Kenwood TS-820S (1976–197x)

Thirty-seven pounds of hybrid iron with a factory digital readout - the "S" that finally told you where you were on the dial.

Overview

The TS-820S is the version of Kenwood's hybrid HF transceiver that shipped with a digital frequency readout already mounted. The base TS-820 made you read a mono-scale analog dial and keep track of where you were. The S variant put the frequency in glowing digits in front of you. According to the manual, the digital dial indicates transmit and receive frequencies using carrier, VFO, and local oscillator signals rather than converting VFO frequencies, so accurate frequencies can be read at all times on any band and in any operating mode. The manual also says that since frequency accuracy is set only by the 1 MHz standard oscillator, you can read frequencies accurately up to 100 Hz order by calibrating against WWV. The green indication was chosen, in Kenwood's words, to assure many hours of fatigueless operation.

Under the hood, this is a tube hybrid - one 12BY7A driver and two S2001A or 6146B finals, with solid-state circuitry handling the rest. The receiver is a single conversion superheterodyne with an 8.83 MHz IF. Sensitivity is rated at 0.25 uV for 10 dB signal-plus-noise-to-noise. Image rejection is 60 dB. AF output is 1.5 W at 10% distortion into 8 ohms, and the external speaker connector accepts 4-16 ohm loads. The transceiver weighs 16.97 kg (37.4 lb) and measures 335×155×335 mm. It is a big desktop box, and it looks it.

Frequency coverage spans 10-160 meters across ten bands: 1.8-2.0, 3.5-4.0, 7.0-7.3, 14.0-14.35, 21.0-21.45, 28.0-28.5, 28.5-29.0, 29.0-29.5, and 29.5-29.7 MHz, plus WWV at 15 MHz for receive only. Tuning is analog and continuous. There is no repeater shift. Four optional crystal-controlled channels are available. Modes are SSB, CW, and FSK. There is no FM. Power comes from mains at 120 or 220 VAC, or optionally from 13.8 VDC via the DS-1A DC-DC converter. Current draw is 57 W in receive with heaters on, and up to 292 W in transmit at mains.

RF output is approximately 100 W PEP on SSB (200 W input), approximately 100 W DC on CW (160 W input), and approximately 60 W on FSK (100 W input). Spurious emissions are rated better than -60 dB. The microphone input is 50 Kohm through a 4-pin metal locking ring connector. The microphone input level is not stated in available documentation.

Key Features

Factory-Installed Digital Frequency Readout

The digital display is what sets the S variant apart. The TS-820S has it built in from the factory, and the base TS-820 does not. Sources describe the two as otherwise identical. The display reads transmit and receive frequencies to 0.1 kHz order. It uses the carrier, VFO, and local oscillator signals rather than converting the VFO frequency, so the reading stays accurate across bands and modes without recalibration per band. Calibrate the 1 MHz standard oscillator against WWV and the readout holds to 100 Hz.

Tube Hybrid Final Section

One 12BY7A driver tube feeds two S2001A or 6146B final tubes. This is the classic Kenwood hybrid formula - solid-state low-level stages, with vacuum tubes doing the heavy lifting in the PA. The manual describes the RF negative feedback and neutralizing circuit in detail. Negative feedback is applied to the tuning-type amplifier circuit including interstage LC tuned circuits, with approximately 6 dB of feedback via C5 and C10, yielding approximately 10 dB improvement in tertiary cross modulation products. The neutralization uses variable capacitors with rotors and stators floated from ground, which the manual claims achieves the same effect as the μ tuning type. Kenwood designed the circuit so that undesired oscillation won't occur even when gain increases to three times the optimum condition.

RF Speech Processor

During DX work, the speech processor increases talk power by converting the audio signal to a 455 kHz SSB signal and compressing it with a small time constant. The manual says this minimizes distortion and prevents tone quality deterioration compared to conventional clipper systems. Compression level is set with the COMP LEVEL knob while watching the meter. The processor level is set by changing the emitter bias of Q23 via the RF PRO variable resistor.

Built-In Monitoring Circuit

The TS-820S has a monitoring circuit that lets the operator hear their own voice during transmission. The manual points out that conventional transceivers of the period don't have this. The circuit can be used to check modulated conditions or to adjust the RF speech processor. It is energized only in SSB transmission, and diode switching prevents carrier leakage into the IF circuit.

Receiver Selectivity and Filtering

SSB selectivity is 2.4 kHz at -6 dB and 4.4 kHz at -60 dB. For CW, the optional YG-88C 500 Hz narrow filter brings selectivity to 500 Hz at -6 dB and 1.8 kHz at -60 dB. The optional filter operates at the 8.83 MHz IF. Without it, CW operators are working with the standard SSB filter shape.

Frequency Stability

Kenwood rates stability at within ±1 kHz during the first hour after power-on, and within 100 Hz during any 30-minute period thereafter. That first-hour drift is typical of the era. The rig needs to warm up before it settles, and after that it holds well.

Available Accessories

Kenwood offered a full set of accessories: the DS-1A DC-DC converter for 13.8 VDC operation, the SP-820 matching speaker with filters and two line inputs, the TV-502S 144 MHz transverter, the VFO-820 external VFO, and the YG-88C 500 Hz CW narrow filter. Transverter connectors are built into the rear panel. The VFO-820 gets its power from the TS-820 itself - 12.6 VAC at 40 mA, 12.6 VDC at 40 mA, and 9.0 VDC at 25 mA.

Historical Context

The TS-820S was manufactured in Japan starting in 1976. The end of production is listed as "197x" in available sources, with no specific year confirmed. One source describes production as running "from the late 1970s up into the 1980s," which does not fully line up with the 1976 start date. The product is no longer in production.

Some Kenwood radios of this era were produced under the Trio Electronics name before Kenwood's name change in 1986. Service bulletins for the TS-820S were issued under the Trio-Kenwood Communication name. The TS-820S belongs to Kenwood's "TS" series of HF transceivers, which cover the high-frequency bands from 1.8 to 50 MHz. Other models in that series include the TS-590S, TS-850S, and TS-430S.

Service bulletins for the TS-820 and TS-820S addressed the CW filter select control, speech processor alignment, a TA7201P substitution parts kit, a new display tube for the DG-1, a microphone input attenuator, and installing an AUX band. These were factory-issued documents, so Kenwood kept supporting the model with technical updates.

Collectibility & Value

The TS-820S sits in the middle of the hybrid Kenwood lineup. It is not the most sought-after model in the 520/530/820/830 family - that tends to go to later iterations - but it is the one that brought digital readout to the 820 platform. A source lists an MSRP of 5000.00, though the currency and year are not specified, so that figure is hard to interpret. Current market values are not well documented in available research.

Condition varies widely. Listings describe units ranging from "like new condition" with original box, manual, and service manual to working but cosmetically tired examples. One owner reported a mint TS-820S with the SP-820 speaker, AT2-220 antenna tuner, VFO-820 external VFO, and MC-50 microphone - a complete period station. Another listing noted the radio "works very good" despite being used. At least one unit was sold for parts.

Common problems cluster around a few areas. Display failures come up often - the DG-1 digital VFD display is a known weak point, and restoration procedures circulate among owners. A blowing fuse on power-up typically points to the rectifier unit board, which uses a voltage doubler circuit with four diodes (D1-D4). A shorted diode is the usual culprit. Mechanical issues include the drive sprocket and bandswitch coupling, both of which have documented repair procedures. At least one owner reported a unit with no output on 15 meters (21 MHz) for unknown reasons. Alignment procedures for the mono-scale dial and general calibration are documented.

Parts availability is a mixed bag. Some items are described as "great, hard to find" - the VFO plug, for instance. Accessory cables like the 9-pin VFO-820 cable appear on the secondary market. The TA7201P substitution kit was a factory response to a parts issue, which suggests that even during the production era, certain components needed workarounds.

Owner reception is generally positive on audio quality. One reviewer simply wrote "Great Kenwood audio." Another described the radio as performing "way above" expectations for its age. A more critical voice noted it is "missing the advancements of the past 50 years" - fair comment for a rig designed in the mid-1970s.