (always suspect), aren't we usingOne thing for sure from back when I worked with near IR LEDs and laser
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Carl Hallberg
Hi Chuck,
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I used 8 Red, 5mm size, clear plastic, 15,000 mcd, dome type LEDs glued together in pairs after grinding the domes flat. Also used heat shrink over each pair. This produced approximately 1.4V output while supplying 20 mA to the driver LED. I later added a 15uF TANT (might be too big, but had lots of them) to the output LED per Ed Breya. This worked ok. I later experimented with flat top (wide angle) LEDs with white driver (20,000 mcd) to red output. Not too much difference. I first use duco cement, but found 'Crazy Glue' was a better choice. Dennis Tillman now has this 7S14 and was happy it worked after he replace the 'time' knob. I did take picture before the caps and after. Carl Hallberg (W9CJH)
On Monday, December 23, 2019, 9:15:07 AM CST, Chuck Harris <cfharris@erols.com> wrote:
Hi John, That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers. When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using. I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough. Or, maybe the mechanism is not reciprocal? -Chuck John Griessen wrote: On 12/22/19 11:30 PM, Chuck Harris wrote:If I have been following correctly (always suspect), aren'tOne thing for sure from back when I worked with near IR LEDs and laser diodes
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Chuck Harris
Back in the day, IR LED's were the first developed, and
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always made more power, more efficiently than any other variety. I suspect that the same is still true, though blue probably gives them a run for the money... -Chuck Harris Miguel Work wrote:
For my experience, semiconductors are more sensible for IR wavelengths, is not casual that optocouplers works with IR.
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Chuck Harris
Hi Carl,
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I did this experiment long, long ago, so any modern LED is very much brighter than those I used. I will give it a try with more modern LEDs. -Chuck Harris Carl Hallberg via Groups.Io wrote:
Hi Chuck,
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Hi Chuck and John
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I was surprised that several people ground the LED ends flat and glued them together. This seems counter intuitive to me for several reasons. These are the reasons I think that grinding down the LED ends is not a good idea. I would appreciate it if you could explain the flaws in my thinking. 1) The polished surface of the LED lets the most light out. Wouldn’t a ground down (rough) surface scatter and block a portion of the emitted light. 2) The LED's dome shape focuses the light into a fairly narrow angle which increases the likelihood that the majority of the emitted light can be aimed right at the die of the LED that will convert the light to electricity. 3) Crazy Glue may appear clear to humans but what are its optical absorption characteristics? Does it absorb any of the wavelengths generated by the LED emitter? On the other hand I think there are advantages to grinding the ends flat: 1) The ground end combination takes up a fraction of the volume of two unground LEDs. 2) Mating the two LEDs flat against each makes it easier to align them to each other. It seems to me that the greatest conversion efficiency will come when you can place a bare emitting LED die on top of the die of the receiving LED. At that point every emitted photon can kick out an electron in the receiving PN junction. IR light is another issue I'm confused about. I think I must have misunderstood but it sounded like some people think IR LEDs would make a good choice for emitters. Wouldn't just the opposite be true since a photon's energy, E, is proportional to its frequency, v, as in E = hv. Do IR LEDs emit more photons (greater brightness) and that is why they are a good choice? If so does the same thing apply for the receiving LED - which would have a high conversion efficiency resulting in the largest number of electrons being produced? Dennis Tillman W7PF
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From: Chuck Harris Sent: Monday, December 23, 2019 7:15 AM Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question Hi John, That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers. When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using. I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough. Or, maybe the mechanism is not reciprocal? -Chuck John Griessen wrote: On 12/22/19 11:30 PM, Chuck Harris wrote:If I have been following correctly (always suspect), aren't we usingOne thing for sure from back when I worked with near IR LEDs and laser -- Dennis Tillman W7PF TekScopes Moderator
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