[Hallicrafters] Piesoelectric effect case in point.

[Peter Bertini]

On Sun, Jan 2, 2011 at 12:49 PM, rbethman <rbethman at comcast.net> wrote:

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

*Absolutely correct. And you will find them working well in tons of
commercial two-way gear, consumer products,  and other ham equipment as
well.*

>
> They ALL have sub-minis.  Replacing these with OTHER disk caps NOT rated
> for 100MHz is a non-issue!
>
> I* agree completely. I'd replace a disk cap with another disk cap.   I
wouldn't replace a mylar coupling cap with a disk ceramic in a high end
piece of audio gear because of the harmonic distortion issues. For
communications grade audio it is probably a non issue. Ceramic caps are
ideal for low impedance bypassing requirements.  *

It isn't rocket science!

 I also doubt that this was a "significant" issue with the "Twoer" or
"Sixer", or even the 6N2 equipment.
*It would be an issue if someone replaced the ceramic disks with mylars and
expected it to still work. My comments were concerned about the first post
in this thread, which I interpreted to read as saying that mylars or ODs are
better than ceramics.  *
If it was, then pray tell HOW did this equipment operate so well for so
long?

*Because the engineers used ceramic disks for two reasons: low cost and
effectiness for the applications at hand.*
**
*I think there was some misunderstanding of what I was saying due to the
medium at hand :) We seem to be on the same page.*

Pete



> 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> 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.
>>
>
>