What's the difference between Cobra's 138XLR & their 148 GTLl AM SSB CB Radio?

The 138 was a first-generation 40 channel SSB radio made in the late 1970s. IMO the entire XLR series was the best that Cobra ever made. Equipped with the versatile D858 chip which was very easily modifiable for extra frequencies. They were made and sold at time when Cobra was still part of Dynascan corporation and most- but not all- were made in Japan when they were at the peak of their manufacturing prowess. They were very stable on SSB and built to withstand a truck environment- at a time before air ride!

The 148s are good- perhaps the best of the modern-era radios IF you get one that was made in the Philippines or Malaysia. They are also modifiable for extra frequencies but don't convert quite as easily as the 138s. They can be made to slide about 12-15 Kc on the clarifier if you know what you are doing. Since they are a newer radio there are more of them available and pretty much anyone who knows anything at all about radios can work on them.

Avoid the Chinese and Taiwan- made radios. Avoid anything that says 'SoundTracker' on it. Stay away from anything that has a front-mic input. Filipino and Malaysian- made 148s will have a 5-pin mic, all others will have a 4-pin.

I prefer the older radios mostly because they had better build quality. The downside is- they are old, and likely have suffered at the hands of too many golden screwdrivers. There were a lot of ways to modify a 138 and most of them were wrong. BUT- if you find one in good- even stock- condition, pick it up. Send it to someone who knows vintage radios and have them tune it up. It will be worth it.

 

Nothing wrong with the Taiwan manufactured Cobra radios, things went downhill with the radios after Ranger was contracted for manufacture .... Why would anyone need 10-12 Khz of slide on their clarifier?????

 

To get to the 'A' channels of course.

 

Installing a 10KHz drop switch is a better option, the more slide a clarifier has, the more touchy it is to tune. I feel 6 KHz slide is ideal to give access to "1/2 channels".

 

Perhaps, but remember: The 10KHz drop switch is a fairly recent innovation. Back in the day the only way we had to access the 'A' channels was with a slider- unless you were fortunate enough to have a VFO!

Agreed, they did get quite touchy the closer you got to the bottom. That's why there are so many older radios with Vernier dials on them.

 

Seriously??

Fairly recent innovation?

I had it in 1979, on PLL radios like my Royce and later on a cobra 89 xlr, 139xlr and a bunch of other radios. NOT one person I know ever used the clarifier aka slider for this, it was always a switch.

Before that we used a simple switch and a jumped in a crystal.

What is funny is trying to drive, move the knob to an A channel to get it right, switch all the way to me if I wanted to do that.

What radios have verniers on them? I never saw one on a radio.

 

The most common mods for the 148GTL 25 years ago was adding a 6.8 to 8.2 uH choke in series with the OEM Varactor (or a choke in series with an MV1404 Varactor diode to replace the OEM diode), and rewiring for slide to yield just under 1kc up and 16 kc down. Since this made the voicelock 'touchy' for SSB often a mechanical dial gear reduction Vernier was used or less often a multi-turn pot was installed. To get to the 'A' channels one selected the next channel up and slid down 10 kc. This was very common in Phoenix in the 80's, I don't know how it was in your area back in the day. In Phoenix nearly every 148 I saw had this clarifier mod even though the addition of a vernier was less common. Also common was the digital frequency mod instead of a crystal kit due to many discovering the RF impressed on the wires from the crystal kit to the board caused a 'gravelly' sound to the SSB TX signal caused by unwanted frequency modulation.

Having repaired hundreds of 148's in several decades I can say while not many used a vernier enough did that you should have encountered a few if you have done radio repair as a profession over the last 40 years. They were not that rare but possibly the many electronic supply stores and the easy low cost availability of the gear reduction vernier drive in Phoenix made it far more common in Arizona than in other parts of the country. Personally I preferred the voicelock circuit remain unmodified on most radios, above all the HR2510. This is one model where I really despise seeing the RIT circuit hacked.

 

Yeah that may be all true, but it is the long way around the barn. The issue is the A channels, and the comment was made that the use of a switch was a recent innovation when it wasn't.

There are a lot of different mods and kits and people tend to do something that they like which is alright. But I don't see the use of a "slider" more than 10 or 11 kcs as useful nor do I see it useful in a truck which is bouncing around to get A channels. The switch, be it for a PLL-02, 858 or what ever is an easy thing to do - cut the foil, put in a switch and hook up something to pull it down or up.

The verniers I have which are small don't adapt well to CBs, rather look like crap when they are put in the radio. A 10 turn pot is a bit different but still that's too much of a ratio to be useful for a slide of 10kcs or at least I think so.

The thing about crystals is that if they are just thrown in to the radio with stranded wire or wired in a way that the capacitance changes, you get that weird effect of FM but to a point. On sideband there was a couple tricks to fix it, but not many know about it and if I can find my crystal notebook I will post those fixes. It really has to do with people spec'ing the crystal wrong in the kits when they didn't care to begin with. The digital thing wasn't common in 1979 or 80 as you know but kits like beta-com had issues with their kits which is why the crystal specs were wrong and I understood they were changed after the first run - if you remember beta-com and digiscan (I think you would).