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Heath of the Month #84 - V-6 VTVM Restoration Part 1
Heathkit of the Month #84:
by Bob Eckweiler, AF6C
KIT RESTORATION:
Heathkit V-6 VTVM Restoration Part I
“Siliconizing” the V-6 Selenium Rectifier
(Heathkit part # 57-1, Sarkes Tarzian Model 35)
Introduction:
I didn’t think I’d have a Heathkit article this
month. However, while awaiting parts to arrive I decided to see if I could convert the
#57-1 selenium rectifier to silicon (See figure
1) in the V-6 VTVM under restoration. It
presented a bit of a challenge and one I was
happy to undertake slowly, whenever I needed a break from the less exciting task of doing taxes. Now, all the parts I believe I need
have arrived save one (one vendor sent me the
wrong part and is resending a correct one).
Currently the rebuild of the V-6 is coming
along slowly, mostly due to the lack of parts
and a lot of other obligations. However, the
preliminary wiring of the chassis assembly is
finished, and the assembly and wiring of the
front panel is in progress. Still to do, before
mating the two, is the teardown, cleaning
and lubrication of the function switch, and
the cleaning and lubrication of the the range
switch. The precision resistors remain attached to the range switch since they are
hard to replace and delicate. One resistor is
open, but a replacement is finally on hand.
After that, assembly can be completed and
testing and calibration can begin.
The Selenium Rectifier:
The power supply in the early Heathkit
VTVMs uses different forms of rectification
as the models progress. The V-1 and V-2 use
a 6X5 dual diode vacuum tube. The V-3 is
battery powered (though whether any were
sold is in question). The V-4(A)* uses a selenium rectifier (part # V97) which is a green
commercial multi-plate rectifier similar to the
one shown in figure 2. The V-5(A), and V-6
use a small Sarkes Tarzian Model 35 selenium rectifier (Heathkit part # V123, renumbered 57-1 in their revamped parts numbering system). Finally Heathkit settled on a
sealed, small and inexpensive selenium rectifier in the V-7(A) (part # 57-13), also manufactured by Sarkes-Tarzian (Model 50); it is
rated for 130 vac and 50 ma. In 1963 it sold in
single quantities for 48¢; likely, significantly
less at Heathkit quantities.
Copyright 2008 - 2018, R. Eckweiler & OCARC, Inc.
Page ! of !1 4
Here is a link to the index of Heathkit of the
Month (HotM) articles:
http://www.w6ze.org/Heathkit/Heathkit_Index.html
Figure 1: Heathkit #57-1 Selenium Rectifier.
(Sarkes Tarzian Model 35)
* Note: When a Heathkit model number is
shown with one or more letters after it in
parentheses it refers to multiple kits. Thus:
V-4(A) refers to V-4 and V-4A.
HP-23(A)(B)(C) refers to HP-23, HP-23A
HP-23B and HP-23C
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Heath of the Month #84 - V-6 VTVM Restoration Part 1
Selenium rectifiers tend to deteriorate over
time according to many sources. And though
I’ve never had a failure nor felt the need to
replace one of the later sealed #57-13 rectifiers, the unsealed #57-1 worried me. The
simple solution is to remove the rectifier,
mount a Cinch 810 terminal strip in the hole
where the rectifier mounted, and solder a
1N4004 diode across the two terminals of the
terminal strip. However, this reduces the authenticity of the restoration. It would be better to convert the selenium rectifier to silicon, and keep its form factor.
An examination of the 57-1 rectifier shows it is
held together with a spring clip and easily disassembled into a phenolic housing, two phenolic end plates, two terminal end plates and a
stack of selenium-coated plates (figure 3).
The selenium plates were wrapped and discarded as toxic waste. Selenium, in excess, is
toxic so wash your hands well when you are
done. Next, the two metal terminal end pieces
were cleaned and a small hole drilled in the
center of the large rectangular section of
each plate. (a #55 drill - 0.052” dia. was used).
The area around the holes were tinned on one
side, The leads of a 1N4004 diode we're also
tinned. The cathode end of the diode was then
soldered through the hole in one terminal end
plate (tinned side towards the diode cathode),
and the lead trimmed flush to the plate. This
cathode terminal should be marked as such
with a felt-tip marker.
A 1/2” diameter phenolic spacer, about 0.325”
in length, was found in the junk box It just
barely wouldn’t slip into the phenolic case
until four flats were ground 90° apart around
the spacer. One phenolic end plate and the
terminal end plate with the diode attached
Copyright 2008 - 2018, R. Eckweiler & OCARC, Inc.
Page ! of !2 4
Figure 2: Selenium rectifier similar to the
Heathkit V97 rectifier.
Figure 3: The disassembled 57-1 Rectifier.
1. Phenolic case 3. Terminal End plates
2. Phenolic end plates 4. Selenium coated plates
Not shown - Spring clamp with mounting tab (#5 in figure 4)
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Heath of the Month #84 - V-6 VTVM Restoration Part 1
were slid into the phenolic case. The spacer
was then slid over the diode and the second
terminal end plate was pressed flush to the
phenolic spacer and soldered. If the diode
lead was already tinned along with the side
of the terminal end plate that is towards the
diode, the solder should be drawn into the
hole with little solder remaining on the outer
side. This diode lead is then also cut off flush
to the terminal end plate. Finally the second
phenolic end plate is placed above the top
terminal plate and the whole assembly is
Copyright 2008 - 2018, R. Eckweiler & OCARC, Inc.
Page ! of !3 4
Figure 4: Beginning Reassembly
1. Phenolic case
2. Phenolic end plates
3A. Drilled terminal end plate
3B. Terminal end plate with diode
5. Spring clip with mounting tab
6. Phenolic spacer
Figure 5: Partial Reassembly.
3A. Drilled terminal end plate.
5. Spring clip with mounting tab
7. Assembly of:
a. A phenolic end plate
b. A end terminal plate with diode soldered on
c. Phenolic case
d Phenolic spacer
Figure 6: Ready for Final Assembly
1. Phenolic case (slot up)
2. Phenolic end plate
8. Assembly of:
a. two terminal end plates
b. phenolic spacer
c 1N4004 diode (or equivalent)
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Heath of the Month #84 - V-6 VTVM Restoration Part 1
placed into the spring clip with mounting
tab. This has to be assembled so the cathode
terminal end, with its lug pointing up, is towards you when the mounting clip is pointed
to the right (See figures 4, 5, 6 and 7).
The result is a silicon 1N4004 rectifier diode
mounted inside the case of the #57-1 selenium rectifier case. This diode should outlast
the V-6 VTVM.
Comments:
Usually I try to write about an unusual kit
for the April issue. There was the Heathkit
mahogany candlestick (my favorite), the
Heathkit “freebee” flashlight. Once I even
published a writeup of an imaginary kit, the
Heathkit C-7 Lakota. Needless to say the author was a historian of General Custer. Other unusual Heathkits that were covered in
the April issues are a log splitter, a garbage
compactor, a $6,000+ 15 lb. 386 based laptop
computer, and a motorbike. I hope this article is esoteric enough to fit in.
Ten Year Anniversary:!
Can you believe that it was ten years ago this
past February that the first Heathkit of the
Month article appeared in the Orange County
Amateur Radio Club newsletter RF ! In those
ten years there have been 84 feature articles
including this one, and a few short articles.
That amounts to over eight articles each year.
No, it’s not exactly accurate to call the series
Heathkit of the Month, but’s close enough that
I don’t have any guilt feelings. That first article covered the GR-121 Clock Radio that followed me through my college days.
The New Heathkit:
It’s been some time since the new Heathkit
started operations. The current kits they offer are a TRF AM Radio (in soldered and solder-less versions), a Stealth 2m/0.75m antenna, a Digital Clock, and a Precision RF
meter (for which Heath is currently accepting preorders). They also have some neat accessories, updates and replacement parts for
various legacy Heathkits such as the
AJ-1510(A) tuner, the HG10(B) VFO, the IG18 audio generator, and some replacement
parts for the weather stations. You might
want to checkout their website at:
www.heathkit.com
Their GC-1006 “Most Reliable Clock” sells for
$99.95 which some feel is expensive for a digital clock. However, in 1990 dollars that is $52.
Hopefully the new Heathkit will release some
ham related kits that will draw the new generation of hams back into kit building.
73, from AF6C
Copyright 2008 - 2018, R. Eckweiler & OCARC, Inc.
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This article originally appeared in the
April 2018 issue of RF, the newsletter of the
Orange County Amateur Radio Club - W6ZE.
Remember, if you are getting rid of any
old Heathkit Manuals or Catalogs, please
pass them along to me for my research.
Thanks - AF6C
Figure 7: Completed Selenium Rectifier
Converted to Silicon with Cathode Marked
Prior to installation in the V-6, the ‘K’ was cleaned off
with alcohol, but the red marking on the cathode
terminal stem was left on.
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Heath of the Month #86 - V-6 VTVM Restoration
Heathkit of the Month #86:
by Bob Eckweiler, AF6C
KIT RESTORATION
Heathkit V-6
VTVM Restoration Part II.
Introduction:
It seems like this project took forever to
complete, though actual time working on it
was not many hours over a long period. Part
I appeared in the April 2018 issue of RF
and covered “siliconizing the selenium rectifier” in the V-6. This amounts to removing
the selenium plates and replacing them with
a silicon diode (a 1N4004 here) while keeping
the outside appearance of the original part.
The restored Heathkit V-6 VTVM (circa 1952
to 1954) is shown in Figures 1 and 2 during
burn-in. Figure 15 shows the V-6 schematic.
If this project were to be done over, there are
a few things that should have done that
weren’t. The first is taking photos of the original V-6. When the cover first was removed a
disaster was revealed and the plan changed
to recover any parts and take the rest to the
electronic scrap yard. Like most all VTVMs
the Heathkit V-6 uses a battery for its ohmmeter circuit, a 1.5 volt ‘C’ battery. The battery was no longer in the unit but the damage it had done from leaking was extensive.
Two of the three metal chassis parts were
corroded significantly and the third less so,
but still damaged. The almost “unobtanium”
7.5 Meg Ω potentiometer in the A.C. balance
circuit was badly corroded. So much so that
removing it resulted in the threaded bushing
disintegrating. Amazingly the pot element
appeared okay. After reading a discussion1
on cleaning and restoring a chassis, the decision was made to try a restore despite the
damage.
The second thing that should have been done
was to check and clean the OFF-ON slide
switch. This was an oversight; a fair amount
of time was spent cleaning the two rotary
switches, actually disassembling one. The
OFF-ON switch however, when removed from
the chassis, had its terminals cleaned of excess solder and put in the box of parts with-
Copyright 2008 - 2017, R. Eckweiler & OCARC, Inc.
Page ! of !1 12
Figure 1: Completed restoration of the Heathkit V-6
VTVM during burn-in. The slight meter offset is inten-
tional and indicates the circuit continues to function.
Here is a link to the index of Heathkit of the
Month (HotM) articles:
http://www.w6ze.org/Heathkit/Heathkit_Index.html
1
Notes are on page **.
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