Re: [Drakelist] TR7 zener diode noise
Hi Gary, The concern here is RF bypassing. Not to keep RF out of the device, but to keep RF from GETTING out of the device. Which means smaller value ceramic capacitors in addition to any electrolytics used. Diode junctions can produce wideband RF noise that could theoretically impact receiver performance. If you look at the manufacturer data sheets for the 3-terminal devices, they recommend low value bypass caps on both input and output, as physically close to the device as possible. I figger that on the device legs is pretty close... This is the logic behind bypassing the Zeners. There's a repro of the QST note that the OP referenced on the Drake Museum web site. Otherwise, I saw an LM-317 based home built supply years ago that the builder had failed to include the manufacturer's recommended bypass caps in. It was very spikey, going from TX to RX on a 5 watt transciever caused the lamps in the radio to get real bright for a second. Installing one critical cap fixed that. Ever since then, I've been almost evangelical about following the data sheet recommendations for bypass capacitors. 73 -Jim On Sat, 24 Apr 2010 09:22:15 -0400, Garey Barrell wrote: Ron Jim - Maybe I'm missing something, but according to the documentation I have, all of the regulators and Zeners seem to have input and output bypass capacitors. Bypassing multiple pins of a 723 might be counterproductive, actually degrading noise reduction on the output. There is fast, high gain amplification going on in there! This is still one of the best regulators around. Most caps seem to be larger than datasheet values, but based on other Drake gear I assume they are tantalum and so work as well as lower value caps at the higher frequencies. I don't have any numbers, but I suspect that a 1 uF tantalum is just as good (low dissipation and inductance) as a multilayer ceramic. I haven't worked on a lot of TR-7s, usually find that reseating the cards fixes them! :-) Perhaps early units didn't have these caps? Doesn't seem likely. Certainly added caps wouldn't make things worse, with the possible exception of the 723 Christmas tree, but I question the value. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com Jim Shorney wrote: I did do some of the Zener bypassing, but did not measure the results. It didn't make things any worse, I will say that, and I have pretty good MDS numbers on my 7. In addition, I also bypassed the 3-terminal regulator ICs to manufacturer's spec with some surface mount caps on the legs of the IC right next to the body. Again, no measurements, but it didn't hurt, and I've learned over the years that they tell you to put those caps there for some very good reasons. I did find it interesting that all of the TR-7s that I have worked on so far have had the IF gain control maxed out already anyway, in some cases apparently by the good folks at factory service. 73 -Jim On Fri, 23 Apr 2010 17:30:55 -0700 (PDT), Ron wrote: Has anyone actually done and measured the results of bypassing the zener diodes and regulator chips as discussed on QST Feb 1989? The author had anecdotal data only. Was just wondering if there was any instrument measured data floating around out there. Not really planning on doing this, just more of a curiosity. 73, Ron WD8SBB ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime. HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://radiojim.exofire.net http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR7 zener diode noise
Jim - I understand that the concern is high frequency noise getting out of the regulators, but I'm saying that by using tantalum caps they were able to use larger values while still keeping the low inductance of the ceramic style cap. Electrolytic caps inductance and AC impedance go up rapidly with increases in capacitance, due to their internal construction, but tantalums do not, as they are a solid pellet with very low inductance. Just like a ceramic multi-layer cap. Yes, as I said before, there's lotsa wideband gain in those chips, so any transient occurrence, (or Zener noise,) is going to be amplified and maintain a very fast rise-time, i.e., HF (and even low VHF) noise. I don't have a problem with caps on the three terminal regulators, although I believe the tantalums address that concern adequately, but I am concerned about hanging caps on multiple 723 pins. Depending upon just where those pins are in the regulator circuit, adding capacity could seriously impact the ability of the chip to maintain it's terrific low noise performance. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com Jim Shorney wrote: Hi Gary, The concern here is RF bypassing. Not to keep RF out of the device, but to keep RF from GETTING out of the device. Which means smaller value ceramic capacitors in addition to any electrolytics used. Diode junctions can produce wideband RF noise that could theoretically impact receiver performance. If you look at the manufacturer data sheets for the 3-terminal devices, they recommend low value bypass caps on both input and output, as physically close to the device as possible. I figger that on the device legs is pretty close... This is the logic behind bypassing the Zeners. There's a repro of the QST note that the OP referenced on the Drake Museum web site. Otherwise, I saw an LM-317 based home built supply years ago that the builder had failed to include the manufacturer's recommended bypass caps in. It was very spikey, going from TX to RX on a 5 watt transciever caused the lamps in the radio to get real bright for a second. Installing one critical cap fixed that. Ever since then, I've been almost evangelical about following the data sheet recommendations for bypass capacitors. 73 -Jim On Sat, 24 Apr 2010 09:22:15 -0400, Garey Barrell wrote: Ron Jim - Maybe I'm missing something, but according to the documentation I have, all of the regulators and Zeners seem to have input and output bypass capacitors. Bypassing multiple pins of a 723 might be counterproductive, actually degrading noise reduction on the output. There is fast, high gain amplification going on in there! This is still one of the best regulators around. Most caps seem to be larger than datasheet values, but based on other Drake gear I assume they are tantalum and so work as well as lower value caps at the higher frequencies. I don't have any numbers, but I suspect that a 1 uF tantalum is just as good (low dissipation and inductance) as a multilayer ceramic. I haven't worked on a lot of TR-7s, usually find that reseating the cards fixes them! :-) Perhaps early units didn't have these caps? Doesn't seem likely. Certainly added caps wouldn't make things worse, with the possible exception of the 723 Christmas tree, but I question the value. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com Jim Shorney wrote: I did do some of the Zener bypassing, but did not measure the results. It didn't make things any worse, I will say that, and I have pretty good MDS numbers on my 7. In addition, I also bypassed the 3-terminal regulator ICs to manufacturer's spec with some surface mount caps on the legs of the IC right next to the body. Again, no measurements, but it didn't hurt, and I've learned over the years that they tell you to put those caps there for some very good reasons. I did find it interesting that all of the TR-7s that I have worked on so far have had the IF gain control maxed out already anyway, in some cases apparently by the good folks at factory service. 73 -Jim On Fri, 23 Apr 2010 17:30:55 -0700 (PDT), Ron wrote: Has anyone actually done and measured the results of bypassing the zener diodes and regulator chips as discussed on QST Feb 1989? The author had anecdotal data only. Was just wondering if there was any instrument measured data floating around out there. Not really planning on doing this, just more of a curiosity. 73, Ron WD8SBB ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] bulbs T-4XB
Hi folks, both the bulbs at the plate amps rel. output and at the dial stopped working as I turned up the T-4XB. I turned it on after about 1 minute I had turned it off and then the lamps stopped working, I don't know if this could be related to the burning of the lamp, but it happened. Where could I find the right replacement for these bulbs? Looking at the schematic they look like to be ## 47 ## 47 (I am not sure about that) am I correct? What could have been the cause? My T-4XB is so dark now 73, Franco IZ2OOS ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] bulbs T-4XB
Franco - The two bulbs are in series across the 12V filament supply, so if either opens up, they both go out! So one just burned out! The originals are indeed #47 bulbs, and are available from just about any of the usual electronic parts supplier. They are/were the standard bulb in just about every piece of electronic equipment that had bulbs! :-) If you can find them, I would suggest that you replace both bulbs with #755 types. The #47 is a 3000 hour life bulb, while the #755 is a 20,000 hour life bulb, meaning that you most likely will never have to replace them again. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com iz oos wrote: Hi folks, both the bulbs at the plate amps rel. output and at the dial stopped working as I turned up the T-4XB. I turned it on after about 1 minute I had turned it off and then the lamps stopped working, I don't know if this could be related to the burning of the lamp, but it happened. Where could I find the right replacement for these bulbs? Looking at the schematic they look like to be ## 47 ## 47 (I am not sure about that) am I correct? What could have been the cause? My T-4XB is so dark now 73, Franco IZ2OOS ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR7 zener diode noise
My company makes IC voltage regulators. Let me pass along some information. The purpose of the bypass caps for a conventional NPN pass regulator (317, 340, 7800, etc) s as follows. The input cap is to prevent possible oscillations if the lead from the IC to the raw DC filter cap is on the long side. It is just insurance. The output cap is to improve the transient load regulation. IC regs use a feedback loop to steady the output, however, the bandwidth of the loop is finite. The output cap takes over for the loop beyond a certain frequency so as to maintain good transient regulation. A PNP pass regulator (a.k.a. a Low Drop Output regulator) uses the input cap for the same purpose as the NPN types. But it's output cap is not only there for transient load regulation, it is usually mandatory for obtaining loop stability. Because of this special role, you must pay careful attention to it's value and dielectric type as recommended in the datasheet. You generally do not bypass a regulator output to decrease internally generated noise because the output Z is so low that it will fight the cap. Sometimes an IC reg will give you a pin to bypass the internal voltage reference portion of the chip. But this is not common and optional to do anyway. The presence of the input and output caps can help in keeping RF out of the chip's internal circuitry. If you're worried about that use a small value ceramic. Dennis AE6C On Sat, Apr 24, 2010 at 12:26 PM, Jim Shorney jshor...@inebraska.comwrote: Hi Gary, The concern here is RF bypassing. Not to keep RF out of the device, but to keep RF from GETTING out of the device. Which means smaller value ceramic capacitors in addition to any electrolytics used. Diode junctions can produce wideband RF noise that could theoretically impact receiver performance. If you look at the manufacturer data sheets for the 3-terminal devices, they recommend low value bypass caps on both input and output, as physically close to the device as possible. I figger that on the device legs is pretty close... This is the logic behind bypassing the Zeners. There's a repro of the QST note that the OP referenced on the Drake Museum web site. Otherwise, I saw an LM-317 based home built supply years ago that the builder had failed to include the manufacturer's recommended bypass caps in. It was very spikey, going from TX to RX on a 5 watt transciever caused the lamps in the radio to get real bright for a second. Installing one critical cap fixed that. Ever since then, I've been almost evangelical about following the data sheet recommendations for bypass capacitors. 73 -Jim On Sat, 24 Apr 2010 09:22:15 -0400, Garey Barrell wrote: Ron Jim - Maybe I'm missing something, but according to the documentation I have, all of the regulators and Zeners seem to have input and output bypass capacitors. Bypassing multiple pins of a 723 might be counterproductive, actually degrading noise reduction on the output. There is fast, high gain amplification going on in there! This is still one of the best regulators around. Most caps seem to be larger than datasheet values, but based on other Drake gear I assume they are tantalum and so work as well as lower value caps at the higher frequencies. I don't have any numbers, but I suspect that a 1 uF tantalum is just as good (low dissipation and inductance) as a multilayer ceramic. I haven't worked on a lot of TR-7s, usually find that reseating the cards fixes them! :-) Perhaps early units didn't have these caps? Doesn't seem likely. Certainly added caps wouldn't make things worse, with the possible exception of the 723 Christmas tree, but I question the value. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com Jim Shorney wrote: I did do some of the Zener bypassing, but did not measure the results. It didn't make things any worse, I will say that, and I have pretty good MDS numbers on my 7. In addition, I also bypassed the 3-terminal regulator ICs to manufacturer's spec with some surface mount caps on the legs of the IC right next to the body. Again, no measurements, but it didn't hurt, and I've learned over the years that they tell you to put those caps there for some very good reasons. I did find it interesting that all of the TR-7s that I have worked on so far have had the IF gain control maxed out already anyway, in some cases apparently by the good folks at factory service. 73 -Jim On Fri, 23 Apr 2010 17:30:55 -0700 (PDT), Ron wrote: Has anyone actually done and measured the results of bypassing the zener diodes and regulator chips as discussed on QST Feb 1989? The author had anecdotal data only. Was just wondering if there was any instrument measured data floating around out there. Not really planning on doing this, just more of a curiosity. 73, Ron WD8SBB
