[Heathkit] Calibrating VF-1?
Bob Macklin
macklinbob at msn.com
Sat Aug 16 23:21:56 EDT 2008
That's great!
Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "Randy Perkins" <w5kcm at sbcglobal.net>
To: "Bob Macklin" <macklinbob at msn.com>
Cc: <w5rkl at yahoo.com>; "Kevin Ward" <n2ie at arrl.net>;
<heathkit at mailman.qth.net>
Sent: Saturday, August 16, 2008 8:08 PM
Subject: Re: [Heathkit] Calibrating VF-1?
> Hello Bob, and others,
>
> It looks like I found the problem with the VF-1. Both of the trimmer
> capacitors used to align the frequency are bad. I worked on the VF-1
> today and had the same result as before. I was unable to get the
> frequency down low enough. I tried soldering a 35 pf across the 160
> meter trimmer capacitor and the frequency dropped down to about 1630
> Khz. I tried the same thing on 40 meters and had similar results. I
> replaced both trimmers with the ones in my "parts vf-1". Now I am able
> to adjust the frequency easily well below the bands even with the coil
> cores backed way out. After changing the trimmer caps out the VF-1
> aligned properly and the calibration is correct through out the range.
> So far it is still working well.
> Thank you for the help in getting this going. Now I am another step in
> getting everything going all at once.
> 73, Randy, W5KCM
>
> Bob Macklin wrote:
> > On the low position the VFO will make it's output from 1750 to 2000. You
> > should be able to measure this with your counter.
> >
> > The coil should allow you to tune through 1750. In fact you have to be
able
> > to tune through 1750.
> >
> > The low position uses a 47pf and 10pf in parallel. The first thing it to
be
> > sure the solder connections and the grounding of the solder lug are
good.
> >
> > DM-15 capacitors are "Dipped Mica" capacitors. They are the most common
form
> > of mica capacitors available today other than surface mount types Here
is
> > the Mouser page for these items:
> > http://www.mouser.com/catalog/635/829.pdf
> >
> > I would suggest replacing the 10f and 47pf capacitors with a 62pf dipped
> > mica to test the tuning range. If the oscillator still cannot be
calibrated
> > the problem is either with the coil or the main tuning cap.
> >
> > You might consider replacing the main tuning capacitor (35pf) with a
33pf or
> > 36pf dipped mica for testing. If you do this and the oscillator will
still
> > not tune to 1750 then the problem has to be the coil.
> >
> > Bob Macklin
> > K5MYJ
> > Seattle, Wa,
> > "Real Radios Glow in the Dark"
> >
> > ----- Original Message -----
> > From: "Randy Perkins" <w5kcm at sbcglobal.net>
> > To: "Bob Macklin" <macklinbob at msn.com>
> > Cc: <w5rkl at yahoo.com>; "Kevin Ward" <n2ie at arrl.net>;
> > <heathkit at mailman.qth.net>
> > Sent: Tuesday, August 12, 2008 11:18 AM
> > Subject: Re: [Heathkit] Calibrating VF-1?
> >
> >
> >> Hi Bob,
> >>
> >> Thanks for the frequency info. I believe that will help.
> >>
> >> The only thing I have that will measure capacitance is my Fluke 79 DVM.
> >> I do not believe that it will measure small value capacitors. I do have
> >> a pretty good assortment of the small brown silver mica caps that I
> >> could use for testing. I looked at my "parts vf-1" and one of these
> >> fixed caps has been removed. I am not familiar with the "DM-15" type of
> >> capacitor.
> >>
> >> I will have to check that where the core is going into the coil. It
> >> seems that with the core fully inside the coil, I can still see the
back
> >> of the core. It is about a 1/4" inside the ceramic form. It doesn't
seem
> >> to travel very far inside. I don't recall seeing the frequency output
> >> hit a low point and then start increasing as the core is turned farther
> >> into the coil. It does act like it needs more inductance. It doesn't
> >> seem like the core is making it to the center of the coil. I will check
> >> for this again.
> >>
> >> I had been trying several methods to measure the frequency. First I
> >> started with my Kenwood R-1000 receiver and this worked well, just not
> >> very accurate. Then I measured the output frequency of the AT-1
> >> transmitter with the frequency counter (Fluke 1912A). This seems to
work
> >> well. I did try measuring the output direct from the VFO with the
> >> frequency counter with mixed results.
> >> What about feeding the VFO output direct into a 50 ohm load then
connect
> >> the frequency counter across this load? With the info you gave me
above,
> >> I will only need to use the AT-1 for power. This way I can eliminate
the
> >> AT-1 possibly causing some of the issues.
> >>
> >> Randy
> >>
> >> Bob Macklin wrote:
> >>> For the low position (160/80/40) the oscillator tunes 1750 to 2000.
> >>>
> >>> For the middle position (40/20/15/10) the oscillator tune 7000 to
7425.
> >>>
> >>> In both positions there are 2 fixed capacitors. I suspect these have
> >>> different temp coefficients for temperate compensation. One of these
> > being
> >>> bad may be limiting the low range. They could be replaced by DM-15
type
> >>> capacitors for testing.
> >>>
> >>> Do you have a way to measure the value of small capacitors?
> >>>
> >>> The coil should not be all the way in. Also the maximum inductance is
> > when
> >>> the iron core is centered in the coil. It should go through maximum
> >>> inductance when being adjusted. While adjusting it should reach the
> > lowest
> >>> frequency then start increasing in frequency again.
> >>>
> >>> How are you measuring the frequency?
> >>>
> >>> Bob Macklin
> >>> K5MYJ
> >>> Seattle, Wa,
> >>> "Real Radios Glow in the Dark"
> >>>
> >>>
> >>> ----- Original Message -----
> >>> From: "Randy Perkins" <w5kcm at sbcglobal.net>
> >>> To: "Bob Macklin" <macklinbob at msn.com>
> >>> Cc: <w5rkl at yahoo.com>; "Kevin Ward" <n2ie at arrl.net>;
> >>> <heathkit at mailman.qth.net>
> >>> Sent: Monday, August 11, 2008 5:54 PM
> >>> Subject: Re: [Heathkit] Calibrating VF-1?
> >>>
> >>>
> >>>> Hi Bob,
> >>>>
> >>>> The closest I can get the calibration at 3500 is 3550. That is with
the
> >>>> 160 meter coil core adjusted all the way inside the coil (min screw
> >>>> exposed). This seems to be related to where the output coil is
> > adjusted.
> >>>> I followed the instructions in the manual and adjusted the dial to
the
> >>>> mark | just left of the 7000 with the capacitor fully meshed with the
> >>>> larger stator section. The trimmer capacitor has a very small effect
on
> >>>> the frequency. Possibly this may be a clue. Possibly one of the 10 or
> > 47
> >>>> pf fixed caps may be bad? I will have to disassemble the sub-chassis
to
> >>>> get to these.
> >>>> Do you know the exact fundamental frequencies that I should see at
the
> >>>> output of the VFO on each band at the end of each dial range?
> >>>>
> >>>> Thanks, Randy
> >>>>
> >>>> Bob Macklin wrote:
> >>>>> The way I adjust these units is to use the inductor to adjust the
low
> >>> end
> >>>>> (ie. 3500) and the trimmer to adjust the high end (ie. 4000).
> >>>>>
> >>>>> With the main tuning capacitor fully meshed (dial on the 3500
> > position)
> >>> can
> >>>>> you adjust the inductor to 3500 in the 80M position?
> >>>>>
> >>>>> Bob Macklin
> >>>>> K5MYJ
> >>>>> Seattle, Wa,
> >>>>> "Real Radios Glow in the Dark"
> >>>>> ----- Original Message -----
> >>>>> From: "Randy Perkins" <w5kcm at sbcglobal.net>
> >>>>> To: <w5rkl at yahoo.com>
> >>>>> Cc: "Kevin Ward" <n2ie at arrl.net>; "Bob Macklin"
<macklinbob at msn.com>;
> >>>>> <heathkit at mailman.qth.net>
> >>>>> Sent: Monday, August 11, 2008 5:22 PM
> >>>>> Subject: Re: [Heathkit] Calibrating VF-1?
> >>>>>
> >>>>>
> >>>>>> Hi Mike,
> >>>>>>
> >>>>>> I have been told by some others that the 160 meter coil normally
has
> >>>>>> that gap near the end. It measures about 6.5 Ohms DC resistance. It
> > is
> >>>>>> difficult to count the turns due to the wire is extremely small
(AWG
> > #
> >>>>>> 30+). After closer inspection, I doubt that the coil has been
> > modified,
> >>>>>> it has several coats of varnish.
> >>>>>> I did check the 2.2 K and 22 K ohm resistors and they check pretty
> >>>>>> close. I have gotten quite a few suggestions of things to check so
I
> >>>>>> have my work cut out for me.
> >>>>>> Thanks, Randy, W5KCM
> >>>>>>
> >>>>>> Michael Waldrop wrote:
> >>>>>>> Hi Randy,
> >>>>>>>
> >>>>>>> Missing turns on the 160 meter coil will definitely creates an
> >>> alignment
> >>>>>>> issue, at least on
> >>>>>>> the low bands.
> >>>>>>>
> >>>>>>> I doubt the coil's wire gauge is heavy. Maybe someone has an
> > original
> >>>>>>> unmodified VF-1
> >>>>>>> that can determine the wire size and turns. If you rewound the
coil
> >>> you
> >>>>>>> would have to
> >>>>>>> ensure the coil is stable and does not move around or is lose on
the
> >>>>>>> form. A couple coats
> >>>>>>> of varnish could do this. The wire sould be solid enamel wire
which
> >>> can
> >>>>>>> be obtained at
> >>>>>>> various parts outlets on the Internet.
> >>>>>>>
> >>>>>>> 73
> >>>>>>> Mike
> >>>>>>> W5RKL
> >>>>>>>
> >>>>>>>
> >>>>>>> 73
> >>>>>>> Mike
> >>>>>>> W5RKL
> >>>>>>>
> >>>>>>> --- On *Mon, 8/11/08, Randy Perkins /<w5kcm at sbcglobal.net>/*
wrote:
> >>>>>>>
> >>>>>>> From: Randy Perkins <w5kcm at sbcglobal.net>
> >>>>>>> Subject: Re: [Heathkit] Calibrating VF-1?
> >>>>>>> To: w5rkl at yahoo.com
> >>>>>>> Cc: "Kevin Ward" <n2ie at arrl.net>, "Bob Macklin"
> >>>>>>> <macklinbob at msn.com>, heathkit at mailman.qth.net
> >>>>>>> Date: Monday, August 11, 2008, 1:04 PM
> >>>>>>>
> >>>>>>> Thanks Mike. I will check the two resistors. I picked up this
> > VF-1
> >>> a
> >>>>>>> while back at a hamfest and it is very clean and looks to be
put
> >>>>>>> together very well. Possibly it has not been used in many
years.
> >>> One
> >>>>>>> thing I noticed is that the 160 meter coil looks to have some
> >>> turns
> >>>>>>> removed near the end of the coil. Possibly someone knows
exactly
> >>> how
> >>>>>>> many turns and what size if wire should be on this coil.
> >>>>>>>
> >>>>>>> Thanks, Randy, W5KCM
> >>>>>>>
> >>>>>>> Michael Waldrop wrote:
> >>>>>>> > You might want to perform the voltage checks on page 18 of
the
> >>>>> manual. I
> >>>>>>> also
> >>>>>>> > recommend checking the two grid leak resistors, 2.2K and
22K.
> >>> The
> >>>>> VF-1 is
> >>>>>>> quite
> >>>>>>> > old and with age resistors can and will change values which
> > will
> >>>>> affect
> >>>>>>> the oscillator.
> >>>>>>> >
> >>>>>>>
> >>>>>>> > 73
> >>>>>>> > Mike
> >>>>>>> > W5RKL
> >>>>>>> >
> >>>>>>> >
> >>>>>>> > --- On Sun, 8/10/08, Bob Macklin <macklinbob at msn.com> wrote:
> >>>>>>> > From: Bob Macklin <macklinbob at msn.com>
> >>>>>>> > Subject: Re: [Heathkit] Calibrating VF-1?
> >>>>>>> > To: "Kevin Ward" <n2ie at arrl.net>
> >>>>>>> > Cc: heathkit at mailman.qth.net
> >>>>>>> > Date: Sunday, August 10, 2008, 9:50 PM
> >>>>>>> >
> >>>>>>> > Does it jump as you are changing the position of the main
> > tuning
> >>>>> capacitor
> >>>>>>> > or as you are adjusting the coil?
> >>>>>>> >
> >>>>>>> > If the coil is all the way to the max inductance you may
have
> > an
> >>>>> bad or
> >>>>>>> > unsoldered capacitor.
> >>>>>>> >
> >>>>>>> > One thing to do is unscrew any solder lugs associated with
the
> >>>>> tuning
> >>>>>>> > elements and retighten them.
> >>>>>>> >
> >>>>>>> > Bob Macklin
> >>>>>>> > K5MYJ
> >>>>>>> > Seattle, Wa,
> >>>>>>> > "Real Radios Glow in the Dark"
> >>>>>>> > ----- Original Message -----
> >>>>>>> > From: "Kevin Ward" <n2ie at arrl.net>
> >>>>>>> > To: "Bob Macklin"
> >>>>>>> <macklinbob at msn.com>
> >>>>>>> > Cc: "Randy Perkins" <w5kcm at sbcglobal.net>;
> >>>>>>> > <heathkit at mailman.qth.net>
> >>>>>>> > Sent: Sunday, August 10, 2008 7:21 PM
> >>>>>>> > Subject: Re: [Heathkit] Calibrating VF-1?
> >>>>>>> >
> >>>>>>> >
> >>>>>>> >> Randy -
> >>>>>>> >>
> >>>>>>> >> I agree with Bob - look closely at the main tuning
capacitor,
> >>>>>>> >> particularly the rotor wipers. As to the drive issue; look
> > in
> >>>>> the
> >>>>>>> AT-1
> >>>>>>> >> manual. IIRC, there is a circuit change for the crystal
> >>>>> oscillator to
> >>>>>>> >> kill the feedback and make it behave as a buffer.
> >>>>>>> >>
> >>>>>>> >> Kevin N2IE
> >>>>>>> >>
> >>>>>>> >>
> >>>>>>> >
> >>>>>>> >
> >>>>>>> >
> >>>>>>> >
> >>>>>>> >
> >>>>>>> >
> >>>>>>>
> >>>>>>>
> >>>
> >
> >
>
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