Henry HF RF AMPLIFIER Henry RF Amplifier Information Center


Information Center

 Page Updated on:  01/03/2014

2K Classic (left) / Pair 2K-4 (center) / 3K-A (right)


*** DANGER ***

RF Amplifiers Have Lethal HIGH VOLTAGE Inside


About This Web Site:

The information contained on this web site is a FREE knowledge exchange for older Henry vacuum tube RF amplifiers. All information listed is an accumulation of lessons learned by multiple different  individuals when modificating or repairing their Henry RF amplifiers. There is no guarantee the information is error free, so utilize it as reference only. Perform all modifications and repairs to your equipment at your own risk. If you have additional information on Henry RF amplifiers which you would like to share with others, email mayo(at)ne7x(dot)com and I will add your information to this web site.






Henry 1KD-5

3KD Premier 1-of-2

3KD Premier 2-of-2

Henry 2KD-3

Henry 2K

Henry 2K Ultra

Henry 2K-4

Henry 2KD/3KD

Henry 2K-2

Henry 2KD-5

Henry 2K Classic

Henry 2K Classic X

Henry 2K-3 Henry 2K-3 (Schematic)   SS750_SS1200

Henry 3K-A

Henry 3K/8K Ultra

Henry 3K Classic

Henry_3KD_Premier (8877)

Henry 4K-2

Henry 4K Ultra

Henry 2002/4/6 VHF

Henry 5K


CAUTION when using or referencing original factory Henry Radio schematics.

The schematics are known to have wiring errors.

Double check wiring against other designs and do not assume the Henry Radio schematic is 100% correct.

EXAMPLE: The 2K-Classis schematic shows BIAS zener 'D1' in backwards.



Henry Radio RF Amplifier Model Numbers and Specifications


Past ARRL QST Magazine Product Review Articles

Henry Radio; 2-K Linear Amplifier; Jun 1965

Henry Radio; 2K Ultra Amplifier; Jun 1972

Henry Radio; 2K-2 Linear Amplifier; Nov 1967

Henry Radio; 2K-4 Amplifier; May 1974


Henry Radio Magazine News Article, October 1981

Supplied by: AB8VJ



Henry 2K Ultra


Henry 4K Ultra


Henry 8K Ultra


2K-4 RF Output Video 4K Ultra RF Output Video 4K Ultra Inside Chassis Video
3K Ultra RF Output Video 2K Ultra RF Output Video 3CX10000A7 Video




Amplifier RF Output Tuning Procedure

By: NE7X


Tuned Input Adjustment

SWR Match Between Transceiver Output & Amplifier RF Input

By: NE7X


Internal RF Deck Chassis Removal

Pedestal Cabinets

By: NE7X



Modifications / Upgrades:

Henry 2K Classic

Metering Circuit and HV Protection Upgrades

By: NE7X

Tear-Drop Meters

Information about Tear-Drop meter replacement

 By: NE7X


Henry 5K Classic

Blower Fan / Step-Start

by: K7EM



2K-4 / 3KA / 2K Classis

By: NE7X


Step Start Modification



When Good Enough Just Isn't



Henry 2K-Classic 10 Meter Modification



Henry 3KA Conversion to 5K



Henry 2K Classic X Conversion to 5K



The Henry 2K Project

By: Fred KC5RT (For: WS0B)


QSK Modifications:

Henry 5K Classic

By: K7EM


Original Henry 2K

By: NE7X


Henry 2KD-5

By: NE7X

Henry 2K-4 and 3K-A

By: NE7X

SEQ-QSK Sequencer & Vacuum Relay Issues/Fixes

By: NE7X


Troubleshooting / Repairs:

Troubleshooting Tips

By: Henry Radio


Blower Fan Replacement - Henry 2K-4



Blower Fan Replacement - Henry 5K

By: K7EM

HV Drops to Zero when Amplifier is Keyed

By: NE7X


HV Arching / Popping

By: NE7X


Intermittent High SWR



BIAS Zener Failure

By: NE7X


Low RF output, No Ip Dip



ALC Zener Failure

By: NE7X


300ma Plate Current When HV is Applied, No Drive

By: K2MF


AC Breaker/Fuses Blow When Powered ON

By: AA7A


Ip & RF Output Slowly Increases After Amplifier is Keyed

By: NE7X


RF Amplifier Parts:

Radio Dan - W7RF Henry Radio RF Parts Company
eBAY Henry Radio   Ameritron 3-500G RF Tubes
Gigavac Vacuum Relays SEQ-QSK Sequencer Harbach Electronics
Ohmite Power Resistors Electrolytic Capacitors BIAS Zener D1
Hyper Plate Caps for 3-500Z 3-500G RF Sockets QRO Parts
RF Band Switches eBAY RF Band Switches Refurbished Front Panels

The Medallion shape of the MM-series by Jewell Instruments is a close design substitute 
for the original Tear Drop design by Parker from the 1960s.

 For Henry amplifier restorers, this is an option when desiring to retain design aspects of these original Henry classics.


Non-Henry RF Amplifier Information:

External QSK-2KW Interface

External QSK interface that can be connected to any vacuum tube RF amplifier

By: NE7X


Ameritron AL1200 QSK Modification

By: W2NO


RF Amplifier Technical Web Site

By: W8JI


T/R Relay Escalator

Inexpensive way to increase the switching time for slower mechanical T/R relays

By: K6KK


Adding 160 Meters

By: AG6K


Heathkit SB-200 Modifications



RF Vacuum Tubes:



By: NE7X


Tube Specifications

By: RF Parts


Triode Data Sheets



Web Page Editorial:

Henry RF amplifiers maybe big (34" tall), heavy (150+ #s) and old (1960-1990s), however high power RF amplifier technology has not changed much over the years. Transistor RF amplifiers are becoming smaller and more reliable, however most are not built to commercial continuous duty-cycle specifications like Henry RF amplifiers are.  Plus newer solid-state RF amplifiers can be 4X the cost over an older gently used Henry RF amplifier.

Henry RF amplifiers are very easy to work on with lots of room to get your hands and tools inside, and parts are still available and affordable. A well maintained Henry RF amplifier will still be around putting RF output and breaking DX pile-ups long after I become a SK.

Some hams may say "dip-n-loading the plate Ip is a pain," however I find this a feature. Having a pi-output network allows me to bring the RF amplifier to maximum RF output resonance when the antenna is a few Z-ohms off.  Unlike a transistor solid-state RF output circuit, an adjustable pi-output circuit allows for maximum transfer of RF power while tolerating a higher SWR.

There is also the "Fun Factor" in owning and operating a Henry RF Amplifier. The thrill of receiving a signal report and comments from the stations you are in QSO with,  "You are the loudest signal on the band!" Or the impressive looks and comments you receive by visitors to your shack when they see the heavy metal Henry RF Amplifier sitting next to your operating desk. Just look the the picture at the top of this webpage. Having that "BIG GUN" shack appearance is worth another 10dB !

Personally I prefer Henry RF Amplifiers with 3-500Z type tubes. The 3-500Z tube in my opinion is: very durable, will tolerate abuse (miss-tuning), relatively available and easy to obtain, instance-on, a pair provides full-legal-limit RF output and best of all, has the best "Power-To-Dollar" value ratio. Having multiple Henry RF amplifiers all using the same type of RF tube allows me to only need to stock one type of tube for inventory spares.

I have received emails asking me to repair a Henry amplifier if its shipped or delivered to me. At this time I have to decline. I am still working full time for a living and have many personal commitments consuming my time. However if you have a particular issue or question, I will gladly respond to all emails and provide some suggestions what you can try doing to resolve the issue yourself. Once you have the issue resolved, I would appreciate a return email informing me what the final solution was.

So whatever your manufacturing choice is in RF amplifiers, tubes or transistors, life is too short for QRP! Enjoy the hobby & happy DXing.

73s Thomas NE7X