The video is the description in its entirety .
Virtually all vintage ham equipment posted on E-Bay is untested. The biggest reason is it is an estate seller who has no idea what it is, much less test it.
The second reason you see, "untested", is probably it was tested and it doesn't work.
Due to the increasing number of "not as described" scammer cases, I am forced to offer all of the electronic items *as is* without any refunds or returns - All sales final.
The reason I do a video is for you to see a sample of it working, I want you to buy with confidence and frankly I also wanted to be protected against frivolous complaints.
Track your purchase so you will be home at delivery, not responsible for theft.
What EBay comments really mean:
"I don't know if it works" = It does not work.
"I am unable to test the item." = It does not work.
"I don't know anything about ham gear." = It does not work.
"Powers on." = It does not work.
"Lights up." = It does not work.
"I am afraid to plug it in." = It does not work.
"It made sounds." = It does not work.
"I do not have an antenna to test it." = It does not work.
Heathkit Model VF-1
VFO
Design Commentary
Everything You Wanted
To Know About The VF-1 But Were Afraid To Ask
David W. Ishmael - WA6VVL
Just
a few design notes in no order of importance:
- The Heathkit Model VF-1 VFO, announced
in the Summer of 1954, covers 7 bands, 160M - 11M, in 3 switch positions
(160/80/40, 40/20/15/10, and 11).
Measuring 7”H x 6-1/2”W x 7”D, it weighs 4 lbs. Its tube compliment is a single 6AU6,
used as a Clapp oscillator, and a 0A2, 150V voltage regulator. It sold for $19.50.
- Mechanically, and
electrically, the VF-1 is relatively simple. A separate LC network is used for 160M
and another is used for 40M. For
11M, a variable trim capacitor is added to the 40M LC network. Assembly and wiring is very
straight-forward, and can easily be accomplished in two evenings work.
- When announced in the
Summer of 1954, the VF-1 had a copper-plated chassis. Sometime around mid-1958, Heathkit changed the VF-1 chassis
to non-copper-plated until it was discontinued in 1961, replaced by the
HG-10.
- The VF-1’s dial is
very easy to read and has a green glow due to the green filter behind the
dial, illuminated by a #47 bulb.
The green filter is split in the middle creating a narrow, white,
fiducial for setting the desired output frequency. Installing a 10 ohm 1/2W resistor is
series with the #47 bulb will lengthen its life and reduce the dial
illumination a bit.
- The main tuning
capacitor is an E.F. Johnson P/N
169-36. It is a special build for
the VF-1. It is a dual-variable
with a specified maximum capacity of 35uufd (160M) and 11uufd (40M),
comprised of 5 and 2 stator plates respectively. It is NOT an off-the-shelf “catalog P/N”.
- The Summer of 1954
flyer announcing the VF-1 has a close-up photo of the main tuning
capacitor. It is NOT the same one used in later
production VF-1s. The one in the
photos is bolted together and the production version is soldered. It’s also clear from the schematic that
accompanies the flyer that the
temperature compensating capacitors and their value had been determined
with the bolted version. The
temperature coefficient of that variable depends on the linear temperature
coefficient of the expansion of the metal used - brass being the most
common. However, the capacitor’s
structural rigidity is also
important, and in this regard, there are clear differences between the two
variables.
- The VF-1’s friction
dial-drive is a bit clever. The
front panel is slotted for the installation of the ¼” drive-bushing and
friction drive shaft which engages the circular cutout in the plastic dial
disk. The plastic dial disk is
0.030” thick. Some experimentation
is required to get the engagement “just right”. Too loose and it will slip. Too tight and it’s difficult to
turn. That’s why the hole in the
front panel is slotted. The
procedure I’ve used over the years is to press down on the top of the
bushing with a short length of 0.062” PCB material, applying even pressure
while the bushing’s 3/8” nut is tightened using a 3/8” nut-driver. However, here’s the problem with the
VF-1’s dial drive: to cover the entire 160M/80M, it takes less than two
revolutions of the main tuning knob - about 1.8 to be precise. And about 1.3 to cover the 40M
band. There’s just not enough
resolution to precisely set any given frequency. Compare this to the Heathkit HG-10’s relatively complicated 28:1 gear
drive vernier tuning system. Hint: during the rebuild of VF-1 #3, the dial
assembly’s 4-40 hardware was rusted.
I replaced it w/new 4-40 pan-head screws and 4-40 nuts. However, after the final assembly, the
dial wouldn’t turn more than about 90°!!
Turns out that the 0.200” diameter of the new 4-40 screws caused an
interference-fit with the friction drive!!
I kissed each screw with a bench grinder and then positioned each
screw on the dial assembly to avoid the interference-fit. Hint: the easiest way to install the front
panel and the friction drive components is to mount the friction drive and
¼” bushing to the dial assembly at the bottom, engaging the dial, and then
just lay the front panel over the two switches and the bushing..
- The 160M coil is
divided into two sections - 82T and 4T separated by 0.3” on a 0.87
dia. Ceramic coil form. I think the intent of the design is that adjustable
core interacts more with the 4T coil than the larger 82T coil. The
VF-1's schematic says the coil is 114.5 uHy. In the 40M position,
with one end of the 160M coil not connected to anything other than the open
switch contact, the 160M inductor measured 109.6 uHy. The calculated
inductance of the coil, assuming 86T and a coil length of 1.06”, and no
core, is 96.4 uHy. The coil, without its core measures 102.2 uHy. It should be noted that I have several archival
photos that shows one continuous winding of the 160M coil -
no separation - on both copper-plated and non-copper-plated
chassis..
- The 40M coil is also
divided into two sections - 17T and 5T separated by 1/8" on a 0.87
dia. Ceramic coil form. I think the intent of the design is that adjustable
core interacts more with the 5T coil than the larger 17T coil. The
VF-1's schematic says the coil is 9.3uHy. In the 160M position, with
one end of the 40M coil not connected to anything other than the open switch
contact, the 40M inductor measured only 7.6 uHy. The calculated
inductance of the coil, assuming 22T and a coil length of 0.64”, and no
core, is 8.88 uHy. The coil, without its core, measures 7.8 uHy.
- Per Heathkit, the 160M and 40M coils
are wound w/Litz or double cellulose wire coated w/Polystyrene cement and
baked for humidity protection.
- The iron cores are
identical for both coils and measure approximately 0.73”L x 0.42”
Dia. They are mounted on a length
of 6-32 brass stock approximately 1.25”L and slotted at the end for
adjustment. However, the length of
their 6-32 bushings plus their 6-32 “jam-nuts”, limits the maximum
adjustment range to approximately 0.8”.
- The primary frequency
determining components for the 160M band are: the 35uufd variable, a
4.5-25uufd NPO ceramic variable trim capacitor, a 47uufd silver mica
capacitor, and a 10uufd N750 ceramic capacitor.
- The primary frequency
determining components for the 40M band are: the 11uufd variable, a
4.5-25uufd NPO ceramic variable trim capacitor, a 22uufd silver mica
capacitor, and a 4.7uufd N750 ceramic capacitor.
- The 11M band uses an
additional 4.5-25uufd NPO ceramic variable trim capacitor to obtain 6.740
MHz - 6.808 MHz when switched into the 40M LC network.
- There is a
dual-section coil assembly in the plate of the 6AU6. It is comprised of two coils in series.
The top coil is for 160M and is specified at 50-150 uHy. The bottom coil is for 40M and is
specified at 5-15 uHy. The top coil
is shorted out in the 40M and 11M positions. In my rebuilt unit, those coils measured
70.6 uHy (pins 1 and 2) and 5.4 uHy (pins 2 and 3) respectively. Both are slug-tuned and adjustable.
- The bandswitch is
essentially a 3-position 3-pole switch on a single ceramic wafer. Like many Heathkit parts, this is also not an off-the-shelf item,
although a standard 3-pole 3-position ceramic switch could be made to
work. The ceramic wafer is at the
end of 1-3/4” 4-40 spacers, and I have found that there is a certain
degree of flexing as the switch is turned, causing some mis-alignment of
the contacts. When I rebuilt my
VF-1, I shortened these spacers to ½”, and cut down the switch
accordingly.
- The OFF/STANDBY/ON
switch is a 1-pole 3-position progressively shorting phenolic switch.
- The VF-1 manual, P/N
595-91, dated 1954, specifies the power requirements: 6.3 Vac @ 0.45A, and
250-350 Vdc @ 15-20 mA. Experience
has shown that the B+ power requirements can easily exceed 25 mA in
40M. However, the VF-1 was designed
as a companion to the Heathkit Model
AT-1 4-band 25W Amateur CW Transmitter which was announced in the Spring
of 1953. The AT-1’s B+ can easily
exceed 500 Vdc key-up (see below), and, the VF-1’s power cable is
terminated for use with the AT-1.
- Using my rebuilt VF-1
as a “benchmark”, the power supply current at 160M and 40M at a supply
voltage of 300 Vdc is14.83 mA and 21.36 mA respectively. This translates into a power consumption
in the box of 7.3W and 9.2W respectively.
On Sunday 10Feb19 and
Monday 11Feb19, the measured
temperature-rise at 160M and 40M after 60 minutes of operation was 8.3°C
and 10.1°C
respectively.
- At a supply voltage
of 300 Vdc, the 15K 5% 10W dropping resistor for the 150 Vdc 0A2 regulator
tube is only dissipating 1.5W.
However, the VF-1 is designed to be used with the Heathkit AT-1 transmitter. At key-up, the AT-1’s B+ measured 523
Vdc @ 115 Vac line voltage. Under those conditions, that 15K is
now dissipating 9.28W!!! That
resistor, for use with the AT-1, should be at least a 15W-20W wirewound
resistor!!! 9.28W is a recipe for
early failure, especially with the typical construction of a 10W
cement-block resistor!!! Well, the
situation gets much worse. The VF-1
is also widely used with the Heathkit
DX-20 CW Transmitter. At
key-up, the DX-20’s B+ was 599.4 Vdc at 115 Vac line voltage!! Under
those conditions, that 15K is now dissipating 13.46W!!! It should be noted that there is NO accessory socket on the DX-20
for connecting the VF-1, and the DX-20 manual clearly indicates using a
separate power supply for the VF-1.
However…………...
- It should also be
noted that the original P/N 595-91 manual indicates that the series-dropping resistor for the 0A2
is a 15K 5W. It was a Sprague Koolohm P/N 5KT 15K 5W
ceramic power resistor. I have
several archival photos still showing the original Sprague resistor in place, although these components have no
date-code. The Sprague Koolohm was eventually replaced by an IRC P/N 3-8J 15K 5% 10W
“cement-block” power resistor.
- In the beginning, the
3-conductor power cable, P/N 347-4, was relatively large and black
(braid=GND, grn=key, red=B=, and yellow=6.3 Vac). Sometime later, but during the use of
the copper-plated chassis, a smaller, gray, 3-conductor cable was used
(braid=GND, white=key, red=B+, and black=6.3 Vac). I suspect this transition was around the
time that the Sprague Koolohm
was replaced by the IRC 10W
cement-block resistor.
- The VF-1’s output
voltage is specified as “10 Volts”.
Is that P-P or rms?? My
“benchmark” VF-1 has been rebuilt with a BNC connector instead of the
permanently attached RF cable. The
RF output is very sensitive to
the cable’s cap load, so I tested the output voltage with a 3’ length of 3C-2V
75 ohm coaxial cable (measured 93uuf) attached (B+ = 300 Vdc, 0A2
installed). The output voltage is
both band and frequency dependent.
On 160M, the RF output voltage varied from 5.48 Vrms to 8.31 Vrms
from 1750 KHz to 2000 KHz. On 40M,
the RF output voltage varied from 6.49 Vrms to 4.95 Vrms from 7.00 MHz to
7.3 MHz. It should be noted that
the Heathkit HG-10 VFO’s output
is specified at 5 Vrms, open-circuit,
with an RCA phono connector, and
a similar 100pf coupling-capacitor.
- The dial calibration
is tube-specific. If you replace
the 6AU6, you will need to re-calibrate the VF-1. In testing eight tubes, there was a 10
KHz spread at 7.150 KHz. I didn’t
test the end-points. In addition,
the warm-up frequency drift of the VF-1 can also be tube-specific. If you have the tubes, it’s a very good idea to select one for
the best warm-up drift.
- Speaking of tubes, conventional-wisdom
on the internet suggests replacing the 6AU6 with a 6AH6. I have tested three VF-1s with three
different 6AH6WA tubes from two different manufacturers and found that, in
all three cases, they worsen the VF-1’s warm-up drift. They also draw more power and increase
the VF-1’s internal temperature-rise.
In my opinion, it is better to test and select 6AU6s for
performance than to switch to a 6AH6.
In any event, taking the time to select either the 6AU6 or 6AH6,
for best warm-up drift, can result in some spectacular before vs after warm-up
performance. My “keeper” VF-1, that
I have had since 1991, had an original 6AU6. After testing eight 6AU6, 6AU6A, and 6AH6WA
tubes, the original tube came very close, but I replaced it with an HP-branded 6AU6A made by G.E.
Notes and References:
1.
“Heath of the Month #79 - VF-1
VFO”, by Bob Eckweiler, AF6C, 2017.
2.
“Heathkit - A Guide to the Amateur Radio
Products”, Second Edition, By Chuck Penson, WA7ZZE, 2003, page 268.
3.
“Assembling And Using Your….Heathkit Variable
Frequency Oscillator Model VF-1”, Heath Company, P/N 595-91, Copyright
1954. 20 pages not including the cover. A small 7”W x 9”L manual..
4.
During the
use of the copper-plated chassis, Heathkit
purchased a run of the P/N 40-56 6AU6 plate-coils and these were date-coded 632
- the 32nd week of 1956.
Sometime around mid-1958, Heathkit
changed the VF-1 chassis to non-copper-plated. It is interesting that a VF-1 with a
non-copper-plated chassis with a 15K 5% 10W resistor date-coded 214842, the 42nd
week of 1958, still had a P/N 40-56 date-coded 632!! That’s over 2 years from the same run!! All three of my non-copper-plated VF-1s have
had P/N 40-56 coils date-coded 632!!
And, the cans are not stamped in the same place or in the same
orientation!!!
5.
Judging by
their routine appearance on eBay, the
Heathkit VF-1 is widely
available. However, like most kits from
this era, their condition varies from very good, almost pristine, to downright
horrible!! As I write this in March of
2019, many VF-1s w/copper-plated chassis have been in the field for 65
years!!!!
Written By David W.
Ishmael - WA6VVL
- 28Feb19
Latest Revision 27Mar19