Topband: Submerging variable caps in oil as substituteforvacuumvariables

[Hardy Landskov]

FYI All,
The HP4815A Vector Impedance Meter submersed the main tuning capacitor in an 
oil bath of some kind to get the capacitance up. Apparently dissipation 
factor was not of concern when the unit was designed. If there are any 
retired HP folks out there they may be able to identify what they used. I 
have read some years ago that hydraulic jack oil was very close.
I need to open mine up and replace one of the capacitors because the 
oscillator will not start on the higher frequency ranges. I am gun shy at 
this point until I know exactly what I am dealing with.
73 Hardy N7RT


----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: "Bill Wichers" <billw at waveform.net>
Cc: <n4zr at contesting.com>; <topband at contesting.com>; "HAROLD SMITH JR" 
<w0rihps at sbcglobal.net>; "Shoppa, Tim" <tshoppa at wmata.com>
Sent: Sunday, February 02, 2014 6:16 AM
Subject: Re: Topband: Submerging variable caps in oil as 
substituteforvacuumvariables


> The major issue with dielectrics is dissipation factor at 2 MHz, which 
> affects losses and Q. Dissipation factor is not published all the time. I 
> can't find dissipation factor for mineral oil.
>
>
>
> ----- Original Message ----- 
> From: "Bill Wichers" <billw at waveform.net>
> To: "Tom W8JI" <w8ji at w8ji.com>
> Cc: "HAROLD SMITH JR" <w0rihps at sbcglobal.net>; "Shoppa, Tim" 
> <tshoppa at wmata.com>; <n4zr at contesting.com>; <topband at contesting.com>
> Sent: Saturday, February 01, 2014 4:05 PM
> Subject: Re: Topband: Submerging variable caps in oil as 
> substituteforvacuum variables
>
>
> I was reading this thread and all the concerns about oil in the capacitor. 
> Has anyone ever thought about trying SF6 as a dielectric? It's commonly 
> used in high voltage (hundreds of kilovolts) switchgear by utilities.
>
> Just a thought, more curiosity than anything else.
>
> -Bill
>
> Sent from my iPhon
>
> On Jan 30, 2014, at 5:32 AM, "Tom W8JI" <w8ji at w8ji.com> wrote:
>
>> Still I am intrigued by the thought of a remote tuning capacitor via 
>> hydraulic tubing :-). The capacitor plates could be as simple as two 
>> concentric cylinder conductors with appropriate spacers. I betcha crud 
>> collecting on the top of the oil would set voltage limit.>>>
>>
>> I would be as concerned, or more concerned, with the dissipation factor 
>> of the oil at short wave frequencies.
>>
>> The thing that worries me is I cannot recall every seeing a single good 
>> high-Q oil-dielectric capacitor above power line and audio frequencies. 
>> As a matter of fact, many years ago I tried to use a surplus 20-40kV oil 
>> capacitor from Fair Radio as a plate blocking capacitor, and it 
>> overheated so badly it exploded.
>>
>> I looked for HF data on mineral oil as a dielectric and couldn't find 
>> anything. That would be my main concern. I guess I could stick mineral 
>> oil between the plates of a capacitor and see what happens to Q.
>>
>>
>> _________________
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>
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