[Milsurplus] Another BC-348 question

[wf2u at starband.net]

It's definitely not normal. I encountered one BC-348 which had a crack
through the top rear aluminum stiffening strut (for the lack of anything
better to call it) which enabled the chassis to twist when turning the
tuning knob. This caused severe frequency instability as the main tuning
capacitor base was twisting with the chassis. The problem was fixed by
tapping 4  #8 screw holes in the strut - 2 on each side of the break - and
screwing a piece of aluminum stock to it to hold it together. I have no
idea how that strut broke, as the receiver was otherwise in excellent
shape.
I don't think this kind of failure is very common...

73, Meir WF2U
Landrum, SC


> Ralph,
>  Not normal.
>   Oscillator instability due to mechanical movement can be caused by a
> tube with its internal structure coming undone(probably unlikely but
> similar to microphonic tubes) or one or more air padder condensers
> (APC) on the verge of failure.These air variables have been known to
> fail when the retainer (looks like a nut on the end of the shaft)
> cracks or just gets loose and the cap rotor and stator start to become
> close friends.I've had that happen and it's a bear to get into those RF
> boxes but it is do-able with patience.No coffee!Also I had one -348
> that had a backlash problem in the main tuning cap that I was able to
> improve upon but never got it really fixed.Sold that one at a local
> flea for peanuts(the peanuts were locally grown and delicious!).That
> can cause similar issues with the local oscillator too.
> Good luck,
> Jay KE6PPF
>
> -----Original Message-----
> From: ramcam at magma.ca
> To: milsurplus at mailman.qth.net
> Sent: Thu, 21 Sep 2006 2:52 PM
> Subject: [Milsurplus] Another BC-348 question
>
> Do any list users have experience operating the 348 in an aircraft, on
> cw? Mine
> has some decided instability when the chassis is moved even slightly. I
> imagine
> this could be very distracting to the opr.
>
> Is this normal? Is there a fix? Voltage regulator seems to be working
> fine.
>
> This may have been asnwered in previous lists but I missed it.
>
> Thanks
>
> Ralph Ve3BBM
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