Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.net wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, July 29, 2011 3:21 PM Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors Steve - Yes, the PreMixer signal (V8) (BAND minus PTO) is the one that is piped back and forth between the two units. All you have to do is listen to the PTO signal itself on a separate receiver. 0 on the dial = 5.455 MHz, 500 = 4.955. The BFO crystal is 5.595 MHz. The BFO is a tube, V3, which I believe we swapped way back towards the beginning of this odyssey!! I also thought you had put a counter on the PTO, but I guess that's another 'project'. :-) I typically have three or four of these eMail projects going at one time, which is why I like to keep the entire thread together. Makes it easier to go back occasionally just to review just what path got us 'here'! :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: You know, Garey, I've been thinking about the xtal oscillator. It would have to be part that doesn't get bandswitched - which would include THAT transistor. When the T-4X controls the frequency, it sounds great and never jumps frequency. In looking at the schematic, I have been aware that the two solid-state oscillators (PTO and LO for the band) get mixed in V8 (IIRC) and that this combination gets overridden by the output of the T-4X's premixer. Looks like I am going to need a counter to find out. I am loathe to dig into the T-4X because it's working so well and the PTO is much more difficult to remove from it due to the volume of wires in the area. 73, Steve, W1ES Date: Fri, 29 Jul 2011 13:31:12 -0400 From: Garey Barrellk4...@mindspring.com To: Richard Knoppow1oldlens1@ix.netcom.**com 1oldle...@ix.netcom.com Cc: drakelist@zerobeat.net Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors (entirely) Message-ID:4E32EE60.4060209@**mindspring.com4e32ee60.4060...@mindspring.com Content-Type: text/plain; charset=ISO-8859-1; format=flowed Richard - Yes, one wonders..:-) This type of 'dithering' is known in PTOs, but although much less common, a poor crystal oscillator such as the BAND or 2nd MIXER oscillators 'could' present the same way. __**_ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/**mailman/listinfo/drakelisthttp://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
Which is why subbing the Zener is the FIRST thing we check, after making sure the spring is in place!! :-) Is a three-terminal regulator such as a 78LO10 ? a better choice?? 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Dennis Monticelli wrote: I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.net mailto:w1es1...@earthlink.net wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com mailto:k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net mailto:w1es1...@earthlink.net Cc: drakelist@zerobeat.net mailto:drakelist@zerobeat.net Sent: Friday, July 29, 2011 3:21 PM Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors Steve - Yes, the PreMixer signal (V8) (BAND minus PTO) is the one that is piped back and forth between the two units. All you have to do is listen to the PTO signal itself on a separate receiver. 0 on the dial = 5.455 MHz, 500 = 4.955. The BFO crystal is 5.595 MHz. The BFO is a tube, V3, which I believe we swapped way back towards the beginning of this odyssey!! I also thought you had put a counter on the PTO, but I guess that's another 'project'. :-) I typically have three or four of these eMail projects going at one time, which is why I like to keep the entire thread together. Makes it easier to go back occasionally just to review just what path got us 'here'! :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com http://www.k4oah.com/ Steve Wedge wrote: You know, Garey, I've been thinking about the xtal oscillator. It would have to be part that doesn't get bandswitched - which would include THAT transistor. When the T-4X controls the frequency, it sounds great and never jumps frequency. In looking at the schematic, I have been aware that the two solid-state oscillators (PTO and LO for the band) get mixed in V8 (IIRC) and that this combination gets overridden by the output of the T-4X's premixer. Looks like I am going to need a counter to find out. I am loathe to dig into the T-4X because it's working so well and the PTO is much more difficult to remove from it due to the volume of wires in the area. 73, Steve, W1ES Date: Fri, 29 Jul 2011 13:31:12 -0400 From: Garey Barrellk4...@mindspring.com mailto:k4...@mindspring.com To: Richard Knoppow1oldle...@ix.netcom.com mailto:1oldle...@ix.netcom.com
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
The 78L10 is only 39-cents ea. in small quantities through Mouser. I had always assumed that a Zener with current limiting resistor or in the alternative, a Zener with pass transistor would produce a quieter output than a monolithic regulator? So, is it possible that a 78L10 may be more stable as a PTO regulator, but may require more in/out conditioning than a Zener? The Fairchild 78L10 datasheet recommends a 0.33 uF bypass on the input leg, and 0.1 uF bypass on the output. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com To: Dennis Monticelli dennis.montice...@gmail.com Cc: drakelist@zerobeat.net Sent: Saturday, July 30, 2011 2:21 PM Subject: Re: [Drakelist] R-4A PTO: Confirmed it's the PTO. Which is why subbing the Zener is the FIRST thing we check, after making sure the spring is in place!! :-) Is a three-terminal regulator such as a 78LO10 ? a better choice?? 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Dennis Monticelli wrote: I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.net mailto:w1es1...@earthlink.net wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com mailto:k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net mailto:w1es1...@earthlink.net Cc: drakelist@zerobeat.net mailto:drakelist@zerobeat.net Sent: Friday, July 29, 2011 3:21 PM Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors Steve - Yes, the PreMixer signal (V8) (BAND minus PTO) is the one that is piped back and forth between the two units. All you have to do is listen to the PTO signal itself on a separate receiver. 0 on the dial = 5.455 MHz, 500 = 4.955. The BFO crystal is 5.595 MHz. The BFO is a tube, V3, which I believe we swapped way back towards the beginning of this odyssey!! I also thought you had put a counter on the PTO, but I guess that's another 'project'. :-) I typically have three or four of these eMail projects going at one time, which is why I like to keep the entire thread together. Makes it easier to go back occasionally just to review just what path got us 'here'! :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com http://www.k4oah.com/ Steve Wedge wrote: You know, Garey, I've been thinking about the xtal oscillator. It would have to be part that doesn't get bandswitched - which would include THAT transistor. When the T-4X controls the frequency, it sounds great and never jumps frequency
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
I'm interested in Dennis' response to this. Yes, it's a 'more complex' solution, but 'may' be quieter? I don't know if they are more 'stable' or not. I DO know that Zeners ARE noisy, reflected in their use as noise generators for many of the noise sources used for receiver and other testing. This is especially true as they become more 'starved' for current, i.e., the lower the current through them, the noisier they get. Unless Dennis shoots me down on that too!! :-) The Input and Output capacitors on the 3-term regulators are for stability, (oscillation,) rather than signal conditioning. 73, Garey - K4OAH Glen Allen, VA Paul Christensen wrote: The 78L10 is only 39-cents ea. in small quantities through Mouser. I had always assumed that a Zener with current limiting resistor or in the alternative, a Zener with pass transistor would produce a quieter output than a monolithic regulator? So, is it possible that a 78L10 may be more stable as a PTO regulator, but may require more in/out conditioning than a Zener? The Fairchild 78L10 datasheet recommends a 0.33 uF bypass on the input leg, and 0.1 uF bypass on the output. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com To: Dennis Monticelli dennis.montice...@gmail.com Which is why subbing the Zener is the FIRST thing we check, after making sure the spring is in place!! :-) Is a three-terminal regulator such as a 78LO10 ? a better choice?? 73, Garey - K4OAH Glen Allen, VA Dennis Monticelli wrote: I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.net mailto:w1es1...@earthlink.net wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter. Steve Wedge, W1ES/4 - Original Message - From: Garey Barrell k4...@mindspring.com Steve - Yes, the PreMixer signal (V8) (BAND minus PTO) is the one that is piped back and forth between the two units. All you have to do is listen to the PTO signal itself on a separate receiver. 0 on the dial = 5.455 MHz, 500 = 4.955. The BFO crystal is 5.595 MHz. The BFO is a tube, V3, which I believe we swapped way back towards the beginning of this odyssey!! I also thought you had put a counter on the PTO, but I guess that's another 'project'. :-) I typically have three or four of these eMail projects going at one time, which is why I like to keep the entire thread together. Makes it easier to go back occasionally just to review just what path got us 'here'! :-) 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: You know, Garey, I've been thinking about the xtal oscillator. It would have to be part that doesn't get bandswitched - which would include THAT transistor. When the T-4X controls the frequency, it sounds great and never jumps frequency. In looking at the schematic, I have been aware that the two solid-state oscillators (PTO
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
- Original Message - From: Garey Barrell k4...@mindspring.com To: Paul Christensen w...@arrl.net Cc: drakelist@zerobeat.net Sent: Saturday, July 30, 2011 12:04 PM Subject: Re: [Drakelist] R-4A PTO: Confirmed it's the PTO. I'm interested in Dennis' response to this. Yes, it's a 'more complex' solution, but 'may' be quieter? I don't know if they are more 'stable' or not. I DO know that Zeners ARE noisy, reflected in their use as noise generators for many of the noise sources used for receiver and other testing. This is especially true as they become more 'starved' for current, i.e., the lower the current through them, the noisier they get. Unless Dennis shoots me down on that too!! :-) The Input and Output capacitors on the 3-term regulators are for stability, (oscillation,) rather than signal conditioning. 73, Garey - K4OAH Glen Allen, VA Would not a simple RC low pass filter on the output of the Zener prevent the noise from affecting whatever is being fed by it? A filter would cure jumping from a defective Zener but would slow down the jumps so that they were not so abrupt. From my R4B diagram it appears that the by-passing for the emitter of Q-3 and source of Q-2 would smooth out any noise from the Zener quite a bit. I have not combed through this thread but has R-160 been checked? This is the dropping resistor for the Zener. There is also a 6K, 5W resistor, which does not have a designator on the diagram, in series with the +150V line that feeds both oscillator and Q-1. Unlikely but voltage there should be checked with a scope. The Zener could be eliminated by feeding the oscillator and buffer stages from a separate supply. I am also unsure after this very long thread if the Zener was replaced. If the jumping is intermittant and especially if temperature dependant I would be very suspicious that there might be a cracked trace or bad solder joint. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
Interesting point, Dennis. I also remember a noise bridge in the old ARRL handbook that used a zener as the noise source. So what did you use to regulate the voltage: LM340 or similar? Not a bad thought, actually... Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Dennis Monticelli To: Steve Wedge Cc: k4...@mindspring.com ; drakelist@zerobeat.net Sent: Saturday, July 30, 2011 12:31 PM Subject: Re: [Drakelist] R-4A PTO: Confirmed it's the PTO. I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.net wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, July 29, 2011 3:21 PM Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors Steve - Yes, the PreMixer signal (V8) (BAND minus PTO) is the one that is piped back and forth between the two units. All you have to do is listen to the PTO signal itself on a separate receiver. 0 on the dial = 5.455 MHz, 500 = 4.955. The BFO crystal is 5.595 MHz. The BFO is a tube, V3, which I believe we swapped way back towards the beginning of this odyssey!! I also thought you had put a counter on the PTO, but I guess that's another 'project'. :-) I typically have three or four of these eMail projects going at one time, which is why I like to keep the entire thread together. Makes it easier to go back occasionally just to review just what path got us 'here'! :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: You know, Garey, I've been thinking about the xtal oscillator. It would have to be part that doesn't get bandswitched - which would include THAT transistor. When the T-4X controls the frequency, it sounds great and never jumps frequency. In looking at the schematic, I have been aware that the two solid-state oscillators (PTO and LO for the band) get mixed in V8 (IIRC) and that this combination gets overridden by the output of the T-4X's premixer. Looks like I am going to need a counter to find out. I am loathe to dig into the T-4X because it's working so well and the PTO is much more difficult to remove from it due to the volume of wires in the area. 73, Steve, W1ES Date: Fri, 29 Jul 2011 13:31:12 -0400 From: Garey Barrellk4...@mindspring.com To: Richard Knoppow1oldle...@ix.netcom.com Cc: drakelist@zerobeat.net Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
Yes, Garey, when zeners are run at current levels near their knee they do tend to be noisier. Applying this knowledge tends to give better results with a typical zener exhibiting white noise. But should a zener go unstable all bets are off. The 78L series voltage reg is zener based. Depending upon the brand and when it was made it may be better than a discrete zener or not. If you go with a 78L made in say the last 15 years, it will probably be better. The best choice is a voltage regulator that is based upon a bandgap voltage reference. Most linear regulators made in the last 20 years are of the LDO (low drop out) type and these are all bandgap based. The venerable LP2951 comes to mind. It is a low power part with an adjustable output. The popular LM317 is also bandgap based and adjustable, though not LDO. The LM317L low power version comes in a convenient TO-92 transistor package and may be the best physical fit for PTO service. Any of these regs can have their output voltage set with two resistors and will accomodate output caps. You can also buy linear regs that are specified for low noise, but I think that is overkill for our needs. We just need to avoid gross noise issues. Dennis AE6C On Sat, Jul 30, 2011 at 12:04 PM, Garey Barrell k4...@mindspring.comwrote: I'm interested in Dennis' response to this. Yes, it's a 'more complex' solution, but 'may' be quieter? I don't know if they are more 'stable' or not. I DO know that Zeners ARE noisy, reflected in their use as noise generators for many of the noise sources used for receiver and other testing. This is especially true as they become more 'starved' for current, i.e., the lower the current through them, the noisier they get. Unless Dennis shoots me down on that too!! :-) The Input and Output capacitors on the 3-term regulators are for stability, (oscillation,) rather than signal conditioning. 73, Garey - K4OAH Glen Allen, VA Paul Christensen wrote: The 78L10 is only 39-cents ea. in small quantities through Mouser. I had always assumed that a Zener with current limiting resistor or in the alternative, a Zener with pass transistor would produce a quieter output than a monolithic regulator? So, is it possible that a 78L10 may be more stable as a PTO regulator, but may require more in/out conditioning than a Zener? The Fairchild 78L10 datasheet recommends a 0.33 uF bypass on the input leg, and 0.1 uF bypass on the output. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com To: Dennis Monticelli dennis.montice...@gmail.com Which is why subbing the Zener is the FIRST thing we check, after making sure the spring is in place!! :-) Is a three-terminal regulator such as a 78LO10 ? a better choice?? 73, Garey - K4OAH Glen Allen, VA Dennis Monticelli wrote: I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.netmailto: w1es1...@earthlink.net** wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter.
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
The RC on the output of the zener trick works for white noise, but I think the freq jumps would be just as annoying. Dennis AE6C On Sat, Jul 30, 2011 at 2:31 PM, Garey Barrell k4...@mindspring.com wrote: Dennis - Well, I know I want to know more! I've been out of semis so long I'm completely lost. I 'know' a lot of things, (Zeners are noisy,) but didn't know 'why'! An engineering brain is a terrible thing to waste... :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Dennis Monticelli wrote: Hi Ron, Well, what we call a zener these days is actually not a zener (whose breakdown mechanism is actually quantum mechanical tunneling), but rather an avalanche breakdown diode. Electrons get rippped loose by the high electric fields at the PN junction interface, smack into other atoms, kick loose more electrons and pretty soon you've got something akin to a snow avalanche. This is an inherantly noisy process of generating current. When the PN junction is manufactured such that the avalanching occurs at the surface of the semiconductor chip that is bad for stability. Various mobile ions (often from the molding compound itself) migrate to the region of the breakdown under the influence of the attractive electric field. They accumlate there and alter the breakdown characteristic. The point of avalanche then tends to flit from one region to another, each region with a sightly different voltage value. Hence the net zener voltage jumps around in a random fashion. This is in addition to the normal white noise of avalanche. The worst I've ever seen is 500mV and more typically it is a few mV's or ten's of mV, but that is sufficient to shift an LC oscillator. A zener diode made in a sophisticated way can avoid the instability issue entirely but burying the PN junction below the surface of the chip. Probably more than you wanted to know :-) Dennis AE6C On Sat, Jul 30, 2011 at 11:32 AM, Ron wd8...@yahoo.com mailto: wd8...@yahoo.com wrote: Dennis, I would be interested in hearing more about the physics. Not sure if the rest of the list would be. I studied Electronics, and then ended up in computers. Kind of enjoy some good old college lecture series now and then. 73, Ron WD8SBB --- On *Sat, 7/30/11, Dennis Monticelli /dennis.montice...@gmail.com mailto:dennis.monticelli@**gmail.com dennis.montice...@gmail.com/* wrote: From: Dennis Monticelli dennis.montice...@gmail.com mailto: dennis.monticelli@**gmail.com dennis.montice...@gmail.com Subject: Re: [Drakelist] R-4A PTO: Confirmed it's the PTO. To: Steve Wedge w1es1...@earthlink.net mailto: w1es1...@earthlink.net** Cc: drakelist@zerobeat.net mailto:drakelist@zerobeat.net** Date: Saturday, July 30, 2011, 12:31 PM I know from my experience in the semiconductor business that zeners (especially those from a prior era) are notoriously noisy and can become outright unstable to varying degrees. You will not see this with a DVM or other averaging type instrument. You should put a scope on the zener and turn up the gain as high as the scope will go while setting the time base for anywhere from 1 to 100ms/div. Make sure your scope ground connection is right at the zener to keep stray pickup at a minimum. If it is unstable you will see the voltage jumping around in discrete steps. A typical zener will just exhibit white noise which looks like tall grass on the CRT. Both the discrete steps and the white noise will modulate the PTO. The steps manifest as annoying random freq shifts while the white noise just adds to the noise sidebands of the oscillator. The discrete jumps in zener voltage are understood in the physics but unless folks are truly interested in that stuff I won't go into it here. Not to scold the Drake design team (whom I respect) and maybe mostly because I witnessed how the sausage is actually made, but I would NEVER design a zener into a circuit as noise sensitive as an oscillator, mixer or preamp. I designed and built a homebrew antenna noise bridge. Guess what I used as the broadband noise source? Dennis AE6C On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge w1es1...@earthlink.net http://mc/compose?to=**w1es1...@earthlink.nethttp://mc/compose?to=w1es1...@earthlink.net wrote: Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
- Original Message - From: Dennis Monticelli dennis.montice...@gmail.com To: drakelist@zerobeat.net Sent: Saturday, July 30, 2011 2:51 PM Subject: Re: [Drakelist] R-4A PTO: Confirmed it's the PTO. The RC on the output of the zener trick works for white noise, but I think the freq jumps would be just as annoying. Dennis AE6C White noise is what I was refering to. The filter would slow down the rise and fall times of the jumps but not get rid of them, not really useful. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO: Confirmed it's the PTO.
Well, it has been a long, strange trip here. Just finished a little experiment with the PTO and my K3. First of all, the K3 is deaf as a post at 4.9 MHz ;-) but I did get enough of a signal through a scope probe hooked to the PTO output to confirm that it's the PTO that is shifting frequency. Having confirmed that, my next step will be replacing the 3000 pF and the zener - even though I'm fairly convinced the zener is okay (alright - I'll replace the 3000 pF first...). I have a sneaking suspicion that this may be one of the S.A.T. caps. If so, it's going to be interesting since I no longer have a capacitance meter. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, July 29, 2011 3:21 PM Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors Steve - Yes, the PreMixer signal (V8) (BAND minus PTO) is the one that is piped back and forth between the two units. All you have to do is listen to the PTO signal itself on a separate receiver. 0 on the dial = 5.455 MHz, 500 = 4.955. The BFO crystal is 5.595 MHz. The BFO is a tube, V3, which I believe we swapped way back towards the beginning of this odyssey!! I also thought you had put a counter on the PTO, but I guess that's another 'project'. :-) I typically have three or four of these eMail projects going at one time, which is why I like to keep the entire thread together. Makes it easier to go back occasionally just to review just what path got us 'here'! :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: You know, Garey, I've been thinking about the xtal oscillator. It would have to be part that doesn't get bandswitched - which would include THAT transistor. When the T-4X controls the frequency, it sounds great and never jumps frequency. In looking at the schematic, I have been aware that the two solid-state oscillators (PTO and LO for the band) get mixed in V8 (IIRC) and that this combination gets overridden by the output of the T-4X's premixer. Looks like I am going to need a counter to find out. I am loathe to dig into the T-4X because it's working so well and the PTO is much more difficult to remove from it due to the volume of wires in the area. 73, Steve, W1ES Date: Fri, 29 Jul 2011 13:31:12 -0400 From: Garey Barrellk4...@mindspring.com To: Richard Knoppow1oldle...@ix.netcom.com Cc: drakelist@zerobeat.net Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors (entirely) Message-ID:4e32ee60.4060...@mindspring.com Content-Type: text/plain; charset=ISO-8859-1; format=flowed Richard - Yes, one wonders..:-) This type of 'dithering' is known in PTOs, but although much less common, a poor crystal oscillator such as the BAND or 2nd MIXER oscillators 'could' present the same way. ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
