[Milsurplus] [ARC5] Dead BC-348-R

[David Stinson]

P.P.S.
If you have an "active" cap checker like the ZM-11
which can ready leakage current, connect it
(with 57-3 out of the circuit and cap 11-9 either
double-checked or disconnected)
between 1st IF pin 3 and ground.
If the meter shows any leakage current to ground, the
first thing I would suspect would be that IF can wafer.
D.S.

On 8/9/2022 9:07 PM, David Stinson wrote:
> Resistor 57-5 is the Plate B+ resistor for
>   the 1st IF.
> 
> 
> There are two ways to burn-up this resistor.
> Either there is a short somewhere between it
> and the plate of 1st IF, or the resistor failed
> by drifting lower, thus drawing higher and higher
> current until it burns up, like the infamous
> "Chernobyl Resistor" of Johnson Ranger fame.
> 
> The most likely suspect is indeed capacitor 11-9.
> Is your tester passive or does it apply 200+ Volts
> to check it for leakage?
> 
> Put your Ohm meter from the junction of 547-5, 11-9,
> 35-1 and coil 119, and the other lead to ground.
> This should read a fully open circuit. If there is
> leakage to ground, you need to find it.
> 
> If you don't find anything that would leak the B+
> to ground, I would double-check the first IF tube
> to see if it is weak.  If so, the resistor could
> have drifted low, which would raise plate current to
> the point the tube gives up.
> 
> If the tube is good and you don't find a short
> ground, the next suspect would be capacitor 35-1
> shorting and also raising the tube current, enough
> to slowly roast the resistor.
> 
> If you find no leakage to ground as above, replace
> resistor 57-5 and watch it for overheating.
> 
> GL OM ES 73 DE Dave AB5S
> 
> 
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

-- 
This email has been checked for viruses by Avast antivirus software.
www.avast.com