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Cobra 135 XLR sideband issues

FPR1981

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My beloved Cobra 135 XLR base station is a great talking radio, all except the sideband issue. I cannot get the voice lock/clarifier to tune anyone in properly. I can hear the other station talking, but no matter the case, it sounds like jibberish.

Any ideas on what the issue might be? Can AM be fine and SSB have drifted?
 

n9mxq

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They may be on the other side band, or have rigs that "slide" between channels. If your 135 is unmolested it won't keep up with newer rigs that are unfettered by limits.
 

DaveJacobsen

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As pointed out:
USB vs LSB?
Some people tend to hack their radios so the clarifier adusts the transmit frequency too; in which case you could be battling their adjustments & any drift you might have.
My vote would be for the "other sideband" tho.
 

n9mxq

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My bet is your clarifier can't keep up. There are mods, easily found by google to allow it a bit more room. I'm not saying you should, I'm saying you could, if you're so inclined.
 

dispatch235

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I had both the 135 and 135xlr back in the day... the 23 channel 135 the best I remember was a fairly stable radio, however the xlr 40 channel version had lots of problems with stability on ssb. They were fairly notorious for problems... One of the local dealers had mine in the shop and ran it continuously for around a month and pretty much cured its problems by attaching some resistors to the top of the crystals to keep them at a certain operating temperature. Somewhere I still have one of the radios, though I can't remember which one...along with about 20 other various models of Cobras, both 23 and 40 channel radios lol. Every time the local dealer got a different model in stock he had me run one for a while to "get one on the air" and generate some local interest>
 

prcguy

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How old is the radio? As crystals age most drift low in frequency and a 30 year old radio can drift up to a few KHz off frequency. If its drifted further than the clarifier can correct it then you would need to see if there is a way to trim it back on frequency or modify the clarifier to bring it in and also modify it so it works on transmit.
 

FPR1981

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How old is the radio? As crystals age most drift low in frequency and a 30 year old radio can drift up to a few KHz off frequency. If its drifted further than the clarifier can correct it then you would need to see if there is a way to trim it back on frequency or modify the clarifier to bring it in and also modify it so it works on transmit.
Built in 1977. It is the great grandfather to the Cobra 2000.

The 135 XLR was succeeded by the 139 XLR, and then the 142 GTL, before Cobra decked out the 142 with a silver face, fancy meters a frequency counter and extension speaker and called it the Cobra 2000.

The receive on this unit, at least on AM, is far and above any other radio I own. It has a filter designed by Collins, just like the Tram D201A.
 

prcguy

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I used to sell Cobra 135s and 138s and 139s and 2000s in the mid 70s to early 80s. I was curious how old the OPs radio was and its got to be at least 40yrs old and off frequency from natural causes. If its a non XLR 23ch with the Dynascan name then is older.

The 145s had a crystal filter and Collins mostly dealt with mechanical filters. I've never seen a mechanical filter in a Cobra or even a US made filter, its all off shore crystal filters and some with the discreet crystals visible on a small circuit board.

Built in 1977. It is the great grandfather to the Cobra 2000.

The 135 XLR was succeeded by the 139 XLR, and then the 142 GTL, before Cobra decked out the 142 with a silver face, fancy meters a frequency counter and extension speaker and called it the Cobra 2000.

The receive on this unit, at least on AM, is far and above any other radio I own. It has a filter designed by Collins, just like the Tram D201A.
 

iMONITOR

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I'll probably catch a lot of heat saying this buy aren't most of the all time favorite vintage CB's in a similar condition. So old that components are changing if not failing completely making them inferior to most new CB's regardless how great they were in their day?

I know a lot of guys have gone through their rigs or had an experienced radio tech go through them replacing this and that but I think today's CB's are of a better design using more advanced technology and components on advanced circuit board technologies as well.
 

FPR1981

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I'll probably catch a lot of heat saying this buy aren't most of the all time favorite vintage CB's in a similar condition. So old that components are changing if not failing completely making them inferior to most new CB's regardless how great they were in their day?

I know a lot of guys have gone through their rigs or had an experienced radio tech go through them replacing this and that but I think today's CB's are of a better design using more advanced technology and components on advanced circuit board technologies as well.
I think that you can throw accolades to the new stuff and to the old. When you consider that some of these radios are 40 and 50 years old and still in service, it's difficult to find a lot of fault with them.

There has been some modern junk made. Any of those "plastic" Cobras with the push in 5 pin mics, were pretty well junk (the ones with the weather radio function). Midland made some modern crap too.

Depends a lot on pricepoint too.
 

iMONITOR

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The last CB I bought back in the late 70's I recall was a DAK. I got sucked in by it's appearance. Boy was I fooled. It turned out to be a big tin box with a fancy front panel design and not much substance, poorly made. It had what like your average mobile radio board inside. Pathetic.


1614110869037.png1614111459929.png
 

iMONITOR

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A base station is a mobile with a power supply built in.
Amateur HF base transceivers are much different in design and layout. They usually have preamps, better filtering, better dynamic range, better audio, sometimes antenna auto-tuners, larger meters, better displays etc. For what they charged on the DAK I was expecting much more. They wouldn't give the opportunity to even open the cardboard box to peek in the air vents and of course they knew nothing about it so they couldn't answer any questions. I should have just returned it, I had high hopes at the time.
 

wesct

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My bet is your clarifier can't keep up. There are mods, easily found by google to allow it a bit more room. I'm not saying you should, I'm saying you could, if you're so inclined.
I didn't know that the clairfier worked on a clock? WOW! I learn something new everyday
 

wesct

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Amateur HF base transceivers are much different in design and layout. They usually have preamps, better filtering, better dynamic range, better audio, sometimes antenna auto-tuners, larger meters, better displays etc. For what they charged on the DAK I was expecting much more. They wouldn't give the opportunity to even open the cardboard box to peek in the air vents and of course they knew nothing about it so they couldn't answer any questions. I should have just returned it, I had high hopes at the time.
Are we comparing a cobra cb radio to an Icom HF radio?
2 different radios, 2 sifferent services
 

wesct

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I'll probably catch a lot of heat saying this buy aren't most of the all time favorite vintage CB's in a similar condition. So old that components are changing if not failing completely making them inferior to most new CB's regardless how great they were in their day?

I know a lot of guys have gone through their rigs or had an experienced radio tech go through them replacing this and that but I think today's CB's are of a better design using more advanced technology and components on advanced circuit board technologies as well.
The Radio Shack trc 457 and 458 had 90 day wonders (filter caps) in the power supply. When I fixed them, I use computer grade caps for high temps. Problem solved
 
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