[Milsurplus] BC-348M

[W7QHO at aol.com]

In a message dated 12/7/06 8:44:49 AM, Military1944 at aol.com writes:


> Second, the set has an odd fault. Its got a mains psu fitted. I see they 
> have grounded the ht negative, so the bais on the VT48 is wrong but thats 
> incidental. On switch on the set comes up, plenty of gain, noise etc. Within a 
> couple of seconds the gain fall off to near quiet. Its just like a cap pulling 
> the ht low but all the tube volt readings are right (within a bit).
>   
> 
> 
Ben,

Sure sounds like something is heating up and shutting the set down.    I 
usually approach problems like this by working back from the output stage by 
stage.   Simply scratching grid leads with a screwdriver
will quickly identify a dead stage in many cases.   Use a signal generator 
operating at appropriate stage frequencies for a more definitive checks, of 
course.

Could be the audio output tube reacting to excessive current draw as someone 
has mentioned. 
Easy to check and correct.   

Good luck.

Dennis D. W7QHO
Glendale, CA
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