Kenwood TL-922

Two Eimac 3-500Z bottles, a 2 kW PEP rating, and a reputation for being one of the most compact ways to put legal-limit power on the air.

Overview

The TL-922 is an HF linear amplifier built around a pair of Eimac 3-500Z transmitting triodes. These are the same zero-bias, Hi-mu glass bottles that show up in every serious grounded-grid design of the era. Kenwood's spec sheet for the TL-922A lists it as a Class AB2 grounded grid linear amplifier, and the circuit description says why. The grounded grid arrangement needs no neutralization. The low input impedance means no cathode-swamping resistors are required. The excitation energy is added to the RF output rather than lost, so the amp uses every watt of drive from the exciter.

The headline numbers are 2000W PEP SSB and 1000W DC CW/RTTY input, per Universal Radio, RadioWorld, and weca.site. Three sources agree. The arimi.it documentation quotes 1000-1300 watts of output across 9 bands. That is output rather than input, so the two figures describe the same amplifier from opposite ends of the signal chain. An owner on eHam, having owned the amp for over a year, reports it "puts out 1300 watts easy, super cool running". The 3-500Z pair was rated for far more abuse than most hams ever throw at it.

What makes the TL-922 interesting isn't just the power. It's the packaging. The arimi.it documentation calls it "one of the best, sturdiest and compact pieces of equipment for radio amateurs," and Kessler Engineering — who sell a revival kit for the thing — describe it as "a relatively low-cost HF linear amplifier with outstanding ergonomics." Compact, sturdy, ergonomic, cheap. Those four words don't usually cluster around a legal-limit amp, and they're a big part of why the 922 has stayed in rotation decades after it was discontinued.

A note on naming: sources use "Kenwood TL-922," "TL-922A," "TL922," and "Kenwood TL922A" more or less interchangeably. Kessler Engineering treats them as a single family ("The Kenwood TL-922/TL-922A"), and the arimi.it modifications page uses the header "KENWOOD TL-922 (TL-922A, TL922) MODIFICATIONS." If you're shopping, assume the A suffix denotes a revision rather than a different amplifier.

Key Features

Two Eimac 3-500Z Triodes in Grounded Grid

Four separate sources - arimi.it, Universal Radio, RadioWorld, and weca.site - confirm the tube complement: two 3-500Z high-performance transmitting tubes. These aren't obscure bottles. They're the standard high-mu zero-bias triode of the era. The manual's circuit description notes that the tubes are heated by a center-tapped filament transformer requiring only half the usual current, which prevents voltage drop due to wire resistance. Some later listings show 3-500Z graphite variants (3-500ZG) from RF Parts going into restored units, but the original spec is plain 3-500Z.

2000W PEP SSB / 1000W CW Input

The rated plate input is 2000W PEP on SSB and 1000W DC on CW and RTTY. Universal Radio, RadioWorld, and weca.site all state this identically, and the ResearchGate PDF frames it as "up to 2kW PEP on SSB and 1kW on CW on 9 bands." The manual's own duty-cycle ratings are worth knowing before you buy one: SSB continuous for 30 minutes, CW and RTTY key-down continuous for 10 minutes. The amp will do it, but the tubes and transformer are being asked to work, and the thermal protector is there for a reason.

Two Front-Panel Meters

Universal Radio, RadioWorld, and weca.site all note "two meters for maximum operating convenience." On a legal-limit amp you need to watch plate current and RF output simultaneously while tuning. Having both meters on the front panel means you're not flipping a switch mid-load. Kessler Engineering is probably thinking of this when they praise the 922's "outstanding ergonomics."

80 Watts of Drive Is Enough

Universal Radio states drive power is "80 or more watts." The manual is more specific: an exciter with 50Ω output impedance and 80W to 120W RF output is sufficient, and anything exceeding 120W will cause overdrive, with shortened tube life and distorted output. If your exciter can't be throttled, you'll want one with an external ALC input terminal. The manual lists a long roster of Trio-Kenwood exciters that were designed to match the 922 in both function and appearance, including the TS-930, TS-830, TS-820, TS-530, TS-520, TS-430, TS-180, TS-130, TS-120, and TS-900 transceivers, plus the TX/T-599 transmitters.

Bias and Idle Current

Kenwood recommends an idle current of 200 mA in SSB and 100 mA in CW. That matters when you're setting up the amp or troubleshooting a mod. egloff.eu documents a bias modification using seven 1N5408 diodes, noting that adding a diode reduces the current inversely. If you're buying a used 922 that's been through a "facelift," ask what was done to the bias circuit.

Not for QSK

Universal Radio's listing includes the parenthetical "(Not for QSK)". Full break-in CW operation isn't in the cards. For contesters running QSK this is a real limitation. The amp handles CW and RTTY fine, just not the fast T/R switching that QSK demands.

240V, 14A Operation

Listings show units set to 240V AC drawing 14A, which matches the kind of power a legal-limit amp needs. The manual's power cable section notes that the supplied cable has no plug at the end. The blue and brown leads are power, the green lead is ground. If you're buying one sight unseen, confirm the voltage configuration matches your shack before you plug it in.

Historical Context

The ResearchGate PDF describing the TL-922 notes the first TL-922 power amplifiers are "now well over 40 years old." Universal Radio lists the model as "Discontinued!" The design intent, per Universal Radio and RadioWorld, was to "provide the maximum legal power." Kessler Engineering calls it "relatively low-cost." It was never a halo product, just a working amplifier at a working price.

The service documentation that survives is unusually thorough. A service manual package for the TL-922 consists of the TL-922 Service Manual, the TL-922 Instruction Manual, a "Circuit Improvements for the TL-922" printout, a "TL-922 10 Metre Hints" printout, and a "Kenwood TL-922/A Modifications" printout. That's a lot of paperwork for a single amp. The 10-metre hints document in particular suggests the amp's band coverage was a subject of ongoing interest - see below.

Collectibility & Value

The 922 has a known-issues list that any buyer should read before handing over money. W8JI documents three specific problems: "The TL922 had the wrong type of capacitors at CL," "Kenwood TL922A Unsuitable loading capacitors. This type of capacitor is unsuited for high RF currents, and is unstable with temperature changes," and "bad socket wiring grid system problems." Those are the kind of faults that show up as instability, arcing, or intermittent output.

The aftermarket has stepped in. Kessler Engineering sells a "Kenwood TL-922 Revival Kit" at $385.00. Jahnke Electronics has listed restored examples with "all update mods completed," specifying nichrome parasitic suppressors, brand new 3-500Z graphite tubes from RF Parts, and an FB-922 filter cap replacement kit from Harbach Electronics. Egloff.eu's "TL922 facelift" article documents the bias mod. The parts are largely still available.

Spare parts turn up with some regularity: power/mode rocker switches (S36-2401-05), original doorknob capacitors (RDC-40, 200 PF ±5%, TVDC 4 KV), original ceramic tube bases sold in used pairs, and tube socket/fan/chimney conversion kits to adapt 3-500Z mounting holes. Market listings have appeared on eBay, hamamateuradio, Jahnke Electronics, and HifiShark, though no source gives a verified current price for a working unit. The only firm number in the research is the $385 revival kit. Treat any asking price you see as a starting point for negotiation, and budget for the mods if they haven't already been done.