Cobra 135 drifting

[tuner]

Hello All,

I picked up a Cobra 135 recently at garage sale. It was well looked after, so I bought it.I came to find the receive was going on it but I was told it sounded real good with the stock mic. I had it looked at by a tech, and was told it looked ok and if I want better receive to pick up a preamplifier for it. So all is good. I was using it last night and I noticed after some good long qso's it really started to drift bad, everyone sounded off freq. and also the coax on the back of the rig was getting hot :blink:... any suggestions?

Thanks in advance,

Tuner

 

[tuner]

Any thoughts guys??

 

[kd-5-bgt]

double check the connection of teh coax to the radio and also check the swr and make sure it is as it should be....most every radio I have had will make some heat after a long ragchew

As far as the drifting....I am not to sure,but my guess is it is related to the heat buildup you were getting...I could be wrong but that is where I would start at

I know there are folks here that know alot more than I do about radios and I am sure they will chime in before to long

 

[office888]

Put it on a frequency counter and find out?

The Dosy counter is a cheap investment.

Sounds like a component might be out of spec or something...

What's your SWR on that frequency?

-Richard-

 

[tuner]

Thanks, but yes my swr is fine, I guess it could just be a heat issue, I'll have to check out some freq counters. I thought maybe someone may have had the same experience with an older rig as this. I have tried it with the cover off to let out the heat. The finals were very very hot, but it seemed to be ok. I may have to rig up a small fan inside and see how that works.

 

[mechanic]

I have an old Cobra 135 base with a switch on the side, gives it a total of 48 channels or more! Nice slider on the Voice Lock to get all the in betweens! Hard to believe that this radio sold for over 400 dollars in 1974!
The over heat problem could be from bad current regulator transistors, this radio has several of these switching types, a poor and out of spec electrolytic capacitor can over work these. This could also cause a frequency shift as stable frequency depends upon stable voltage and current.
This is a pretty old radio and worth saving, I would collect the values of the electrolytic caps and replace them. Especially since the radio may have sat for a long time, bad on the caps!

mechanic

 

[tuner]

Very Good !Thanks Mechanic very much