[Hallicrafters] Piesoelectric effect case in point.

[Carl]

Hallicrafters, National and Collins all moved from paper or mylar to disc 
ofetn in a later run of the same product.

The HRO-60 and SP-600 is an excellent point. Both models with factory 
installed ceramic discs are well documented to have better sensitivity at 
10M and 6M than any other type of cap.

The only place National used mylar (in 1960's runs) was where suitable high 
value and high voltage discs were not available such a .05 @ 500V and up. I 
dare anyone to tell me the PP 6V6 audio suffered.

Im going back outside to work on antennas but more will follow after the sun 
goes down.

Carl
KM1H



----- Original Message ----- 
From: "Peter Bertini" <radioconnection at gmail.com>
To: "rbethman" <rbethman at comcast.net>
Cc: "hallicrafters" <hallicrafters at mailman.qth.net>; "Carl" 
<km1h at jeremy.mv.com>; "Walt Cates" <cateswa at msn.com>
Sent: Sunday, January 02, 2011 1:16 PM
Subject: Re: [Hallicrafters] Piesoelectric effect case in point.


> 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.
>>>
>>
>>
>