[Test-Equipment] Millen GDO question

Mon Aug 1 00:52:27 EDT 2011

thnx

-----Original Message-----
From: test-equipment-bounces at mailman.qth.net
[mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Carl
Sent: Sunday, July 31, 2011 6:34 PM
To: Discussion of Electronic Test Equipment
Subject: Re: [Test-Equipment] Millen GDO question

Mouser catalog


----- Original Message ----- 
From: "Randy D. Hunt" <randy_hunt960 at yahoo.com>
To: "'Discussion of Electronic Test Equipment'" 
<test-equipment at mailman.qth.net>
Sent: Sunday, July 31, 2011 9:15 PM
Subject: Re: [Test-Equipment] Millen GDO question


> That's good to know as I was not aware that they went up that high.  Do 
> you
> have any links to sources?
>
> Randy, KI6WAS
>
> -----Original Message-----
> From: test-equipment-bounces at mailman.qth.net
> [mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Carl
> Sent: Sunday, July 31, 2011 4:17 PM
> To: Discussion of Electronic Test Equipment
> Subject: Re: [Test-Equipment] Millen GDO question
>
> Thats ancient history. They now have HV film resistors the size of a 1W
> carbon good for 5KV and others much higher. They are not that expensive
> either, I use them in ham amps as the string to the voltmeter.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- 
> From: "Randy D. Hunt" <randy_hunt960 at yahoo.com>
> To: "'Discussion of Electronic Test Equipment'"
> <test-equipment at mailman.qth.net>
> Sent: Sunday, July 31, 2011 6:45 PM
> Subject: Re: [Test-Equipment] Millen GDO question
>
>
>> Carbon Comps have another advantage - higher voltage rating.  That's why
>> you
>> find them in voltage divider strings in things like "scopes". . .
>>
>>
>> Randy
>> -----Original Message-----
>> From: test-equipment-bounces at mailman.qth.net
>> [mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Fuqua, Bill 
>> L
>> Sent: Sunday, July 31, 2011 12:01 PM
>> To: Richard Knoppow; Discussion of Electronic Test Equipment; Mike Manes
>> Subject: Re: [Test-Equipment] Millen GDO question
>>
>> Not that this has much to do with this issue but some components values
>> change over 50 or more years.
>>
>> From: test-equipment-bounces at mailman.qth.net
>> [test-equipment-bounces at mailman.qth.net] On Behalf Of Richard Knoppow
>> [1oldlens1 at ix.netcom.com]
>> Sent: Sunday, July 31, 2011 10:38 AM
>> To: Mike Manes; Discussion of Electronic Test Equipment
>> Subject: Re: [Test-Equipment] Millen GDO question
>>
>> Carbon composition resistors are very bad. In our stock room we had some
>> carbon comp resistors that
>> were not only out of tolerance but were up to the next 10% value and they
>> were only 10 years old!
>> The upper values were the worst. The 1 Meg and above were way off and had
>> increased in value 50% or more
>> in some cases. Under use they can change value even more.
>>  Much of the stuff made in WWII or soon after may have resistors may be
>> way
>> off value.
>> I wonder if some of the resistors that were treated or coated retained
>> their
>> value better than the non-coated ones.
>> It seems to me that the oil component of the carbon comp dries up, you 
>> can
>> see if apply several time its rated
>> power. It will sweat or bubble oil onto the surface. And after the test
>> its
>> value will be somewhat greater.
>> We replace all our carbon comp resistors with carbon films. The carbon
>> comps
>> had several advantages but
>> we just could not let them die while sitting in the stock room. Now they
>> are
>> very hard to get.
>> The carbon film resistors can burn out without any outward sign of damage
>> and if the epoxy coating is damaged
>> they can easily short out.
>>   We got some Tektronix 2200 series scopes that started having focus
>> problems not long after receiving them
>> Discovered a long voltage divider string on the HV supply had carbon comp
>> resistors.  They possibly used them
>> because they could be put next to the circuit board without worry of
>> arcing.
>> But, they increased in value and
>> the scopes failed. We replaced them with carbon film resistors and placed
>> them about a 1/4 inch above the PCB.
>> Since these were in instructional labs we could not wait forTektronix to
>> repair them under warranty.
>>
>> 73
>> Bill wa4lav
>>
>>
>> ----- Original Message -----
>> From: "Mike Manes" <mrmanes at gmail.com>
>> To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; "Discussion
>> of Electronic Test Equipment"
>> <test-equipment at mailman.qth.net>
>> Sent: Saturday, July 30, 2011 8:37 PM
>> Subject: Re: [Test-Equipment] Millen GDO question
>>
>>
>>> Hi Richard,
>>>
>>> That's pretty characteristic of every GDO I've used,
>>> including the
>>> Millen, a Knightkit and a really nice piece of homebrew
>>> work. I
>>> think it has to do with the low VHF Q of the air variable
>>> cap that's
>>> necessary to get a decent L/C ratio and tuning range on
>>> the HF
>>> bands.  I've seen GDOs that are specifically designed for
>>> VHF and
>>> UHF, and tho I haven't used one, I'd expect them to
>>> overcome that
>>> problem.
>>>
>>> 73 de Mike W5VSI
>>>
>>   Thanks Mike, that's what I wanted to know. I think mine
>> is working as it should. The low limit of the coil is given
>> as 140mhz. The dial is calibrated down to 125mhz. The grid
>> current shows some indication down to maybe 130mhz. So, it
>> covers the range specified, just not the complete range
>> shown on the dial. The next lowest range goes up high enough
>> to provide some overlap.
>>
>>
>> --
>> Richard Knoppow
>> Los Angeles
>> WB6KBL
>> dickburk at ix.netcom.com
>>
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