[Milsurplus] BC-348M

[David Stinson]

----- Original Message ----- 
From: <Military1944 at aol.com>
Subject: [Milsurplus] BC-348M



> 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).

I don't understand how the voltages on the audio output can
be correct without proper grid bias.
My first guess would be a failure related to the very high current
pulled by the unbiased audio output valve.  Valve cathode going
low-EM with current, thermal intermittant in cathode/screen
resistors, open grid resistor, thermally opening audio transformer
primary, leaky grid coupling cap.

This is an example of how "improving" (ham-hacking)
a military radio ends with disappointment and the
radio being set on the shelf, sold or parted-out.
73 Dave S.