To further reduce costs, the HW came with one 10m segment Khz and had a "full 10m coverage" option. The SBA came out in , was produced until , and is a much improved design version of the SB incorporating most of the available critical fixes. NOTE: These are "fixes" to make the transceivers function better. If your unit does not receive, transmit, display, etc

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To further reduce costs, the HW came with one 10m segment Khz and had a "full 10m coverage" option. The SBA came out in , was produced until , and is a much improved design version of the SB incorporating most of the available critical fixes. NOTE: These are "fixes" to make the transceivers function better.

If your unit does not receive, transmit, display, etc Installing any "fixes" at this time would only complicate matters. Very often you see SB A s and other older transceivers advertised as "not working", "has low output", as "parts only" radios, or see them on e-Bay with "works great" and " These are generally simple problems to fix.

Most of the time it was out of alignment, some other cheap component was defective, a bad solder joint, etc. Besides, "IF" the finals are bad they can be replaced with similar components which are more readily available today. Some were published as late as , which demonstrates how "Fellow Greenies" want to keep these rigs on the air. With a "nibbler" tool you can enlarge the hole slightly and mount a socket. They fit nicely and provide an excellent, solid, 50 ohm antenna connection.

The RCA is also an excellent 50 ohm connector system at watts better electrically than the old PL 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 The only drawback is power handling capability, but if you look at the airgaps, insulator thicknesses, insulator material, and plating materials used, you will find them superior.

Remove the RCA connector and install a bulkhead BNC, which has a small threaded barrel on the back, with the nut provided. The diameter of the threaded portion is actually smaller than the RCA connector and it goes through the hole with plenty of room to spare. Changing the mic connector from 2 pin to 4 pin is personal preference.

A schematic for the particular transceiver you have is mandatory, as is the Operations Manual. The Assembly Manual is not required but you may find it useful. An extender card, or some other means of gaining access to probe points on the cards, is also mandatory. This is also useful since it puts the boards in their operating environment since use of the extender card can cause oscillations due to unshielded coupling to other boards and the longer lead lengths.

In particular, this can be seen when board C is on an extender or when two boards F and H, F and G are on extenders. The mechanical meter is required to dampen out fluctuations for accurate adjustment.

Another great tool is a "cheapo" 2K ohms per volt VOM for checking diodes and transistors. Most of the suspect transistors and diodes can be readily pulled for measurement. For the PA transistors, the easiest method is to cut the appropriate trace s with an X-acto knife, make the measurements, and resolder the trace. Many of these devices are paralleled with other components and can not be tested "in place".

I have found missing components, incorrectly installed components, solder blobs shorting board traces, and wrong value components installed Pins 7, 8, 9, 10 are negative ground. Pins 11, 1, 2, 3 bring positive Pin 4 brings There have been "Transmit does not work" problems reported because only pin 4 was wired to Pins 5 and 6 are used to switch power on and off in the power supply if your external supply is so equiped.

The Heathkit SB A supply is so equiped. A visual inspection and cleaning is a good place to start. You may also find it useful to bend one or more of the three small spring fingers on each contact a little to make more reliable contact with the chassis mounted pins. The pins oxidize over time and I have seen the pins coated with grease to reduce oxidation. There will definitely be a variation from unit to unit depending on the fixes installed and they should be used as guidelines. If you expect to see mv and see mv, no problem.

On the other hand, if you see 10mv, there is a problem. Relative to the schematic: RF measurements are taken with a RF probe simple to build, check the ARRL Handbook , p-p peak to peak measurements are taken with an oscilloscope. The "Tune" position is for adjusting the antenna tuner, etc and for QRP operation before applying full power.

Let me state at this point to NOT "rig something up" for the connector. SB A s do NOT have reverse voltage protection usually a large diode which is normally reverse biased like some other units have. If you momentarily reverse the power you will probably take out the regulators and Q on the "G" board A protection diode is a good item to add to your SB A. Computer manufacturers discovered that a long time ago. But this is the home environment, down time is not mission critical, and some can not afford the cost of board level replacement.

Someone is going to have to debug those bad boards There is a sequence to debug which seems to work best: check power first and recheck it at every card being debugged, then get the receiver to work starting with any noise from the speaker and working back to the antenna, then work on the transmitter starting at the VFO and work toward the antenna.

When I powered on my first SBA all that happened was the 2 pilot lights came on and the meter would read No display, no noise, no Tx relay picking, no S-meter reading, nothing But, on the other hand, no excessive current draw or smoke Several of the "needs work" SBs say that they have "low power output" with an implication that the PA "H" board transistors may be fried.

Intermittent problems can often be traced to defective solder joints. When in doubt, reheat the joint and apply a little solder. If there is a large qty of solder already, wick it off or use a "solder sucker" and renew it.

Grounds signal return paths as well as shielding are as important as the signal wiring and all ground points should be examined to make sure they make good electrical contact. The card side rails are important for proper operation and the minimizing of spurious signals. Some boards have been removed so often they have worn through the solder covered traces on the sides.

I have added copper tape to these boards to maintain electrical contact. Also check any mounting screws for good contact on the Noise Blanker card, Driver board, etc. The later SBAs used film resistors shiny, "dog bone" shaped which are typically more stable over time than the older composition resistors dull, cylindrical.

Many of the older composition resistors, through age and moisture intrusion, will change value so check when they are suspect Stiff tuning can often be fixed by relubricating the ball vernier drives. Even the Jackson Bros vernier drives especially old ones develop something other than smooth tuning due to hardened lubricant, dirt, dust, etc feel a slight grinding, backlash, etc. Too tight will result in stiff tuning, too loose will result in slipping. But it does allow you to completely clean the drive assembly.

Soaking in solvent works to some degree. A much easier way, which works well, is to heat the body of the vernier with your soldering iron reflows the grease. If you need more grease use automotive lithium chassis grease or Lubriplate. Intermittent potentiometers or those with "stiff" adjustment can often be fixed by spraying with a little DeoxIT CAIG Labs or in the case of stiff adjustment, also remove the knob and spray the bushing. Same goes for switches, plugs, sockets, etc. Check the voltages at the "B" board and the pass transistors.

These regulators are somewhat difficult to find but there are alternatives. If you have exhausted parts sources for the original MFC, you might try substituting the UA78MG or take a more drastic step of redesigning the regulator circuit. I wanted adjustment capability so, replaced the on board regulators with LM units and redesigned the circuit to use PNP pass transistors and multi-turn adjustment potentiometers on the top of the "B" Board.

You can use the existing NPN pass transistors, but you loose control over the voltage drop across the pass transistor NOTE: Always set up the adjustable voltage regulator board for correct output on the bench A second SBA showed 6, Also no audio. The short burned through the negative lead on C6 and the surges probably took out the regulator. A defective Q which allows 5 or 6 volts on pin 6 of the "B" board in receive mode, will effectively bias the audio off pin 7 of the "F" board.

There are suggested substitutions for this PNP transistor 2N, etc or you might go with a higher current substitute like a Radio Shack transistor as indicated in the N2EO article and reduce the value of R from 4. Make sure the spring fingers over the 10m coils make good contact with the metal partitions. Check the band select switching levels for proper individual switching. If not correct due to a solder bridge, for example you may have multiple tuned circuits selected simultaneously.

If you need to replace one, use a common 1N Do not use 1Ns for any of the mixers or any signal diodes. One diode D was intermittent. Apparently one lead had actually come loose in the glass. The Input voltage pin 3 should be. The injection level pin 10 should be around. The 15m and 20m filter sections on the SB were wider. On the SBA, they were narrowed to reduce spurs but this required tuning of the filters to provide adequate levels across the entire band.

For 15m, the change was: C a 3. For 20m, the change was C a pf?


Heathkit Schematic and Manual Archive

The original gas discharge displays as well as the high voltage decoder IC are past their prime. Remember, this new display board will not fix a problem caused by a bad "A" card. This kit replaces the gas discharge display with solid state LEDs. There was nothing like it on the market. Even commercial transceivers lacked a digital display. Now that the SB is approaching over 30 years old, most of those display tubes are not longer as bright as they use to be. So what goes wrong?


Heathkit SV-104A Operation Manual


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