Henry HF RF AMPLIFIER Henry RF Amplifier B- Resistor


B- HV Resistor Failure

 NE7X - 10/26/2011



*** DANGER ***

RF Amplifiers Have Lethal HIGH VOLTAGE Inside



The 25 ohm 25 watt resistor in HV power supply B- line is a very common failure with Henry RF Amplifiers. This resistor connects from the negative HV rail to chassis ground. It is used for HV current imitating in case of a HV over-surge (kind of like a fuse). When it opens the HV plate voltage will drop to zero when the amplifier is keyed.


To test the resistor, remove all AC power from the amplifier, then remove the covers to expose the HV power supply. You must remove the wires from one end of the resistor, taking it out-of-circuit, then you can use a simple OHM meter to check the resistance. A good resistor should read ~25 ohms in both polarity directions.





2K Classic - R109 (25 ohm / 25 watt)




Enhancement Modification Recommendation:

On my Henry 2K Classis I removed the 25 ohm 25 watt resistor totally, and connected D106/C114 direct to the B- HV rail. I then added four 10 watt pulse resistors in serials with the B+ HV side as current limiter. This modification was suggested to me by Tom W8JI.








Picture of 25 Ohm / 25 Watt HV B- Resistor Removed





Added Four 10 ohm / 10 Watt Pulse Resisters in Series with the HV B+ Line



Add four 10 ohm (40 ohms total) HV Pulse Current Limit Resistors in series with the HV B+ line feeding J102 top RF deck. One 10 ohm resistor for every 1000V of the HV supply. They provide HV pulse current limiting if a voltage surge occurred on the B+ HV line due to a tube shorting or filter cap going. Highly recommend you add these resistors to any RF amplifier's HV supply.

 RCD Part Number: 175P-10R0-FBW

Ameritron Part number: 110-1100-1

Description: RESISTOR, 10 Ohm 10 Watt, 175P, 10%

P = Pulse Current Limit Option




Life is too short for QRP!!

Happy DXing



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