Pozosta SB-101, SB102 Repair

The "SB-101/SB-102 specific" information for this site is still being developed. They are pretty rugged
and Heathkit parts
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units and I've found some weak tubes, a few tubes with grid emissions, the usual requirement for
alignment per the manual, and slipping tuning dials needing adjustment. And yes, they are a poor (but
smart) man's Collins.
PURPOSE
The purpose of this Web Site is to help you bring those Heathkit SB-101 and SB-102 transceivers back to life. This information is also applicable to other tube type units. Other excellent Heathkit web sites which have SB-101 and SB-102 Service Bulletins and Fixes are:
Mark Graalman WB8JKR ... Optimizing the Heathkit HW-101, SB-100, SB-101, SB-102
Transceiver .....outstanding or backup site (same information)
Dale Wentz's excellent Heathkit support site (comprehensive information, pictures, schematics, manuals, service bulletins, etc)
Roger N4NRW .....Heathkit site with links and a downloadable master parts list
Mike Shelton, KE4LGX, Heathkit site with reproduction dials, refinished front panels (excellent),
Mike Bryce's Heathkit Repair Shop (information on many models including the SB
-
104(A))
NOTE: These are "fixes" to make the transceivers function better. If your unit does not receive, transmit,
wires which were never soldered (and are now corroded), and wrong value components installed. The
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Don Peterson's Heathkit site (parts, schematics, general info on Heath, etc)
I'm told that Heathkit always reworked units returned for servicing to the latest level, so if you have a unit serviced by Heathkit, the chances are that the fixes have been implemented but check your transceiver against the fixes on Dale Wentz's (KB9JJA) Heathkit Web Site.
etc...there is a problem that needs to be repaired ...first. Installing any "fixes" at this time would only complicate matters.
MODIFICATIONS
Some may want to replace the "Ant" RCA phono plug with a round "bulkhead" mount BNC connector. They fit nicely and provide an excellent, solid, 50 ohm antenna connection. The RCA is also an excellent 50 ohm connector system at 100 watts (better electrically than the old PL-259 UHF connector system) but after many years the ceramic insert starts to chip and deteriorate through use (compare it to the other RCA connectors). RCA connectors are not real good for mechanical retention, especially where the cables are stressed as they exit the unit. The BNC connector system is an excellent, low
power, 50 ohm system ....both electrically AND mechanically (and convenient). If you look at the
airgaps, insulator thicknesses, insulator material, and plating materials used, you will find them superior to the RCA connectors. I've never had a problem with around 100 watts, although I would not use them at 1KW. A BULKHEAD mount BNC connector does NOT modify the chassis. Remove the RCA connector and install a bulkhead BNC, which has a small threaded barrel on the back. The diameter of the threaded portion is actually smaller than the RCA connector and it mounts in the hole with plenty of room to spare.
Changing the mic connector from 2 pin to 4 pin is personal preference. Both types of connectors are readily available today from various vendors, so don't replace a 2 pin connector just because you can't find a 2-pin plug.
Asthetics: some of the knobs protrude too far, especially those with lever type dual controls. There are two versions of the level type knob, one has a set screw and the second has two tabs in the insert. The insert on the one with the set screw is recessed placing it closer to the panel. The insert on the one with
the tabs is not pressed far enough. I've cut the back of the insert down with a large drill bit ....works
great. If the lever knob on the filter selection requires too much force, lubricate the assy to prevent knob breakage, they are difficult to locate/fix. Location of the other knobs can be controlled through adjustment of the shaft bushing nuts on both sides of the panel.
BEFORE YOU START
Don't start by powering the unit up as your first step. Something could have been knocked loose due to shipping/transport. Also, since these are kits, don't automatically assume they worked at one (or any) time. I can't stress this last point enough because it's not usually part of commercial receiver debug. I have found missing components, incorrectly installed components, solder blobs shorting board traces,
point is, don't automatically assume a complex kit is wired correctly even if you were told "worked great
the last time I used it" by the previous owner/seller.
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SPECIFIC REPAIR INFORMATION
TBD
1. Receiver Sensitivity
SB-102 receiver sections have fairly good sensitivity through the use of low noise 6HS6 tubes.
The same can be applied to SB-101 receiver sections. More later with backup data.......
Chart showing dBm-power-microvolts for a 50 ohm receiver input
dBm power microvolts (rms)
-134.9 3.2E-17 0.040
-133.0 5.0E-17 0.050
-131.4 7.2E-17 0.060
-130.1 9.8E-17 0.070
-128.9 1.3E-16 0.080
-127.9 1.6E-16 0.090
-126.2 2.4E-16 0.110
-125.4 2.9E-16 0.120
-124.1 3.9E-16 0.140
-122.9 5.1E-16 0.160
-121.9 6.5E-16 0.180
-121.0 8.0E-16 0.200
-120.1 9.7E-16 0.220
-119.0 1.3E-15 0.250
-118.0 1.6E-15 0.280
-116.9 2.0E-15 0.320
-115.9 2.6E-15 0.360
-114.9 3.2E-15 0.400
-114.1 3.9E-15 0.440
-113.0 5.0E-15 0.500
-112.0 6.3E-15 0.560
-111.0 7.9E-15 0.630
-110.0 1.0E-14 0.710
-109.0 1.2E-14 0.790
-108.0 1.6E-14 0.890
and USB in a quiet section of the band (no antenna). If you hear a difference in signal, they are not
meter. The high level signal output is the separate output for a
frequency counter, monitor, etc ....not the output that comes out of the attenuator. Pull the "Mode"
Heathkit 404
-
283 SSB Filter 2.2Khz at
-
6dB, CF 3395.10KHz, 2.5dB ripple
-107.0 2.0E-14 1.000
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2. IF Filter Passbands
One of the problems I encountered on a SB-104A, and it applies here also, was that the IF filter passband shifted, reducing full output when using USB. The Heathkit SSB filter BW on these SB­xxx units (as well as Collins KWM-2s) is specified as 2.1KHz at 6dB down. Heathkit separates LSB and USB by 2.8KHz which means USB and LSB are both 1.4KHz on either side of the filter center frequency. For a 3395.0KHz filter that means 3396.4KHz for USB and 3393.6KHz for LSB. Just for comparison, the Collins LSB/USB signals are separated by 2.7KHz, or 1.35KHZ on either side of their center frequency.
IF Passband problems can also occur if the LSB/USB crystal frequencies move relative to the filter center frequency and side slopes. A quick check is to switch back and forth between LSB
both equally positioned on the opposite filter side slopes. A better approach is to measure the oscillator frequencies with a frequency counter but you still need to know what your IF filter center frequency is.
You can "see" the IF passband by injecting a 3395.0KHz +/-3KHz high level CW signal from a signal generator and watching the S-
oscilator tube for this measurement. Very sloooowly tune the signal generator through the IF passband and note the frequencies where you have a reading of "S1". This will give you a rough idea of the passband but most signal generators don't tune slowly enough, have bothersome backlash, and require a calibrated frequency counter. If you detected several dips using the S­meter, that's right, see filter profiles below.
If you really want to see what the IF passband looks like you must use a spectrum analyzer with tracking generator. Below are two random examples of filters tested in a fixture with impedance matching transformers and correct filter termination resistors. A ripple of 3dB or less is considered acceptable (the less ripple, the better). The horizontal scale is 500Hz/Div, the vertical scale is 1dB/Div, and the bright line is the cursor set at 3395.00KHz):
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