[Hallicrafters] Piesoelectric effect case in point.

[Peter Bertini]

Hello Bob and the group...

It flies because tube boat achor gear was made for frequencies above 54MHz.
Hallicrafters made tube transverters for 144MHz. It might be fun to take a
Twoer and replace the series resonant ceramic bypasses with mylars and see
if it still works.

The problem is tubes have gain well above the operating frequencies covered
by the equipment. My comments were directed to taming VHF and UHF parasitic
problems that can occur in RF and IF stages if the bypassing is
inadequate.    You'll see many radios using low value spoiler resistors on
grid and plate leads to address that issue, or a few hundred ohm value
resistor on the screen, long with good bypassing practices to control
unwanted parasitics. This may be a non issue with 6SK7s, but for many of the
more popular 7 pin minatures bypassing can be quite critical.

Pete
On Sun, Jan 2, 2011 at 11:58 AM, rbethman <rbethman at comcast.net> wrote:

> This whole thread just doesn't fly for the Hallicrafters, Boatanchors,
> Heathkits, Nationals and the like.
>
> The entirety of the "Kemet" document referenced, has to do with
> MICROWAVE applications!
>
> READ the tables.  Do you find ANYTHING below 100 MHz?
>
> So how would "our" bypassing and blocking in equipment apply since at
> the highest, we only get to 54MHz?
>
> Walt - you've got apples and oranges.
>
> Bob - N0DGN
>
> On 1/2/2011 11:10 AM, Carl wrote:
> > Walt, That is a bit of a stretch to attempt to prove a point you only
> tried
> > to make yesterday.
> >
> > I would suspect that putting that cap on a TC-6A or other high end cap
> > tester at rated voltage you will discover the actual reason for the
> failure.
> > My bet would be on a internal fracture which are far from an unknown
> failure
> > mode.
> >
> > Nobody is questioning the piezo effect in ceramic caps, it is how and
> when
> > they manifest themselves that is surrounded by hype that ripples down and
> > starts a great panic among the unwashed hordes.
> >
> > If you really want to do a service then take that radio, hook it to a
> scope
> > and HP Distortion Analyzer and run tests with various construction new
> > production capacitors. Run it at audio levels that are within the range
> of
> > the radio.
> >
> > Carl
> > KM1H
> >
> >
> >
> >
> > ----- Original Message -----
> > From: "Walt Cates"<cateswa at msn.com>
> > To: "hallicrafters"<hallicrafters at mailman.qth.net>
> > Sent: Saturday, January 01, 2011 10:09 PM
> > Subject: [Hallicrafters] Piesoelectric effect case in point.
> >
> >
> >> As luck would have it, today I have a SR-150 in the lab that suffers
> from
> >> "microphonics". It was easy enough to localize the area by lightly
> tapping
> >> the chassis with a plastic tuning wand. I turned the rig over and
> started
> >> tapping components. Sure enough it was C64 a .01uf ceramic disk. This
> >> capacitor couples the audio output from the product detector to the
> first
> >> audio amp. When replaced with a modern poly cap the microphonic
> condition
> >> was eliminated.
> >>
> >> What I have noted over the years is that ceramic disk capacitors used as
> >> coupling capacitors seem to be more vulnerable to this condition. This
> is,
> >> as the Kemet report states because of the high difference of potential
> >> across the dielectric and termination into a high impedance. In this
> case
> >> with the SR-150 one side is 250v the other side is zero volts. However
> the
> >> low side sees a relatively high impedance of 500k. When there is receive
> >> signal present with a strong audio the pieso effect ( that is its
> >> susceptibility to vibration ) is dampened. When you remove the signal
> and
> >> there is no audio present the pieso effect into the high Z of the AF
> GAIN
> >> pot (500k) supports the effect and the microphonics gets much more
> >> pronounced.
> >>
> >> Best Regards, Walt Cates, WD0GOF,
> >> http://www.myhamshack.com/WD0GOF/<http://www.myhamshack.com/WD0GOF/>
> >>
> >> I pity the self made man, he is definitely working at a disadvantage. I
> >> cherish the help from God, family and mentors.
> >> ______________________________________________________________
> >> Hallicrafters mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/hallicrafters
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:Hallicrafters at mailman.qth.net
> >>
> >> List Administrator: Duane Fischer, W8DBF
> >> ** For Assistance: dfischer at usol.com **
> >>
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> > ______________________________________________________________
> > Hallicrafters mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/hallicrafters
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Hallicrafters at mailman.qth.net
> >
> > List Administrator: Duane Fischer, W8DBF
> > ** For Assistance: dfischer at usol.com **
> >
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
>
> --
> +------------------------------------------------------------------+
> |               AM Amateur Radio Operator    NØDGN                 |
> +------------------------------------------------------------------+
> |               http://home.comcast.net/~rbethman/                 |
> +------------------------------------------------------------------+
> | Bob Bethman                \\\|///     " The absence of a danger |
> |                           \\ ~ ~ //      signal does *NOT* mean  |
> | rbethman at comcast.net      (/ @ @ /)      that everything is OK " |
> +----------------------o00o---°(_)°---o00o-------------------------+
>
> ______________________________________________________________
> Hallicrafters mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hallicrafters
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Hallicrafters at mailman.qth.net
>
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>