Henry HF RF AMPLIFIER 3-500G Tubes

3-500G Tubes

 Page Updated on:  01/24/2012


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RF Amplifiers Have Lethal HIGH VOLTAGE Inside



3-500Z RF Tubes:

3-500Z - Non-Graphite Data Sheet

3-500ZG - Graphite Data Sheet



The Original grounded grid triode introduced in the early 1960s. Anode power dissipation of 400 watts.   No longer in manufacturing production.


3-400Z replacement, having larger fins for increased anode power dissipation of 500 watts. Slightly larger body requires minor changes to fit where 3-400Zs were used. Requires heat dissipating connector.


Graphite anode version of 3-500Z. Anode dissipation of 600 watts (additional air flow may be required). Graphite anode provides a more rugged tube.


3-500G Filament Voltage


Symptom Of Weak Tubes


3-500Z (left)                                                                        3-500ZG (right)




Inside RF deck of Henry 2K-4

Don't you just love the warm Reddest Orange glow of those 3-500Z tubes !!!
You don't get this with transistors

Are the pair of 3-500G tubes in my amplifier good?

A quick, simple and easy test, key the amplifier for a few minutes in RTTY or continuous CW mode with 100 watts drive. Make sure you have an Ip dip and loading is optimum. A good pair of matched 3-500Z tubes with HV around 3600-3800 plate volts and 220-240 Ma grid current, you should get about 1200-1400 RF output into a dummy load/antenna. Both tubes should be equal in redness brightness and the percentage of redness on both tube's plate surface should be equal to each other. If none of the above is true, the tubes are weak and/or not balanced. I would consider replacing them with a new match pair.

Vacuum tubes are like light bulbs. If the filament is not burned out and there is no internal shorted elements, the tube will still have RF output, just a little less. You can save some money and just continue using it until it dies totally. The only concern would be, when it does finally fail, it could internally short causing a high voltage surge, resulting in damage to other components in the amplifier. To protect your amplifier from short duration high voltage surges caused by a shorting tube, you might consider adding HV pulse resistors to the HV circuit in your amplifier.



Life is too short for QRP!!

Happy DXing



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