Heath SB-610 Monitor Scope Modifications

Ian A . Webb K6SDE
432 R osario Dr.
Santa Barbara, Calif. 93105
Heathkit SB-610
Monitor Scope
Modi ications
Proper optimum operation of single sideband transmitters is most easily achieved
by oscilloscope monitoring. As a result, the
H eathkit SB-61O Monitor Scope' is appearing in more and more amateur shacks as a
vital piece of equipment. As originally designed, this eq uip ment is a versatile p iece
of gear. T here arc a couple of modifications, h oweve r, that make this an even more
versatile instrument.
I will describe two modifications that I
have made to my SB-61O. Neither modification requires new front panel h oles or
mechanical changes to affect the resale value
of the SIl-6 1O. Most owners of th e SB-61O
sho u ld consider at least the first m odification. Those who have yet to acquire an
SB-610 may wis h to incorp orate the modifi cations when they construct the kit.
>< inch "hutch plug"
Lever knob"
Control knob split bush ing'
"
-----t.
Jlounting Brackett
In this mod ification, the p resen t 100 K
linear vertical ga in con trol, which is in th e
lower center of the front panel, is rep laced
wi th a 100 K linear concentric potentiometer.
A H eath kit lever knob, match ing the present
SB-6 I O knobs, is put on this new p otcntiome ter. T h is leaves a h ole throu gh the center
of th e vertical gai n control in wh ich to run
28 0 V
HORIZ.
POSlTlON
~ RY, 53000HIliIS, 4.1MA
/ II
Transmitter attenuation switch
This modificat ion moves the transmitter
attenua tion switch from its p resent p osition
in the center of th e rear a pron of th e SB610 to the Irorit panel. T he control becomes
concentric with the p resent vertical gai n
control. \ Vith the transmitter attenuation
control 011 the front panel, it is no longer
necessary to reach behind the SR-61 0 to
change the transmitting pattern height when
changing power levels or making band
changes, T his is especially useful when one
changes hands frequently or where a linear
amplifier is often switch ed on or off,
Paris required:
Concentric potentiometer element (outer
unit ) and shaft asscmblv
. , 100 K linear
(IR C-CT S CF 13 or equivalent, see text)
Potentiometer mounting bracket (Sec
F ig. 1)
Non-conducting shaft O'iG inch diameter
b y 10 inches approx.)
jr" Hf'a t hkit ~ B· 6 10 :\lo n itor
(l)('t'l'I lI!J('r ]9 (6 ), 5 4,
42
SCOllP,"
73
JI a a aZhl t ,
/'iJ, /"'"J,/
L _ - ' _....I
--'
,
•
,-
(SEE TEXT)
•
15 K (S EE TEXT )
1
, VI8
f, -- - "j ''--w_._---<.--.v.._
';];,0'
Sl-C
J /odification Schematic
the insulated shaft which controls the transmitter attenuation switch which is remounted on a new bracket facing forward ,
The choke of concen tric potentiometer is
not critical and by browsing in your local
parts house stock of replacement type conshould find a "make vour
own
trols vou
•
•
pot" selection enabling you to assemble the
"outside" portion of a dual potentiome ter.
(I used an lHC-CTS CF-13 unit with a panel
bushing about % inch long and a shaft about
" Ordt> r H vuf hkit n umbe r s 4 55 ·11 S plit Bu ahlng
$ .1 0 and ·Hi~· 19,) Lever- knob $ .5 0 ( po- tpaid) from :
H e a t h C umpnn y, Benton H arbor, Micbigan 4 9 0~3 .
13 MAGAZINE
•
% inch lon g which I cut to exactly fit the
Heathkit lever knob.)
Remove all three wires to the lugs of the
old vertical gain control (AJ in the 5B-6IO
man ual ) a nd remove the old control a nd
knobs keepin g the wires in order so the y
may be soldered to the n ew con trol. Before
mou nti ng the new pot, b e sure th at th e
knob shaft will extend just far e nough to
allow yo u to m ou nt the new lever knob on
it. Do a ny cutti ng of th e shaft b efore mounting the potentiometer to p revent d amage to
the front panel of the 5B-610. M ou nt the
new control and resolder the wires to the
corresponding lugs of the new control.
Fabricate a bracket as shown in Fig. 1
a nd refer to the p hotos to sec mounti ng
details. (If you are lucky as I was, you r
junk box will yield a su ita b le b racke t.) U nsolder th e wire fro m the coaxial connecto r
to th e lug 4 of swi tch BD, the t ra n sm itter
attenuation switch, a nd unsold er th e capacitor which run s from terminal strip G, lug
5 to term inal 5 of switch BD. You can now
remove the switch from the hack apron. If
you wish, fill the empty hole in the back
apron with a "hutch plug."
. Mount the new moun ting b racke t in line
wit h the old hole in which the switch was
mo unted. Allow eno ug h room fo r the switch
to bc re mounted b e tween th e new bracket
a nd the h ack apron. Mount the switch an d
reattach the w ire fro m the coaxial con nector
to terminal 4 and the capacitor to termin al
5 of the remounted switch . Orient the switch
so this can he accomplished with the least
difficulty. Be certain that no components stick
lip far enough to interfere with the case
when it is replaced over t he M onitor Scope.
Attach the shaft coupler to the switch
shaft a nd insert the 3/16 inch non-conductin g
shaft extens ion from the fron t pa nel into th e
hole through the vertical gain cont rol runn in g it b ack to th e shaft co upler. Ca re fully
move any parts that interfere with the shaft.
The large .25 mfd capacitor n ear the shaft
coupler between the tub e socke t (\'3) and
the terminal strip G may need to be relocated to provide suffi cie nt clearance. A metallic shaft extension is not recommended due
to the possibility of accidental contact wit h
pa rts on the chassis.
When the shaft h as b ee n properly mated,
mak e a small sh im from a piece of scrap
or tin can to red uce the ~ inch co up ler
on the sw itch to accep t the :;lg inch shaft
extension. \ Vit h the shaft in place measure
APRIL 1969
32 inch beyond the leve r knob mounted on
the vertical gain control and re move and
cut the shaft at this point. M ount the shaft
firm ly, tightening the co up ler. Use the new
split b us h ing inside the original knob removed from the vertical gain control to
fi rmly fasten the knob on to the sh aft ex ten sion Hush with th e lever kn ob.
The 5B-6IO will n ow operate exactly as
it di d origina lly. It is now p ossible to select
th e vertical gain when monitoring a received
signa l using the leve r knob a nd to change
the transmitter a ttenuat ion usin g the la rge
original knob. It is no longer necessary to
reach behind the 5B-61O each time the linear
is tu rned on or off or each time you n eed
atten ua tion changes w hen swi tching b anos.
Clamp Modification
This modification sho uld appeal to . those
p eople, m yself incl uded , who b el ieve th at
the main virtue of th e SB-610 is th e monitori ng of one's transmitted envelope usin g
the intern al sweep. If you use the interna l
Top
V i t'IV
sweep icithout also monitorin g received signals d u rin g standby periods, the trace of the
5B-6IO will re main a static baseline of h igh
intensity since the clamp circuit is inoperative in this mode. This can cause a burned
scop e face if the in tensit y is h igh enough
for good m onitorin g of p eaks in a brigh tly
illuminated room. I decided that I would
like to remove the trace from the scope face
:m loma ticalIv when th e transmitter is turned
to standby. -T his could b e d on e using the
relays tha t switch the rig from transmit to
receive, bu t since m y ri g is a transceiver
43
that I also use whe n mobile, this wo uld
involve addi tional connections to attach and
remove each time I switched from b ase station to mobile operation. Xl y modification accom plishes the clamping of the t race with
no additional connections to the transmitter
or rece iver.
Parts required:
Ca pacitor, .05 rnfd, 50 volts
Hesistors: 33K, ~ watt and resistor in
series with relay coil (see text)
Sensitive plate rela y, DPST, N. O., (Lafaye tte Radio 99H6093, DPDT, 5300 ohm,
4.1 mn ., 4 oz., shipping weight, $2.95,
Lafayette Haclio, 11 1 Jericho Turnpike,
Syosset, L.T. , N.Y. 11791 ) Sec text for
details.
The relay I used, was from my junk
box. Lackin g a suitab le relay, the one listed
in the list above is suggested. It may req uire ingenuity to moun t some relays, but
a small bit of epoxy will do wo nders if
properly applied.
Fig. 4 shows the circuit mod ifica tions to
be made. The d ark portions of the circuit
are addi tiona l components or modifications.
The clamp tube, VlB, is turn ed into a relay
amplifier. Relay contacts are used to pull
th e trace off th e screen b y shorting the
horizontal position control through a 33 K
res istor. A second set of contacts grounds
th e grid of V3A to stop the sweep. If the
sweep is not disabled, th e left portion of
the trace will still be on the screen. Pins 1
and 2 of th e front panel sweep control are
jumpered so th at the "p ull for clamp" control will work in the internal sweep position
of the sweep control as we ll as in the other
sweep positions. When this modification is
made, the SH-6IO will operate as origina lly
designed in t he RTTY and rf Trap positions
of the sweep switch. T he clamp will a lso
work in th e internal (In t.) position of th e
sweep control when the "p ull for clamp" control is pulled ou t. The d amp switch may
he pushed in so th at received signals may
also be m onitored as ori g inall y design ed.
The .2 microfarad capacitor on terminal
strip H adjacen t to tube socket VI is
cha nged to .05 microfarads to allow 1 to
2 seconds before the trace leaves th e screen.
This capacitor need not be changed, hut the
time for the trace to leave th e screen w ill
be in excess of ten seconds if it is not
changed. Remove the capacitor from str ip
H and replace it with th e .05 m fd capacitor
if you desire th is change.
44
•
Bottom View
The left hand lug of terminal strip U,
near the chassis edge was originally unused.
Remove the blue wire at pin 7 of VI and
solder it to this unused lug of terminal
str ip U. On the back of the front panel,
solder a jumper wire between lugs 1 and
" of the sweep switch.
Mount the pla te relay in the space bet ween the tube socket VI , terminal strip
U and the edge of the chassis. If your relay can he mounted with screws as could my
junk box rela y, th at is fine ; otherwise you
may have to use some ingenuity and p erhaps some epoxy to mount th e relay.
F rom one set of relay con tac ts (closed
when the relay is operated) nm a wire to a
convenient ground point such as the mounting lug of terminal strip U. From the other
contact of the set, connect the 33 K resistor
to the blue wire which you soldered to the
previously unused lug of terminal strip U
ncar the outside of the ch assis.
From the second set of contacts (also
closed when th e relay is operated) run a
w ire to ground. From the other contact of
this set. run a w ire to pin 9 of tube socke t
V3A which is the tube socket ncar the shaft
extension. This set of contac ts w ill now
ground the grid of tube V3A when the
relay is closed and stop the sweep.
Run a wire from one end of the relay
coil to the 280 volt bus. I ran the wire
to the junction of the 40 mfd capaci tor;
is K, 1 \V resistor; 1 K, J \V resistor;
and 20 mfd capa citor. This is ncar the center of the chassis on capacitor K, pin 3.
T emporarily, attac h the remainin g end
of the relay coil to pin 7 of VI through
a res istor. (T his resistor sho uld he nominally
]5 K oh ms for th e relay in th e parts list. )
The resistor should be selected so that th e
rel ay used just pulls in reliably when the
73 MAGAZINE
•
clamp sw itch is pulled out, the SB-61O turned
on, and no rf signal is ap plied . In any even t,
the plate d issipation of the 6BN8 relay amplifier should not exceed the maximum rating of 1.7 w atts. The total resistance of th e
rel ay co il plu s series resistor should be at
least 10 K. (If you use a junk b ox relay,
measure th e voltage from cathode to p late.
and the current th rou gh the t ube w hen the
relay is pulled) in. The p roduct of the voltage and current- in amperes-sho uld no t
exceed 1.7.)
T hi s completes the wiring of the modificatio n. Check the wiring against the schematic in Fig. 4. Carefully plug the SB-61O
in w ith it still ou t of the case and let it
wa rm up. Check to see if the relay opera tes
when the "p ull to clamp" switch is p ulled
out and the sweep switch is in any p osition .
If the relay d oes not opera te, first recheck
the wiring to make su re it is correct. If
the wiring is correct and th e relay will still
not pull. in, reduce th e v alue of the resistor
from the relay coil to pin 7 of VI u ntil
the relay reliably p ulls in. This will ass ure
that min imum plate dissipation occu rs in
t ube VI. \ Vhen this va lue is fou nd, solder in
the resistor permanently.
When th e "pull to clamp" switch is pushed
in, the rela y should d rop out. The tra ce
will then appear on the face of the SB-6 1O
and it should operate normally.
Set the sweep switch to Inl. and ap ply
a small amou nt of transmitter rf to the
connector at the rear of the SIl-6IO while
the "pull to clamp" switch is ou t , The relay
shou ld release and the trace should appear
to allow normal transmitted signal monitorin g. If the trace does not appea r and the
relay drop out, incr ease the rf sig nal. When
th e rf is removed by turning off th e tra nsmitter, the trace should di sappear after 1
to 2 seconds . If the trace has not moved
completely off the scope face, it may be
necessa ry to decrease the value of the 33 K
resistor. If the sweep still continues w hen
the tr ace is off screen, th e grid of t ube
V3A (pin 9) is not bei ng shorted to ground
through the relay.
I have operated my SB-6IO 24 hours a
day fo r days at a tim e and experienced
no d ifficulties. You must now remember to
tu rn off the power switch after operating,
for yo u no longer sec the green trace on
the screen to rem ind you that the 5B-6IO is
on.
. .. K6S D E
APRIL 1969
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