Cobra 148 (side mic) intermittent issue

[psycho]

The radio has a pretty much standard peak and tune with a cap mod and variable key. R131 cut and if I remember correctly VR11 was turned up for the ssb output. When working on all 8 cylinders it's an exceptional sounding radio.
Every now and then the radio's output starts dropping on my meter and you can see the SSB output drop from 17 watts to 3 watts. The AM falls off to the point where full key which is normally between 6-7 watts drops to 1/2 watt.
I have enough replacement radios to last me a lifetime but if anyone has a suggestion what might have gone bad, that would be great.
I turn off the radio and the next time I key the radio it's back to normal. Sounds like something is heating up.
I just need some input and if it's easy enough requiring just a part change, I could do it.

 

[ExitThirteen]

Check and see if VR8 and VR9 have been cranked open, if either one of them or both are cranked wide open, that can cause the symptoms you're describing. If nothing else, it's a good starting point. Let us know how you get on.


~Cheers~

 

[unit_399]

Psycho -

If you can hook it up to a supply and monitor the current, see if the current draw drops along with the output. If it does, probably a bad component or solder joint. If current draw remains stable then maybe a poor/intermittent connection after the final and before the antenna. Maybe the antenna connector itself. Either way, it's a place to start. Good luck and 73s.

- 399