I contacted George A. Sanford about the oil used in the variable cap in the
HP4815a and he replied that the oil was used for a shock absorber effect for
frequency stability in the instrument and not for any other reason. I had a
need for a vac variable and have a large air variable that I had planed to
submerge in oil, but have not yet found a suitable oil.
73 es DX Pat H. Armstrong KF5YZ
---- Carl <km1h@jeremy.mv.com> wrote:
> There are several on the HP forum that are famililar with that product
> Hardy.
> I also have one but claim no expertise since it still works well.
> hp_agilent_equipment@yahoogroups.com
>
> Carl
> KM1H
>
> ----- Original Message -----
> From: "Hardy Landskov" <n7rt@cox.net>
> To: "Tom W8JI" <w8ji@w8ji.com>; "Bill Wichers" <billw@waveform.net>
> Cc: <n4zr@contesting.com>; <topband@contesting.com>; "HAROLD SMITH JR"
> <w0rihps@sbcglobal.net>; "Shoppa, Tim" <tshoppa@wmata.com>
> Sent: Sunday, February 02, 2014 8:58 AM
> Subject: Re: Topband: Submerging variable caps in oil
> assubstituteforvacuumvariables
>
>
> > 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@w8ji.com>
> > To: "Bill Wichers" <billw@waveform.net>
> > Cc: <n4zr@contesting.com>; <topband@contesting.com>; "HAROLD SMITH JR"
> > <w0rihps@sbcglobal.net>; "Shoppa, Tim" <tshoppa@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@waveform.net>
> >> To: "Tom W8JI" <w8ji@w8ji.com>
> >> Cc: "HAROLD SMITH JR" <w0rihps@sbcglobal.net>; "Shoppa, Tim"
> >> <tshoppa@wmata.com>; <n4zr@contesting.com>; <topband@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@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.
> >>>
> >>>
> >>> _________________
> >>> Topband Reflector Archives - http://www.contesting.com/_topband
> >>
> >>
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> >> Checked by AVG - www.avg.com
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> >>
> >>
> >> _________________
> >> Topband Reflector Archives - http://www.contesting.com/_topband
> >>
> >
> >
> > _________________
> > Topband Reflector Archives - http://www.contesting.com/_topband
> >
> >
> > -----
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>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
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