[Heathkit] Calibrating VF-1?
Randy Perkins
w5kcm at sbcglobal.net
Tue Aug 12 14:18:56 EDT 2008
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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