[Johnson] Start of New Year

[Rodger Singley]

David,

Do you have a MFJ-259 antenna analyzer or similar?  You can use one of these to safely find output network faults and without moving a lot of stuff around.  With all of the power supplies disconnected (for safety) connect a 1/2 watt resistor from one of the tube anode connectors to ground, the resistor value should be equal to the normal operating load for the 4-400A tubes.  Leave the tubes in place so that they provide normal stray capacitance.  Connect the MFJ analyzer to the RF output terminal.  With a normally operating output network the plate and load controls should provide an indicated perfect match on the analyzer when they are adjusted to normal values.

This allows you to safely poke around in the output network without fear and to also temporarily substitute a low voltage/current capacitor for a suspected bad high power RF unit.

Do NOT forget to remove the resistor before power up or you will have a late New Years firecracker.

I used this technique to repair a friend's Viking 500 recently and I used the same method when first setting up my homebrew 160-10 meter triple 4CX800 amplifier.

73, Rodger WQ9E

-------- Original Message --------
> From: "David C. Hallam" <dhallam at knology.net>
> Sent: Thursday, January 01, 2015 8:26 AM
> To: JOHNSON LIST <johnson at mailman.qth.net>
> Subject: [Johnson] Start of New Year
> 
> I looks like I have a major project on my hands.  My Invader 2000 gave 
> up yesterday and has no output.  My first guess is the amp output 
> circuit.  The driver loads properly and the finals draw current as 
> indicated on the grid, screen and plate meters.  But, there is no 
> indication of output.  Plate voltage and the zero signal plate current 
> are OK The antenna system is OK as the receiver works but I will check 
> out the coax change over relay first.  Beyond that things get difficult.
> 
> I do not have 240V at my garage workshop and the Invader is too heavy 
> for me to move anyway.  Just had arthroscopic surgery on my shoulder.  
> At 60+ lb for the transmitter and 100+ lb for the power supply I 
> couldn't manage it anyway.  I have to completely tear down my operating 
> desk and move test equipment in from the garage.  Not a happy start for 
> the new year.
> 
> David
> KW4DH
> 
> -- 
> There are two possible outcomes: if the result confirms the hypothesis, then you've made a measurement.
> If the result is contrary to the hypothesis, then you've made a discovery.
> Enrico Fermi
> 
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