[NJARC] Grounding question- Good Lead!

Scott Roberts ng19delta at yahoo.com
Sun Feb 15 23:12:41 EST 2009 

I watched his presentation on the internet while I was teaching Friday night. Didn't get to see all of it, but I am planning to go back and watch it in the archives.

I may still bring the BC-348 to the next clinic- provided USAF doesn't get in the way(which I think it is). Otherwise I keep plugging along. Building the pi filter for the power supply at the moment, then I'll start tapping tubes to see what happens when each is swapped...

Scott



--- On Sun, 2/15/09, John Ruccolo <jr6v6gt at yahoo.com> wrote:

> From: John Ruccolo <jr6v6gt at yahoo.com>
> Subject: Re: [NJARC] Grounding question- Good Lead!
> To: "New Jersey Antique Radio Club" <njarc at mailman.qth.net>
> Date: Sunday, February 15, 2009, 10:07 PM
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Hi Scott,
> 
> Bravo! I was about to suggest that you bring it to the next
> clinic.
> 
> BTW, you missed a very interesting presentation Friday
> night -- actually *two* presentations in one.
> 
> The speaker (Herb Hobler) was a former B-29 navigator who
> participated in the "fire raids" over Tokyo. That
> 348 may have been there as well!
> 
> Regards,
> 
> John
> 
> 
> --- On Sun, 2/15/09, Scott Roberts
> <ng19delta at yahoo.com> wrote:
> 
> > From: Scott Roberts <ng19delta at yahoo.com>
> > Subject: Re: [NJARC] Grounding question- Good Lead!
> > To: "New Jersey Antique Radio Club"
> <njarc at mailman.qth.net>
> > Date: Sunday, February 15, 2009, 4:39 PM
> > Visit our web site - See http://www.njarc.org
> > _______________________________________________
> > Made the switch, and it removed most of the heavy hum-
> > there is still a little bit of hum, but nowhere near
> as
> > overwhelming as it had been- And I finally started
> hearing
> > signals!
> > 
> > I think the remainder of the hum is from my 24 power
> > supply- I have no pi filter on it at the moment, so I
> will
> > put it back into the mix, and see if that fixes the
> rest of
> > the hum.
> > 
> > Scott
> > 
> > 
> > --- On Sun, 2/15/09, Scott Roberts
> > <ng19delta at yahoo.com> wrote:
> > 
> > > From: Scott Roberts <ng19delta at yahoo.com>
> > > Subject: Re: [NJARC] Grounding question- Good
> Lead!
> > > To: "New Jersey Antique Radio Club"
> > <njarc at mailman.qth.net>
> > > Date: Sunday, February 15, 2009, 3:26 PM
> > > Visit our web site - See http://www.njarc.org
> > > _______________________________________________
> > > Got into looking over the radio again this
> afternoon.
> > > Re-examined the big transformer at the back of
> the
> > set,
> > > which houses 101A, 101B, 101C, and found
> something
> > > interesting...
> > > 
> > > One of the regular mods done to the BC-348 model
> is
> > that
> > > the output connection is switched from High
> Impedance
> > > output(early war) to Low Impedance output(later
> war).
> > I had
> > > noticed a wire removed from what is usually the
> high,
> > and
> > > one on the low. Only the low was marked, and I
> really
> > > didn't think about it, as it looked like
> others
> > I've
> > > seen. Well, I took a closer look, and reread the
> > schematic
> > > on the transformer itself, and realized a major
> > difference
> > > from the schematic- instead of being paired in
> the
> > normal
> > > way- three levels, from top to bottom, of two
> > terminals
> > > each, and numbered 1 & 2, 3 & 4, 5 &
> 6, it
> > is
> > > actually setup this way- 1 & 6, 2 & 3, 4
> &
> > 5.
> > > 
> > > This caught my attention- ESPECIALLY when I
> noticed
> > #6,
> > > which is hidden at the lowest right side
> connection,
> > has
> > > "High" marked right above it- where you
> have
> > to
> > > look hard to see it.
> > > 
> > > So- Both High and Low impedance are connected-
> and No.
> > 1 is
> > > not. And guess what is supposed to connect to No.
> 1-
> > The
> > > High Voltage Negative output from the
> dynamotor.(and I
> > > retraced this circuit to confirm it is that) Go
> > Figure-
> > > whoever hacked this radio never noticed the
> output
> > > transformer had a non-standard layout, at least
> not as
> > > regards many models, and did not bother to look
> at the
> > > label: he just followed the general direction to
> move
> > the
> > > top left wire on it to the top right- which is
> correct
> > on
> > > many of these radios, but apparently not all...
> The
> > high
> > > impedance was cross-feeding with the high voltage
> > negative,
> > > with nothing going through the 101B circuit...
> Wonder
> > if
> > > that could be the overwhelming hum...
> > > 
> > > I'm going to go swap the yellow Hi-V neg wire
> back
> > to
> > > its proper position, and see what I get. 
> > > 
> > > Here's hoping- I'll post results.
> > > 
> > > Scott
> > > 
> > > --- On Sun, 2/15/09, Scott Roberts
> > > <ng19delta at yahoo.com> wrote:
> > > 
> > > > From: Scott Roberts
> <ng19delta at yahoo.com>
> > > > Subject: Re: [NJARC] Grounding question-
> Result
> > > > To: "New Jersey Antique Radio
> Club"
> > > <njarc at mailman.qth.net>
> > > > Date: Sunday, February 15, 2009, 3:54 AM
> > > > Visit our web site - See
> http://www.njarc.org
> > > >
> _______________________________________________
> > > > No Change.
> > > > 
> > > > Grumble.
> > > > 
> > > > Scott
> > > > 
> > > > 
> > > > --- On Sun, 2/15/09, Scott Roberts
> > > > <ng19delta at yahoo.com> wrote:
> > > > 
> > > > > From: Scott Roberts
> > <ng19delta at yahoo.com>
> > > > > Subject: [NJARC] Grounding question
> > > > > To: "NJARC Radio Club"
> > > > <njarc at mailman.qth.net>
> > > > > Date: Sunday, February 15, 2009, 1:59
> AM
> > > > > Visit our web site - See
> > http://www.njarc.org
> > > > >
> > _______________________________________________
> > > > > This may sound like a simple question,
> but I
> > do
> > > need
> > > > an
> > > > > answer, although I am pretty sure I
> know it
> > > already...
> > > > > 
> > > > > I am working on my BC-348-P, which I
> got at
> > the
> > > > swapmeet
> > > > > back in August or September at Info
> Age.
> > > > > 
> > > > > I had thought I had corrected all the
> > > modifications
> > > > made to
> > > > > the set, and returned it to original
> shape.
> > > However, I
> > > > still
> > > > > get a loud hum over any and all
> settings. I
> > have
> > > been
> > > > > starting to check voltages and
> resistances
> > at the
> > > > tubes with
> > > > > the I-56-A test set.
> > > > > 
> > > > > Anyway, I just found a change I missed-
> The
> > dial
> > > lamp
> > > > > circuit has been heavily modified- The
> power
> > in
> > > lead
> > > > has
> > > > > been moved from the AVC-Off-MVC switch,
> > front
> > > wafer,
> > > > > position 1, and moved to the 
> VT-86(217,
> > First
> > > I.F.)
> > > > tube
> > > > > socket terminal 7. Continuing through
> the
> > > circuit, the
> > > > > original series arrangement of the
> lamps has
> > been
> > > > changed to
> > > > > parallel, and resistor 503(the flat 60
> ohm
> > dial
> > > lamp
> > > > > resistor) has been bridged across with
> a
> > piece of
> > > bus
> > > > wire.
> > > > > 
> > > > > Could these changes, having been left
> > unnoticed
> > > &
> > > > > intact, be the cause of the overriding
> hum?
> > I am
> > > about
> > > > to
> > > > > restore the circuit, as I would anyway,
> but
> > > wanted to
> > > > see
> > > > > what you guys think.
> > > > > 
> > > > > I'll let you all know the
> > results(hopefully
> > > > positive
> > > > > & hum free) after i complete it and
> test
> > the
> > > unit
> > > > again.
> > > > > 
> > > > > I am still not sure the neon tube in
> the
> > > oscillator
> > > > plate
> > > > > voltage regulator, (id 218, 2J991, or
> 2V991,
> > > JAN-991)
> > > > is
> > > > > operating properly, and wonder if it
> could
> > be
> > > related
> > > > to
> > > > > either, or both issues- the convoluted
> lamp
> > > wiring, or
> > > > the
> > > > > hum...
> > > > > 
> > > > > Thanks!
> > > > > Scott
> > > > >
> > > >
> > >
> >
> ______________________________________________________________
> > > > > NJARC mailing list
> > > > > Home:
> > > http://mailman.qth.net/mailman/listinfo/njarc
> > > > > Help: http://mailman.qth.net/mmfaq.htm
> > > > > Post: mailto:NJARC at mailman.qth.net
> > > > > 
> > > > > This list hosted by: http://www.qsl.net
> > > > > Please help support this email list:
> > > > > http://www.qsl.net/donate.html
> > > >
> > >
> >
> ______________________________________________________________
> > > > NJARC mailing list
> > > > Home:
> > http://mailman.qth.net/mailman/listinfo/njarc
> > > > Help: http://mailman.qth.net/mmfaq.htm
> > > > Post: mailto:NJARC at mailman.qth.net
> > > > 
> > > > This list hosted by: http://www.qsl.net
> > > > Please help support this email list:
> > > > http://www.qsl.net/donate.html
> > >
> >
> ______________________________________________________________
> > > NJARC mailing list
> > > Home:
> http://mailman.qth.net/mailman/listinfo/njarc
> > > Help: http://mailman.qth.net/mmfaq.htm
> > > Post: mailto:NJARC at mailman.qth.net
> > > 
> > > This list hosted by: http://www.qsl.net
> > > Please help support this email list:
> > > http://www.qsl.net/donate.html
> >
> ______________________________________________________________
> > NJARC mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/njarc
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:NJARC at mailman.qth.net
> > 
> > This list hosted by: http://www.qsl.net
> > Please help support this email list:
> > http://www.qsl.net/donate.html
> 
> 
>       
> ______________________________________________________________
> NJARC mailing list
> Home: http://mailman.qth.net/mailman/listinfo/njarc
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:NJARC at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list:
> http://www.qsl.net/donate.html

More information about the NJARC mailing list