[Heathkit] Calibrating VF-1?
Randy Perkins
w5kcm at sbcglobal.net
Sat Aug 16 23:08:21 EDT 2008
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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