[Hallicrafters] Piesoelectric effect case in point.

[rbethman]

Pete,

I see loads of disk ceramic or mice used throughout the Halli SX-101 
series, and the SX-111.

They ALL have sub-minis.  Replacing these with OTHER disk caps NOT rated 
for 100MHz is a non-issue!

It isn't rocket science!

NONE of these is dealing with VHF converters.

I also doubt that this was a "significant" issue with the "Twoer" or 
"Sixer", or even the 6N2 equipment.

If it was, then pray tell HOW did this equipment operate so well for so 
long?

Bob - N0DGN

On 1/2/2011 12:32 PM, Peter Bertini wrote:
>
> 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 
> <mailto: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 <mailto:cateswa at msn.com>>
>     > To: "hallicrafters"<hallicrafters at mailman.qth.net
>     <mailto: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.
>