Heathkit Service Bulletins - SB-221 (Updated & Complete)
Joseph W Lutz
joelutz at JUNO.COM
Sat Jan 10 12:05:25 EST 1998
November 28, 1978
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-1
New Tuning
Capacitor
A new tuning capacitor [PN 26-164] will be available after January of
1979. This capacitor has a higher breakdown voltage.
The first two productions will not have this capacitor. After the part
becomes available, the tuning capacitor, C55, should be replaced with the
new type only upon customer complaint of arc-over.
---------------------------------------------------------------------------------------------------------------
February 20, 1979
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-2
Tuning Capacitor Arc-over
A new tuning capacitor, C55 [PN 26-164] is now available which has a
higher breakdown voltage to prevent arc-over problems.
The first two productions will have a [PN 26-131] capacitor installed/
These tuning capacitors should be replaced with the new type if arc-over
is a problem.
The new tuning capacitor is about 1-1/2" longer than the older one, so it
is necessary to install a space at "DA" to permit proper mounting of the
plate coil. Install the space as shown in the pictorial. (((Spacer is
attaced to coil at the plate coil bracket))).
Parts required:
1 - 6-32 X 1/4" screw [PN 250-56]
1 - #6 lockwasher [PN 254-1]
1 - 6-32 X 1-1/2" tapped metal spacer [PN 255-129]
1 - capacitor [PN 26-164]
This bulletin supercedes SB-221-1 dated November 28, 1978.
--------------------------------------------------------------------------------------------------------------------
May 15, 1979
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-3
Sheet Metal Screws Will Not Tighten
If the perforated covers will not secure properly due to enlarged sheet
metal holes, install a 6-32 speednut [PN 252-22] over the lip and
surrounding hold. The 6-32 X 3/8" sheet metal screw [PN 250-8] will then
tighten securely.
Using the speednuts does not noticeable degrade the products' shielding
capabilities.
--------------------------------------------------------------------------------------------------------------------
January 21, 1980
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-4
Linear's Relay Damages ICOM-701's
++++Information not available at this time++++
-------------------------------------------------------------------------------------------------------------------
January 21, 1980
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-5
Apparent Self-Oscillation When Used with Kenwood Transceivers
++++Information not available at this time++++
------------------------------------------------------------------------------------------------------------------
March 7, 1980
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-6
Interfacing The Linear To Kenwood Exciters
++++Information not available at this time++++
-------------------------------------------------------------------------------------------------------------------
September 2, 1980
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-7
RFC 6 Overheats And Circuit Breakers Trip
++++Information not available at this time++++
------------------------------------------------------------------------------------------------------------------
January 30, 1981
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-8
Conversion For 10-Meter Operation
++++Information not available at this time++++
------------------------------------------------------------------------------------------------------------------
February 25, 1982
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-9
Schematic Correction - Incorrect Location For CB1 and CB2
++++Information not available at this time++++
------------------------------------------------------------------------------------------------------------------
November 22, 1982
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-10
Part Number Corrections - Plug And Socket Shells
++++Information not available at this time++++
-----------------------------------------------------------------------------------------------------------------
November 30, 1982
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-11
Breakdown Of C56
[[See SB-221-12]]
++++Information not available at this time++++
------------------------------------------------------------------------------------------------------------------
June 13, 1983
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-12
PN 21-792 For C56 Not Available
[[Supercedes SB-221-11]]
++++Information not available at this time++++
-------------------------------------------------------------------------------------------------------------------
April 6, 1984
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-13
Interfacing The Linear To Kenwood Exciters
The ALC voltage to Kenwood transceivers and transmitters should not
exceed -8 volts. To Ensure the proper voltage to the Kenwood, add:
An 8 volt zener diode [PN 56-621] across the ALC connector onthe back of
the amplifier. Connect the banded end of the diode to the ground lug.
Adding a control in the ALC line (as instructed in previous bulletins) to
control the level of ALC voltage doesn't always work. This control loads
the ALC line so much that very little ALC voltage is developed, resulting
in the exiter overdriving the linear, In units which have the control
installed and the operation is still unsatisfactory, return the ALC
circuit to its original design and install the zener diode.
------------------------------------------------------------------------------------------------------------------
April 26, 1985
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-14
T2 Overheats And Fails When Operating On 220 Volt Line
When the linear amplifier is wired for 220 volt AC line operation, and
the contacts on SW2 [PN 61-45] or a high voltage transformer winding
opens, excessive current will flow through the primary of low voltage
transformer T2 [PN 54-238],
causing it to fail. To prevent this failure, the black-green lead and
the black-yellow lead of T2 are lifted and connected together with a wire
nut.
To do this, refer to the drawing at the right and remove the black-green
lead at lug 3 of terminal strip AE [the lead from T2 at grommet AK] and
the black-yellow lead at lug 2 of SW2. Connect these wires together with
a wire nut [PN 432-199].
Make this wiring change on units you receive for service which are wired
for 220 volt AC operation. Let the customer know that this wiring change
has been made. If he wants to operate on 120 volts AC, he'll have to
reconnect these wires as shown in the assembly manual.
-------------------------------------------------------------------------------------------------------------------
October 25, 1985
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-15
PN 21-79 Capacitor at C7 Unavailable
The .001 uF, 6000 volt ceramic capacitor used at C7 is not available from
our vendors. Until an exact replacement capacitor is obtained from other
sources, two 5000 pF, 3000 volt ceramic capacitors [PN 21-116] will be
connected in series at C7. A bulletin will be issued to notify you when
the [PN 21-79] capacitors are once again available.
--------------------------------------------------------------------------------------------------------------------
December 23, 1986
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-16
L5 Mounting Clip Won't Fit Hole In Coil Shield
Panel
The 80 meter input coil [PN 40-1012] at L5 now supplied by our vendor has
a coil clip that is too large in diameter to fit the mounting hole in the
coil shield panel. The coil clip on the new coil is .417" in diameter;
the old clip is .406" in diameter. This difference is less than 1/64 of
an inch. The .406" diameter clip is no longer being manufactured.
The new coil can be installed in either of two ways:
1) Remove the coil clip from the old coil being replaced and use this
clip to replace
the clip on the new coil. The old and new coils have the same
diameter coil form.
2) If the old clip isn't available, enlarge the mounting hole in the
coil shield panel
about 1/64" larger in diameter.
When the new [PN 40-1012] coils are placed in Parts Replacement stock,
customers who order the new coil will also be sent an instruction sheet
[PN 597-4650] to tell them to use the clip from the old coil or to
enlarge the mounting hole.
--------------------------------------------------------------------------------------------------------------------
January 16, 1987
SB-221 Bulletin No:
2 KW Linear Amplifier SB-221-17
ICOM Transmitter Anternna Relay Contacts Fail When Connected
To Antenna Relay Jack On Heath Linear Ampliers
The 120 VDC at the Linear Amplifier antenna jack exceeds the 24 VDC
maximum rating of the antenna relay contacts in the ICOM transmitter.
This excess voltage causes the relay contacts in the ICOM transmitter to
weld together. To prevent this, connect the ICOM transmitter to the
Linear Amplifier using a 12 VDC as shown in the drawing below.
. \.______>Ant Relay Heath
|________> Jack
Linear
ICOM>_________________
Amplifier relay 3 +12v
jack <____ 3 Coil
| 3
+12 V |
| |
GND GND
((Sorry for the poor drawing - just another reason to get the scanner
working))
A relay box for this purpose is available for ICOM America, Inc.
-----------------------------------------------------------------------------------------------------------------
Thats everything I hold up to 1989 that covers the SB-221 . Enjoy!
-----------------------------------------------------------------------------------------------------------------
73 de Joe W7LPF/4 [NNN0KUU]
QWCA - SOWP - NCVA - FISTS - RCC
Gordonsville, Va 22942 [Orange Co]
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