[NJARC] Grounding question- Good Lead!

John Ruccolo jr6v6gt at yahoo.com
Sun Feb 15 22:07:12 EST 2009 

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
> > > >
> > >
> >
> ______________________________________________________________
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