Note
The SB-310 was released for Christmas in 1967 and is an SWL version of the SB-301. It took very little re-engineering to convert the SB-301 to an SWL unit, enabling Heath to tap into a new market for almost nothing.
The SB-310 uses 11 tubes (including the LMO) and is virtually indistinguishable from the SB-301. What visually differentiates these two receivers are the name plates, the markings on the band switches, and the rear panel connections. For a discussion of the 310’s specifications and design, refer to the SB-300 and SB-301.
The SB-310 is not a general coverage receiver. It is designed to cover the 16, 19, 25, 31, 41, and 49 meter international broadcast bands; the 80, 40, and 20 meter ham bands; and the 11 meter Citizens Band. Specific frequency coverage is as follows: 3.5 to 4.0; 5.7 to 6.2; 7.0 to 7.5; 9.5 to 10.0; 11.5 to 12.0; 14.0 to 14.5; 15 to 15.5; 17.5 to 18.0; and 26.9 to 27.4 MHz. Note that some of these bands have since been reallocated.
An optional kit (SBA-310-3, 1974) converted the 11 meter Citizens Band to 13 and 15 meter shortwave coverage (21.3 to 21.8 MHz). The conversion is easy to spot since it included a new dial legend plate on the band switch.
The SB-310 will tune USB, LSB, AM, and CW but came out of the box with only a 5 kHz AM filter. Note, this is the wider filter, as opposed to the narrower 3.75 kHz AM filter that was used with the SB-301, for example. Refer to SB-100 for a discussion of available crystal filters. A CW and two different SSB filters were optional. The SB-310 will not function in CW or SSB unless the appropriate filters are installed. The filters are the same ones used in the SB-301, but not the same as in the SB-300. The filters are small rectangular modules located between the LMO and the S-meter and are (from front to back) CW, SSB, and AM.
The front panel controls are nearly identical to the SB-301, the exception being the absence of the concentric VHF converter selector on the RF gain control.
Rear panel connections include RCA jacks for 50Ω antenna input, mute (duplicates the function of the front panel STBY/OPR switch), 500Ω audio output, 8Ω speaker, hi-fi output, and a spare. The hi-fi output provides a line-level signal for connection to a high fidelity amplifier or receiver, for example.
In 1973 the SB-310 was replaced by the solid state SB-313. The SB-310 enjoyed moderate success but never achieved the popularity of Heath’s low-cost, general coverage “GR” and “SW” series receivers. It’s a pity Heath never made a full general coverage SB series receiver—it would have been a best seller. SB-310s have always been scarce and because of their similarity to the SB-300 and 301, they are easily overlooked at swaps.
References:
Review. Popular Electronics, Apr 1968, p. 72.
Brief description. Popular Electronics, Oct 1968, p. 54.
Increase friction in worn zero set. QST. Jan 1973, p. 52.
Zero-set dial modification. QST. Feb 1980, p. 44.
Frequency coverage (MHz): 3.5 to 4.0; 5.7 to 6.2; 7.0 to 7.5; 9.5 to 10.0; 11.5 to 12.0; 14.0 to 14.5; 15 to 15.5; 17.5 to 18.0; and 26.9 to 27.4 (21.3 to 21.8 MHz option replaces 26.9 to 27.4 MHz)
IF: 3395 kHz
Stability: < 100 Hz per hour after 20 minutes warmup; < 100 Hz for ±10% line voltage variation.
Visual dial accuracy: within 200 Hz on all bands
Electrical dial accuracy: within 400 Hz on all bands after calibration to nearest 100 kHz point
Backlash: < 50 Hz
Sensitivity: < 0.3 µV for 10 db signal plus noise-to-noise ratio for SSB
Overall gain: < 1.75 µV for 0.5 watts audio output
Modes: LSB, USB, CW, AM
Selectivity:
AM (supplied filter): 5.0 kHz at 6 db down, 15 kHz maximum at 60 db down
SSB (deluxe optional filter): 2.1 kHz at 6 db down, 5.0 kHz maximum at 60 db down
SSB (standard optional filter): 2.4 kHz at 6 db down, 7.0 kHz maximum at 60 db down
CW (accessory filter): 400 Hz at 6 db down, 2.0 kHz maximum at 60 db down (optional)
Image rejection: 60 db or better
IF rejection: 40 db or better
Spurious response: all below equivalent antenna input of 1 µV except at 10.0, 15.375 and 27.1 MHz
Audio response:
AM: 200–4750 Hz nominal at 6 db (with supplied filter)
SSB: 350–2450 Hz nominal at 6 db (with optional filters)
CW: 800–1200 Hz nominal at 6 db (with optional filter)
Audio output:
speaker: 8Ω
hi-fi: 1000Ω
headphones: high impedance
Audio output power:
speaker: 0.80 watts with less than 8% distortion
hi-fi: not more than 10 µV signal is required for 250 mV rms output at 400 Hz,
30% amplitude modulated. Less than 10% distortion at 250 mV output.
Antenna input impedance: 50Ω nominal
Muting: open external ground at mute socket
Crystal calibrator: 100 kHz
Power requirements: 120/240 VAC, 50/60 Hz, 50 watts
Size: 15˝ wide x 6.75˝ high x 14˝ deep; Weight: 17 lbs
Tubes: (1) 6CB6, (1) 6BZ6, (3) 6AU6, (1) 6AB4, (2) 6BA6, (1) 6HF8, (1) 6AV11
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
