NoobowSystems Lab.

Radio Restoration Projects

SideBand Engineers Model 34
SBE "SB-34"

Bilateral Amateur Radio Transceiver

Japanese Page

SB-34 Prototype

SideBand Engineers - The Company


    SideBand Engineers SB-34 is a HF SSB transceiver, arrived on market in 1966. Considerable numbers manufactured, this radio could be classified as "interesting radio" for most of the amateurs; although quite charm and was indeed popular, it is not well regarded in comparison to the big stars such as Collins, Hallicrafters or Drake. However, if you become familiar with its design and construction, you will be amazed with this advanced, ambitious radio.

    The configuration of SB-34 is almost identical to its predecessor, SB-33, but its style is much more sophisticated.
    SB-34 is fully transistorized except transmitter driver and final amplifier. It has a built-in power supply which is capable to run both on AC117V and DC12V (SB-33 required external inverter in order to run from DC12V). Compact body archived by the transistorization is suitable for the mobile operation. The transceiver only handles SSB, and covers 3.8/7/14/21 MHz bands. Output transmit power is claimed to be 80W.
    SB-34 employs a Collins mechanical filter, and has a "bilateral" circuit configuration. Block Diagram shows how the bilateral works - signal flows in opposite direction when transmitting, than when receiving. It made possible to reduce total number of components, thus the compact, lightweight and lower priced rig.


    So let's take a look at the SB-34's front panel. By comparing to SB-33, you'll find its basic arrangement is kept. I guess the mobile use would be in mind in this arrangement; frequently used controls were located at the left side of the panel so that the operator could reach them easily when the transceiver was mounted at the passenger under-dash.

Tuning (VFO)

    The dial and a knob at the upper left is the VFO, controls the transmission and reception frequency. The knob and the dial is concentrically located. A coaxial reduction shaft possibly made by Jackson Brothers (if not, similar) drives a compact, 3 section gang tuning capacitor. The reduction shaft features double speed; the reduction ratio is high within range of three-quarter rotation of the knob. By rotating the knob more than that, the reduction ratio automatically becomes low so that the quick frequency change can be made. The dial is illuminated by a small lamp from inside.
    Frequency coverage is as follows.
  • 80M :  3.775MHz - 4.025MHz
  • 40M :  7.050MHz - 7.300MHz
  • 20M : 14.100MHz - 14.350MHz
  • 15M : 21.200MHz - 21.450MHz


    The knob located at the center of the front panel is the band selector. Can be rotated approx. 330 degrees, this control changes the band, and tunes the RF stage. Internal mechanism consists of a reduction gear and cam called "Geneva Mechanism". It rotates a 3 section tuning capacitor, rotates a rotary switch for band selection, and alters the slug core position of the 3 tuning coils.


    The meter at the top center of the panel only works when transmitting. It indicates plate current of the final tubes, or relative RF output level. The scale has numbers from 0 to 5; no exact value of the plate current could be known. Biggest disadvantage of this rig is that there is no S meter. Everybody would ask why this meter does not work while receiving. The reason lies in its unique AGC design. No illumination is provided for this meter.


    This knob slightly varies the Tx/Rx frequency. By adjusting this knob, the main dial can be calibrated to the best accuracy. To do this, receive a signal with known frequency or use the crystal marker which was provided as genuine option unit.


    Adjusts the microphone gain. No AGC is provided in the microphone amplifier in this transmitter, therefore attention must be paid to the overmodulation. The operation manual suggests the user to get signal reports from other stations, so that the best mike gain could be found for the operator's voice and mike characteristics.


    While it looks pretty normal, this volume control is actually quite unique. It controls RF gain, IF gain and slight amount of AF gain. It controls the AGC characteristic as well.


    When the PITCH switch is set to ON, the PITCH knob slightly varies the reception frequency. In short it is a RIT.


    Selects the USB or LSB. No CW mode is provided.


    When turned ON, the crystal calibrator unit attached to the back panel starts oscillation. It is actually a simple switch turns on/off the power supply to the external calibrator unit. The calibrator unit was genuine option. This unit does not have one.


    When this switch is ON, heaters of the vacuum tubes are energized. By turning off this switch, current drain drops to approx. 600mA so that the car battery can be saved greatly for the receive-only operation. When the rig is running from AC117V, tube heaters are always energized regardless of the switch position.


    By setting this to TUNE, continuous carrier is generated so that the final tank circuit could be easily tuned.
    Microphone jack is located at the dead center. It accepts the Collins type microphone plug.


    The load of the final tank circuit can be tuned.


    This switch selects the function of the meter while transmitting. RF output power can be monitored when switched to ANT; plate current of the output (final) amplifier can be checked when set to Ip.


    Tunes the final tank circuit. This adjustment should also be made while reception.


    Let's take a look at the inside of the radio. Outer case is one piece sleeve. Basic construction is steel frame style carrying several print circuit boards.

Circuit Description

    Block diagram here shows its unique bilateral configuration. Yellow blocks are used both in reception and transmission.
    There are 2 keying control buses. While receiving, the voltage of one bus is high and the other is low. When transmitting, voltage level of buses are swapped. One bus is used to disable the Tx only blocks while receiving, the other disables the Rx only blocks while transmitting. Keying is done in such manner, successfully eliminated the mechanical relay.

RF Amplifier

    The incoming signal from the antenna terminal goes through the transmitter pi-match section, and enters into the tuner board located at the bottom side of the chassis. Two diodes protects the front end devices against the overloading. Signal is fed into the emitter of the RF amplifier transistor, Q11. This transistor works as common-base amplifier.

HF Mixer

    Amplified signal is fed into the HF mixer, consists of Q9 and Q10. Meantime a HF crystal oscillator Q19 generates the local frequency fixed to each band. The HF mixer converts the incoming signal to 1st IF, ranging from 3175 to 3425kHz.

    The Picture here shows the crystal board, located at the bottom side of the chassis. It carries 4 HF oscillator crystals for each band and a transistor Q19 (hidden).

VFO Nixer

    The HF mixer output exits the tuner board and enters the VFO board, and fed to the VFO mixer transistor Q7 and Q8. VFO oscillator Q15 generates the signal ranging from 5456.9 to 5706.9kHz depending on the VFO dial knob position. The VFO output is buffered by VFO buffer Q14, and fed to the VFO mixer.
    As a result of heterodyne processing, 2nd IF of 2281.9kHz is obtained, which frequency is the difference of 1st IF and VFO frequency.

IF Mixer

    The 2nd IF signal, 2281.9kHz, exits the VFO board and goes through the mixer diode then enters the IF board. On the IF board there is a reference frequency generator. It has a 456kHz crystal carrier oscillator Q12, followed by a doubler and doubler/trippler Q13. When the mode switch is set to USB, the reference generator gives the 2738.2kHz (6 times of 456kHz), or 1825.5kHz (4 times of 456kHz) for the LSB position.
    This reference frequency is added to the mixer diode. As a result of mixing the reference frequency and 2nd IF, 456.38kHz 3rd IF signal is obtained.

Mechanical Filter and IF Amplifier

    456kHz 3rd IF signal is filtered by a Collins Mechanical Filter, and fed to the IF amplifier consists of Q5 and Q6.
    Here you see the Collins mechanical filter mounted on the IF board by means of the 2 transistor sockets. The bilateral design permits the filter being used both in the Rx and Tx operation; signal flows bidirectionally. The filter module is secured by an L shaped metal piece (screw loosened in the picture).

Ring Modulator

    The 3rd IF signal is applied to the ring modulator, which has 4 diodes. Output from the 456kHz crystal carrier oscillator is also given to here, the demodulated audio signal is obtained.

Audio Amplifier

    The audio signal obtained by the ring modulator is amplified by the first audio amplifier, Q2. Output is taken from the collector of Q2, and again amplified by the audio driver transistor, Q1.
    Output of the driver is fed to the audio power amplifier Q20 which is mounted on the back panel. This is a class A amplifier having the output transformer. It drives the built-in front firing speaker. No headphone jack is provided.

Volume Control

    In the ordinary receiver the volume control is a passive attenuator device reducing the input level of the audio amplifier. It means that the HF circuit gain is unchanged even if the volume control is lowered. The SB-34's Volume Control is, on the other hand, truly a gain control governing the entire receiver. The volume control knob defines the gain of RF mixer, 456kHz amplifier, and slight amount of the 1st audio amplifier gain. Other stages work in full gain unless AGC voltage is present.
    The volume control is an ordinary potentiometer connected to the DC12V power supply line, and the gain control voltage is taken from the brush of the potentiometer. This control voltage changes the transistor base voltage of each stage controlled.


    SB-34's AGC is an audio-delivered type referencing to the speaker voltage. Voltage is taken from the speaker terminal and given to the AGC transistor, Q3. As the audio output becomes higher, Q3 conducts between collector and emitter. Collector voltage of Q3 is almost same as the power bus line, DC12V, if no audio presents. It goes lower as the audio output goes stronger.
    The AGC oltage generated in a manner described above is applied to the RF amplifier Q11and IF amplifier Q5/Q6, reducing the gain of those stages. The distribution of the AGC voltage is such that the RF amplifier would be cut off even for the average strength of the incoming signal. This arrangement keeps the following stages from being overloaded.
    When the incoming signal disappears, the AGC voltage slowly rises back to DC12V, returning the receiver to the full gain.
    When the volume control is turned more than 50%, a diode connected to the AGC transistor starts to clip the speaker voltage. As a result the input to the AGC transistor becomes lower, reducing the AGC voltage, thus the louder sound. At the maximum volume control setting, the AGC transistor input is completely clamped, therefore the all the stages works in full gain regardless of the signal strength.

Drawback of the design

    This unique Volume and AGC design brings the several obvious drawbacks to the 34.

Band Selector

    The Band Selector knob is the highlight of the mechanical genius of the SBE. It rotates approx. 330 degrees. It switches the operation band and adjusts the RF tank circuit.
    As the knob is rotated, a reduction gear drives the triple ganged tuning capacitor. The knob also switches the band selection rotary switch via a cam mechanism called Geneva Mechanism. The mechanism also changes the slug position of the 3 tuning coils.

    For example if you operate in the 20 meter band, the knob is set between 9 o'clock to 11 1/2 o'clock range. Within this range, the knob can be rotated lightly (only the gang tuning cap is driven), and it should be adjusted so that the maximum reception gain can be obtained.     And if you want to switch to 40 meter band, the knob must be set between 12 o'clock and 2 1/2 o'clock range. When the knob setting goes from a band range to the other, you need to give more torque to the knob. And in this moment the Geneva Mechanism rotates the band selection switch and moves the coil slug position. The shape of the knob is designed so that this operation can be made easily.

    This Geneva Mechanism provides easy operation with single knob. It also prevents the tuning caps from being adjusted to the harmonic position.

Transmitter Output Section

    Right behind the speaker the transmitter output section is located. This high voltage section is guarded by a metal grill (removed in the picture). Tubes are mounted horizontally. No active ventilation is provided. Horizontally mounted slim coil near the speaker yoke (seen above the yoke in the picture) is the TVI suppression coil.

Transistors Used in SB-34

SB-34 Desig. Usage Transistor Manufacturer Type Substitution Information
Q1 AF Driver 2N2431
PNP Alloy ACY33, AC128,AC138H, AC138, AC139K,AC139, AC142H,AC142H-K,AC142K,AC142, AC153K, AC153, NKT281 AL/1
Q2 AF AMP 2N3638(2N1305)
PNP Alloy BC126,BSX40, S1829, TQ63A, TQ63, 2N2927 A/1
Q3 AGC AMP 2N3642(2N2926) (GE) NPN Silicon

Q4 MIC AMP 2N3638(2N1305)
PNP Alloy

Q5 IF Amp, TX 2N2672 Amperex PADT

Q6 IF Amp, RX 2N2672 Amperex PADT

Q7 VFO Mixer, TX 2N2672 Amperex PADT

Q8 VFO Mixer, RX 2N2672 Amperex PADT

Q9 RF Mixer, TX 2N2672 Amperex PADT

Q10 RF Mixer, RX 2N2495 Amperex PADT SUBST: NTE160
TO72 T-PNP, Germanium for RF-IF Amplifier, FM MIxer/OSC
Vcbo 30V, Vces -20V, Vebo -0.3V, Ic 10mA, Pd 100mW, hFE 50 typ, fT 550MHz typ

Q11 RF AMP 2N2672 Amperex PADT

Q12 456kHz LOC OSC 2N2672 Amperex PADT

Q13 456kHz DBLR/TRPLR 2N2672 Amperex PADT

Q14 VFO Buffer 2N2672 Amperex PADT

Q15 VFO OSC 2N3564(2N706) (RCA) NPN Silicon

Q16 Keyer, RX Bus 2N3462(386-7185P1) (Raytheon) NPN Alloy

Q17 Keyer, TX Bus 2N3462(386-7185P1) (Raytheon) NPN Alloy

Q18 VFO Volt.Reg. 2N2926 GE NPN Silicon

Q19 HF OSC 2N2672 Amperex PADT

Q20 AF OUTPUT 2N2869/2N301
PNP Power

Q21 Power Inverter 2N443
PNP Power

Q22 Power Inverter 2N443
PNP Power

Q23 Ext.Linear Ctrl 2N2926 GE NPN Silicon

30 minutes of Limited Operation Time...?

    I acquired this SB-34 at the Livermore swapmeet, and it was the first day on my way traveling to Canada, a week long vacation I and my wife had been waiting for. When we arrived at a motel in Oregon, I could not help starting the test of the new radio. The AC power cable came with the rig, and I turned it on. The radio skipped the most exciting moment, 15 seconds filled with great anxiety. Yes, this is solid state... the radio immediately came back to life with warm color of the dial illumination.

    Since I did not have an HF antenna, I connected a power cable for my laptop computer to the antenna terminal using a paper clip. It worked as a short wire antenna. Receiver seemed to be working. The radio picked up several stations on 7MHz calling CQ contest.

    Returned to Silicon Valley I fired up the radio on my workbench with a random wire antenna and my antenna tuner. Although the audio volume seemed weak, the receiver picked up South America and Australia. Then, after a while, sensitivity suddenly dropped, and finally, even the background noise faded into silence. I was puzzled and tuned the dial. The receiver still worked at the lower frequency in the same band. I continued to monitor CW stations but eventually the receiver died completely. The radio was obviously in trouble.

    In the next evening I found the radio revived. Wondering what happened last night and I enjoyed monitoring DX stations. 30 minutes later, however, the sensitivity again suddenly dropped and finally it died again. Looks like the operation time is limited to 30 minutes. How can such thing happen?

Heat Caused the Trouble

    Tried many things, the symptom was as follows.
  • Reception is okay right after the startup.
  • When approx. 20 minutes passed, the sensitivity goes bad at the high end in the band. The loss of sensitivity is not only for the incoming signal but also the background noise disappears. The critical reception frequency of dead and alive moves toward the low edge in the band.
  • When approx. 30 minutes pass the receiver becomes dead for the entire band.
  • This happens in any band of the receiver simultaneously.
  • The radio revives after a certain time being powered off.
    This could be a trouble caused by heat. It was summer in California; the temperature of my garage lab was uncomfortably high even in the evening, although the garage door was left halfway open.

    Now it was the time to open the case. The metal sleeve case does not have ventilation holes except the vicinity of the final power amplifier. I guessed the overall ventilation should not be enough. I removed the case, and observed the internal configuration. No modification or fixing attempt was found.

    The receiver kept operation much longer if operated without the case, but eventually it lost its consciousness. The receiver revived temporary, if I use a Japanese "Uchiwa", or hand fan, to apply air flow to the receiver. It confirmed the heat as the primary cause of the trouble. I placed small electric blower fan (used for PC power supply). The receiver maintained its conscious after the several hours of operation.

Pointing out the problem

    I soon suspected the VFO ceased its oscillation. Somehow the VFO stopped operation when it got hot, therefore the intermediate frequency could not be generated. This hypothesis clearly explained the phenomenon observed. As a matter of fact, the sensitivity immediately came back if slight airflow was applied to the surface of the VFO board.

    The VFO circuit generates frequency between 5.4569MHz and 5.7069MHz, regardless of the band. The circuit consists of 2 transistors; one is the oscillator and the other is the buffer amplifier. I checked the VFO output in a way suggested by the service manual. Placed another shortwave receiver beside the rig, and connected a test lead wire to the VFO output. By winding the vinyl test wire to the whip antenna of the potable shortwave radio, it could then be used as a signal strength meter. The test proved my hypothesis - VFO output rapidly dropped when the circuit got hot, and eventually no signal was generated by the oscillator.

Added a resister

    In a weekend afternoon I kept the garage door closed. Californian summer afternoon sunlight turned my lab into a nice temperature chamber. Now the problem is easily reproducible and I measured voltages at the various points of the VFO circuit. What I found was that emitter voltage of the VFO oscillator transistor was very temperature sensitive. When this voltage exceeded the certain threshold, it caused the oscillator halt.

    In order to maintain the voltage within the operational range, I added a resistor to the bias circuit. It made the oscillator stable in operation even if constantly used under the high temperature. The problem was solved.
    However, the true reason is still unknown. I guess the property of the transistor or resistors was changed due to aging.

Weak reception

    Now the reception is satisfactory stable- also stable in weak volume. Although my antenna is mere long wire swinging in the backyard, MFJ preamplifier-tuner should provide enough RF signal to the receiver. The operating manual states that volume control at 50% position gives enough volume for the indoor use. In a reality the volume control must be full in order to archive the usable audio.

    Insufficient gain of the audio stage was suspected, however, the speaker blasted me when a local San Jose HF station began calling CQ. The audio output stage itself seems to be functioning normally.

    By injecting CD player output into the audio driver, it was confirmed that driver stage also functioning as expected. The sound is very dry, communication equipment taste. It's not a receiver for listening entertainment program in any way so this is not a problem.

Start Tweaking

    The first suspect was the AGC and volume control circuit which is in very unique design. If nothing is done, this radio will remain useless so I decided to start tweaking.

    The volume knob controls not only the audio gain but also the IF gain and RF mixer gain. AGC line controls RF mixer gain too. The RF amplifier and 1st frequency converter (RF mixer) is wired on a "RF board" located under the chassis. So I disconnected the AGC line and volume control line from the board, and replaced them with fixed voltage so that the RF board would always work with full gain.

    With this configuration, strong signal became heavily overloaded, seemed like the board was actually working with full gain. However the audio from speaker was still not loud.

Spark and Exposed Gem

    I mounted an extra rug terminal board to the RF board to provide an easy hookup for the multimeter. AGC line from IF board was then connected here. The time constant capacitor of the AGC circuit might loose its capacity, so I added the new capacitor on this rug terminal board and removed the original one.

    During the modification, ZAP!!!!! I saw a spark from the tip of the soldering iron, and something flew away and hit something at the corner of the garage shop. I soon realized that one of the transistors was exposing its gem - plastic mold was blown up. The receiver was completely dead when powered up.

    The power cable had been disconnected at the moment of the incident, but the chassis had been connected to my old oscilloscope. It seemed like my soldering iron leaked, electric current flowed from the iron to the scope, damaged a RF board. Oh my...

    Damaged component was a 2N2495, a transistor for the Rx RF mixer. Although the type is different, the receiver worked weakly, when I placed the Tx RF mixer transistor on the Rx RF mixer socket. I was in need of a 2N2495 or its compatible transistor.

    No exact part found at Halted Specialties. I purchased several similar PNP Germanium transistors, but none of them gave the life to the receiver as before. Transistor substitution manual suggested there is no direct substitution. Searching web found nothing.

    NTE would be the best destination in such a case as this. It sells many replacement semiconductors with NTE original number. The NTE replacement for 2N2495 was NTE160. Halted Specialties carried a stock so I purchased one. Cost $4.00, pricey but worth to pay. Although NTE160 was a replacement, its packaging was different and could not be inserted into the socket on board, so I had to solder it directly. The receiver came back to life.

    But pay attention from now. Better to disconnect all the wiring for the measurement, in addition to the power connection. Of course the best solution would be to buy a good soldering iron, though...
SB-34 Testing

Ultimate method of investigation

    Now, let's return to the troubleshooting, the weak volume. I measured voltages at various points and monitored waveforms, but no true find. Could it be in the RF stage or the IF, or may be a bad balanced mixer. Could it possible the Collins mechanical filter has something wrong, or is it the true performance of SBE?

    Spending several nights, the mystery was still unsolved. No more idea came up in my mind. My exhausted biochemical computer then discovered an ultimate and brilliant solution... Compare to another working rig! But, hey, there's nobody having SB-34 nearby.... I surfed the web seeking the answer and what I found was... a working SB-34 for sale! Without getting my wife's approval, my finger clicked a button of the mouse.

    Two weeks later, two SB-34 sit side by side on the workbench of my lab.

Modification of the SB-34 #2

    The SB-34 #2, which cost me more than #1, had a genuine SBE hand mike and service manual, and was cosmetically original. It played beautifully with plenty of volume.

    By opening the cover, modification was immediately apparent. Most obvious thing was the crystal calibrator board which seemed to be a general purpose kit, not a SBE genuine product. The genuine option calibrator unit was designed to be mounted on the back panel of the SB-34. This unidentified board had an identical connection to the genuine option, so shouldn't be a problem.

    All of the electrolytic capacitors in the receiver circuit had been replaced. Desoldering and resoldering work was observed throughout. Especially at the AGC circuit, virtually every point was reworked. The previous owner should have already paid efforts I was considering. And most important thing is that this unit is working perfectly. No more better example could be expected.

    I had discovered many differences of component values used, between circuit diagram and the #1 radio. The manual which came along with #2 radio was newer than the first one. The component values of #1 radio matched with #2 manual; i.e. #1 and #2 radio are the same revision, and the #1 manual was older.

Side by Side

    Side by Side, was indeed a powerful method. The answer was lying in front of me. All I had to do was to check and compare, and all I need was the effort and patience.

    As a brute force method, I tried to swap the circuit board. Not a physically swapping, but disconnect the wiring between the boards and interconnect the #1 and #2 radio. As a result, the problem was tracked down to the IF board. When I connected the #2 VFO board output to the #1 IF board, reception was weak. On the other hand, #1 VFO and #2 IF board worked well.

    Swapping the mechanical filters did not show any difference, therefore they were okay. This was a good news; if the mechanical filter was broken, the cost of the replacement would be, if ever obtained, more than a half of the original purchase price of the radio. As far as the price was concerned, a SB-34 could be a mechanical filter with all surrounding circuit attached.

    Comparing the ring modulator, which employed four diodes, did not show a big difference. Audio drivers and power amplifiers seemed to be working identically.

    From these observations, I became pretty sure that the 1st audio amplifier right after the ring modulator had the trouble.

Just a 1 Transistor Amplifier

    The 1st audio amplifier, is just a single transistor. Almost there! Nothing should be tough anymore. Nevertheless, I could not determine the true cause. Although it was basically a simple amplifier, the circuit was connected to the microphone amplifier and keying control which switched Rx and Tx. I disconnected those circuit in order to separate the problem, couldn't find the cause. Tried another transistor, replacing capacitors, and even built a new amplifier circuit and replaced with it.... still no luck.

    Honestly speaking I haven't gotten a formal education of analog electronics in a school or an university. Strongly realized the necessity of basic knowledge, started to read electronics textbooks including ARRL handbook, refereed my dictionary for unfamiliar English words, back to the radio and tried something different, again returned to the textbooks....

    Tired with a deep frustration of not being able to fix a mere single transistor amplifier, I picked up some capacitors removed from the radio. My analog circuit tester reacted when quality-looking black plastic mold electrolytic capacitors were connected, as if the capacitors were laughing at me.

    However, I noticed that one of those black small caps did not catch the instrument's attention. The marking read 10uF, the tester should respond for its charging current. What was this capacitor all about? Quickly checked the radio, and I found that I had removed from the radio but not replaced with a new one. Placed a new old stock capacitor, the amplifier started to amplify!

    It was an audio frequency bypass in the emitter circuit. Two capacitors were connected in parallel, another one was a 0.1uF. If this 10uF was missed, audio bypass was far less than ideal, thus the low gain of the amplifier. What a simple cause! Ashamed with my poor troubleshooting skill, but I felt quite happy with very loud voice someone shouting the "CQ contest!".

Future Improvements

    Restored the tentative test wiring to the original, readjusted the RF oscillator. The fixing was completed, at least for the obvious receiver problem. The #1 is much much powerful than before, but a little weaker than the #2. Replaced RF mixer transistor might be the reason, while the entire re-alignment would be necessary.

   AGC circuit should be the next task. Frequently adjusting the volume control was necessary, which was annoying especially monitoring the net operation. The #2 showed almost the same behavior, so I guess this was the original characteristic of the SB-34. So, in order to improve, the AGC circuit arrangement should be modified. But how could it be made? Perhaps its unique volume control concept will be abandoned and regular AGC method will be used. If such modification can be done, adding a S meter functionality would also be possible.

    Since I did not have a proper antenna capable for transmission, Tx part was untested for both units. I pressed the PTT button for less than a second and I could hear a squeak from other unit to which the antenna was not connected. Therefore it looked transmitting somehow, but not knowing how much power it could produce. Some SB-34 owners (or restorers) reported on the Internet that they suffered weak transmitter, seems it is a common problem to the 34. Reportedly the frequency stability is not sufficient while transmitting, due to the marginal ventilation. These points must be carefully checked someday. Although not active right now, SB-34 back-on-the-air project is still in progress; I purchased a new dummy load and a SWR/power meter solely for this project!
SB-34 at San Jose Lab

Go to SB-34 Prototype page

Return to Restoration Projects
Return to NoobowSystems Lab. Home

Copyright(C) NoobowSystems Lab. San Jose, California 1998
Copyright(C) NoobowSystems Lab. Tomioka, Japan 2001, 2005

Sep. 16, 1998 Created.
Nov. 22, 1998 Divided into multiple pages.
Jun. 16, 2001 English version, reformatted.
Sep. 10, 2001 Reformatted.
Sep. 14, 2001 Retouched.