[Milsurplus] Couple things about the ARC cap in the ebay homebrew

[W0KPX]

It has been a few years since I opened up the B&W 2Q4 that was in the
Heathkit SB-10 I used to own but I don't remember it being sealed at all.
I believe it was just crimped in the same 4 places around the bakelite base
as was done with metal tubes.  Though they may have
used different manufacturing methods over the years of production.  I
remember I put a 1kHz signal into the unit and connected the 2 outputs into
the X and Y channels of a scope to see how close it was to producing a 90
degree phase shift.  The display was slightly elliptical but didn't seem
enough so to cause problems.  I also built a replica unit with precision
resistors and silver mica capacitors that gave what appeared to be a
perfect circle on the scope.

I do currently own a NOS Millen 75012 phase-shift unit that uses the same
values of resistors and capacitors as the network in the GE article.  I
opened it up to check the resistors.  All of the resistors are maroon Mepco
1% units of 100k and 133.3k value.  These all measured just within
tolerance (one was 0.9% above nominal).  All of the components are mounted
on a phenolic sheet with 4 compression trimmer capacitors paralleled with
fixed capacitors.  I'll try to find some time to hook this unit up to a
generator and scope like I did with the B&W unit to check its performance.

Sean W0KPX

On Tue, Jul 29, 2025 at 11:04 AM Jim Whartenby via Milsurplus <
milsurplus at mailman.qth.net> wrote:

> If you take a look at the 1961 GE SSB Handbook, PDF page 19, the SSB jr,
> uses a phase shift network.  See:
>
> https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/GE-Books/General-Electric-Sideband-Handbook-1961-Adobe.pdf
> The given resistor tolerances are 1%, the capacitors are paralleled with
> trimmers so a guess is that the capacitors need a similar tight tolerance.
> How these resistor values have held up over 60 years plus is anyone's guess
> but they are certainly not carbon composition resistors.  The act of
> soldering a CC resistor will certainly change it's value making it
> unsuitable for use in the phase shift network.
>
> Jim
>
>
> Logic: Method used to arrive at the wrong conclusion, with confidence.
> Murphy
>
>
> On Tuesday, July 29, 2025 at 10:23:20 AM CDT, kgordon2006 at frontier.com <
> kgordon2006 at frontier.com> wrote:
>
>
> On 29 Jul 2025 at 9:31, Mark K3MSB wrote:
>
> >
> > Hi Hue
> >
> > Were those octal phase shift networks hermetically sealed or in a vacuum?
> >
> > If either, then the resistors may be fine as they are not exposed to
> moisture.
> >
> > 73 Mark K3MSB
>
> They are hermetically sealsd, but not in a vacuumn. As I remember it, the
> resistor values are
> NOT the common ones.
>
> Ken W7EKB
>
>
> >
> >
> >
> > On Tue, Jul 29, 2025 at 4:38AM Hubert Miller <kargo_cult at msn.com> wrote:
> >
> > I have an unused B&W octal base, audio  phase shift thing like in this
> xmtr. Knowing now about
> > how miserably the old carbon resistors like to drift from nominal
> values, i do wonder how far off
> > usable those phasing networks are now.
> > -Hue Miller
> >
> >
> > Sent from my Galaxy
> >
> >
> > ______________________________________________________________
> > 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
> >
>
>
> ______________________________________________________________
> 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
> ______________________________________________________________
> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20250731/742bc7c5/attachment-0001.html>