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Post by 321 treeclimber on Sept 19, 2019 9:47:51 GMT -5
Besides bells and whistles what is the power/ audio differences between the 139 and the 2000 ?
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Post by TheStonerGuy on Oct 12, 2019 15:43:11 GMT -5
I think the biggest difference is with the PLL.
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Post by 2600 on Oct 12, 2019 23:41:54 GMT -5
Cobra 139 was a crystal-controlled 23-channel SSB radio, built by Uniden. Used a relay for transmit/receive switching. The contacts in that relay were supported by thermoplastic that would soften if you cranked the transmit too high. The added current draw on transmit would heat the contact points. When the plastic softened, the contacts would sag, causing both transmit and receive circuits to close at the same time. Would short the radio's internal power circuits to ground. Until you replaced the relay. And that's a part that hasn't been made in nearly 40 years.
Cobra 139 XLR was a first-generation 1977 40-channel SSB base. Made by Uniden, the main circuit board was also found in the Robyn SB520D, RatShack TRC457/458 and the original (4-pin mike) President Washington. Has the NEC-made uPD858 PLL chip. Until 1979 it was legal to use a PLL that could cover 399 channels like that one. The FCC took a while to discover how easy it was to break the rule that limits you to 40 channels with this chip. This is the last generation of SSB CB made by Uniden to have a relay for transmit/receive switching. The Omron MX3P relay it uses is in a socket. Makes a worn relay easier to replace. Just one problem. It was discontinued decades ago, so finding a replacement is a catch-as-catch can proposition.
The Cobra 2000 is a post-1979 model with a somewhat-crippled PLL chip made by Fujitsu that can only be tweaked for a handful of extra channels. This was Uniden's first generation of relay-free SSB CB models. The receiver has a separate IF section for AM only, so the selectivity is a little tighter for SSB only, and wider for AM only. It does NOT contain a relay, and uses only the mike to switch from receive to transmit. To make this easier on the designer, they added a second ground pin to the mike plug, making it now five pins. Pin 2 is ground only for the mike-audio signal. Pin 4 is a separate ground for the transmit/receive switching circuits. Only. When the radio first came out this frustrated the snot out of folks who wanted to use their power mikes that had only four wires in the mike cord. Hooking that mike's single ground wire to just one, just the other or to both pins 2 and 4 in the mike would frequently introduce feedback issues in SSB receive or AM transmit or both. A mike with a 6-wire cord usually had the two ground circuits separated properly, like the factory mike.
Power differences? The XLR uses a modulation transformer for AM. This boosts the audio voltage to the final and driver beyond the radio's 13.8-Volt DC supply voltage. The XLR radio can deliver AM peaks of 25 Watts or more if properly tweaked. The later post-1979 radios used a modulator circuit called an "emitter follower" that reduces the peak power on AM just slightly less than the max sideband PEP. Unless, of course someone tweaks it.
Audio differences? The XLR contains a speech compressor chip and a clipper/filter circuit. Some folks like the sound of this, some don't. The post-1979 radios have a simpler AM transmit audio that uses only a modulation limiter and conventional ALC for sideband.
Technology evolves. In the late 1970s a lot of evolution was going on. And for the following 20 or 30 years CB designs kinda stagnated, with few real improvements from decade to decade.
73
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Post by crambone on Oct 13, 2019 9:04:58 GMT -5
Like a walking encyclopedia! Wish I had hundredth of that knowledge in my head.
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Post by 321 treeclimber on Oct 13, 2019 16:13:31 GMT -5
Yeah crambone, me too. Hey 2600, what i am actually asking is...is the 139xlr worth restoring? And is the audio strong enough to warrant using it regularly for skip? And whats your opinion on the 90 ltd? Regarding the xlr,25w peaks are pretty good.
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Post by TheStonerGuy on Oct 14, 2019 11:16:48 GMT -5
Cobra 139 was a crystal-controlled 23-channel SSB radio, built by Uniden. Used a relay for transmit/receive switching. The contacts in that relay were supported by thermoplastic that would soften if you cranked the transmit too high. The added current draw on transmit would heat the contact points. When the plastic softened, the contacts would sag, causing both transmit and receive circuits to close at the same time. Would short the radio's internal power circuits to ground. Until you replaced the relay. And that's a part that hasn't been made in nearly 40 years. Cobra 139 XLR was a first-generation 1977 40-channel SSB base. Made by Uniden, the main circuit board was also found in the Robyn SB520D, RatShack TRC457/458 and the original (4-pin mike) President Washington. Has the NEC-made uPD858 PLL chip. Until 1979 it was legal to use a PLL that could cover 399 channels like that one. The FCC took a while to discover how easy it was to break the rule that limits you to 40 channels with this chip. This is the last generation of SSB CB made by Uniden to have a relay for transmit/receive switching. The Omron MX3P relay it uses is in a socket. Makes a worn relay easier to replace. Just one problem. It was discontinued decades ago, so finding a replacement is a catch-as-catch can proposition. The Cobra 2000 is a post-1979 model with a somewhat-crippled PLL chip made by Fujitsu that can only be tweaked for a handful of extra channels. This was Uniden's first generation of relay-free SSB CB models. The receiver has a separate IF section for AM only, so the selectivity is a little tighter for SSB only, and wider for AM only. It does NOT contain a relay, and uses only the mike to switch from receive to transmit. To make this easier on the designer, they added a second ground pin to the mike plug, making it now five pins. Pin 2 is ground only for the mike-audio signal. Pin 4 is a separate ground for the transmit/receive switching circuits. Only. When the radio first came out this frustrated the snot out of folks who wanted to use their power mikes that had only four wires in the mike cord. Hooking that mike's single ground wire to just one, just the other or to both pins 2 and 4 in the mike would frequently introduce feedback issues in SSB receive or AM transmit or both. A mike with a 6-wire cord usually had the two ground circuits separated properly, like the factory mike. Power differences? The XLR uses a modulation transformer for AM. This boosts the audio voltage to the final and driver beyond the radio's 13.8-Volt DC supply voltage. The XLR radio can deliver AM peaks of 25 Watts or more if properly tweaked. The later post-1979 radios used a modulator circuit called an "emitter follower" that reduces the peak power on AM just slightly less than the max sideband PEP. Unless, of course someone tweaks it. Audio differences? The XLR contains a speech compressor chip and a clipper/filter circuit. Some folks like the sound of this, some don't. The post-1979 radios have a simpler AM transmit audio that uses only a modulation limiter and conventional ALC for sideband. Technology evolves. In the late 1970s a lot of evolution was going on. And for the following 20 or 30 years CB designs kinda stagnated, with few real improvements from decade to decade. 73 I've always thought the 135xlr pre-dated the 139xlr but I've always been curious about the differences. |
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Sandbagger
Administrator/The Boss 
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Post by Sandbagger on Oct 14, 2019 11:53:34 GMT -5
Cobra 139 was a crystal-controlled 23-channel SSB radio, built by Uniden. Used a relay for transmit/receive switching. The contacts in that relay were supported by thermoplastic that would soften if you cranked the transmit too high. The added current draw on transmit would heat the contact points. When the plastic softened, the contacts would sag, causing both transmit and receive circuits to close at the same time. Would short the radio's internal power circuits to ground. Until you replaced the relay. And that's a part that hasn't been made in nearly 40 years. Cobra 139 XLR was a first-generation 1977 40-channel SSB base. Made by Uniden, the main circuit board was also found in the Robyn SB520D, RatShack TRC457/458 and the original (4-pin mike) President Washington. Has the NEC-made uPD858 PLL chip. Until 1979 it was legal to use a PLL that could cover 399 channels like that one. The FCC took a while to discover how easy it was to break the rule that limits you to 40 channels with this chip. This is the last generation of SSB CB made by Uniden to have a relay for transmit/receive switching. The Omron MX3P relay it uses is in a socket. Makes a worn relay easier to replace. Just one problem. It was discontinued decades ago, so finding a replacement is a catch-as-catch can proposition. The Cobra 2000 is a post-1979 model with a somewhat-crippled PLL chip made by Fujitsu that can only be tweaked for a handful of extra channels. This was Uniden's first generation of relay-free SSB CB models. The receiver has a separate IF section for AM only, so the selectivity is a little tighter for SSB only, and wider for AM only. It does NOT contain a relay, and uses only the mike to switch from receive to transmit. To make this easier on the designer, they added a second ground pin to the mike plug, making it now five pins. Pin 2 is ground only for the mike-audio signal. Pin 4 is a separate ground for the transmit/receive switching circuits. Only. When the radio first came out this frustrated the snot out of folks who wanted to use their power mikes that had only four wires in the mike cord. Hooking that mike's single ground wire to just one, just the other or to both pins 2 and 4 in the mike would frequently introduce feedback issues in SSB receive or AM transmit or both. A mike with a 6-wire cord usually had the two ground circuits separated properly, like the factory mike. Power differences? The XLR uses a modulation transformer for AM. This boosts the audio voltage to the final and driver beyond the radio's 13.8-Volt DC supply voltage. The XLR radio can deliver AM peaks of 25 Watts or more if properly tweaked. The later post-1979 radios used a modulator circuit called an "emitter follower" that reduces the peak power on AM just slightly less than the max sideband PEP. Unless, of course someone tweaks it. Audio differences? The XLR contains a speech compressor chip and a clipper/filter circuit. Some folks like the sound of this, some don't. The post-1979 radios have a simpler AM transmit audio that uses only a modulation limiter and conventional ALC for sideband. Technology evolves. In the late 1970s a lot of evolution was going on. And for the following 20 or 30 years CB designs kinda stagnated, with few real improvements from decade to decade. 73 I've always thought the 135xlr pre-dated the 139xlr but I've always been curious about the differences. The 135XLR and the 139XLR were released at similar times in 1977, as the 1st generation of Cobra's 40 channel base radios. The 135 had been Cobra's top of the line radio so when the 40 channel radios came out, they were set to continue that tradition with the 135XLR. But in a couple of years the Cobra 2000 came out and it became the flagship radio for the Cobra line. The 135XLR and the 139XLR were discontinued, and in their place was the 142GTL, which looked like the 139XLR but had the MB8719 PLL chassis with the single conversion receiver. A similar fate awaited the companion mobile version of these models, the 132XLR and 138XLR. The 140GTL became the companion to the 142GTL, and the 148GTL became the companion to the 2000. The 135 and 135XLR (and the 132XLR) were made by Toshiba. Toshiba was considered a "notch up" in design and quality over Uniden (although channel expansion was not as satisfying), which is why Browning, Tram, and Cobra's higher end radios used Toshiba to design and produce certain models. |
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Post by TheStonerGuy on Oct 15, 2019 10:39:34 GMT -5
**The 135 and 135XLR (and the 132XLR) were made by Toshiba. Toshiba was considered a "notch up" in design and quality over Uniden (although channel expansion was not as satisfying), which is why Browning, Tram, and Cobra's higher end radios used Toshiba to design and produce certain models.**
Yes, the 23ch. 135 was made by Toshiba, but the 135xlr has an 858 pll with huge expansion capabilities. I think/thought that version had a Uniden board in it. So following the "Family Tree" that 2600 posted, along with your info, the 135xlr was the top of the line with the 139 being 2nd fiddle? Or was the 135xlr their first top of the line 40ch rig in 1977, which was quickly replaced by the 139xlr that same year?
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Post by 321 treeclimber on Oct 15, 2019 10:49:41 GMT -5
Well, again ,i have 2 139xlrs and just wanted to know if they were as good to restore as a 2000. After deciphering all the tech talk i suppose it is. Especially if capable of 25w pep on am. So these two go on the"keep side of the radio room. Thanks guys
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on Oct 15, 2019 13:49:20 GMT -5
**The 135 and 135XLR (and the 132XLR) were made by Toshiba. Toshiba was considered a "notch up" in design and quality over Uniden (although channel expansion was not as satisfying), which is why Browning, Tram, and Cobra's higher end radios used Toshiba to design and produce certain models.** Yes, the 23ch. 135 was made by Toshiba, but the 135xlr has an 858 pll with huge expansion capabilities. I think/thought that version had a Uniden board in it. So following the "Family Tree" that 2600 posted, along with your info, the 135xlr was the top of the line with the 139 being 2nd fiddle? Or was the 135xlr their first top of the line 40ch rig in 1977, which was quickly replaced by the 139xlr that same year? No, the 135XLR was Toshiba. The 139XLR had the Uniden board with the 858 PLL. |
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Post by sfi355 aka Billy Bob on Oct 15, 2019 15:39:07 GMT -5
Well, again ,i have 2 139xlrs and just wanted to know if they were as good to restore as a 2000. After deciphering all the tech talk i suppose it is. Especially if capable of 25w pep on am. So these two go on the"keep side of the radio room. Thanks guys Yes the Cobra 139XLR is a Keeper. My Radio has all the Factory updates and include the the extra crystal for rejecting side for receiving. I like the way they sound on AM and SSB. And for sure my frequents know when I use this radio. My 139XLR is Bone stock. And I can run it all day long and I am not going to be worried about melting the radio due to have it peaked beyond what the Radio has been designed to do. I have a Icom 706mkiig and a 746 if I need to do the extra channels and more power out. |
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Post by 321 treeclimber on Oct 15, 2019 18:37:50 GMT -5
10-4 335, thats good to know. Ok she's a keeper. 321
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Post by TheStonerGuy on Oct 16, 2019 12:10:22 GMT -5
**The 135 and 135XLR (and the 132XLR) were made by Toshiba. Toshiba was considered a "notch up" in design and quality over Uniden (although channel expansion was not as satisfying), which is why Browning, Tram, and Cobra's higher end radios used Toshiba to design and produce certain models.** Yes, the 23ch. 135 was made by Toshiba, but the 135xlr has an 858 pll with huge expansion capabilities. I think/thought that version had a Uniden board in it. So following the "Family Tree" that 2600 posted, along with your info, the 135xlr was the top of the line with the 139 being 2nd fiddle? Or was the 135xlr their first top of the line 40ch rig in 1977, which was quickly replaced by the 139xlr that same year? No, the 135XLR was Toshiba. The 139XLR had the Uniden board with the 858 PLL. HAH!  I should have known better than to trust my memory... |
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on Oct 16, 2019 16:46:53 GMT -5
No, the 135XLR was Toshiba. The 139XLR had the Uniden board with the 858 PLL. HAH! I should have known better than to trust my memory... One of the casualties of advancing age...... |
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I should have known better than to trust my memory...