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Author Topic: Gonna need a bigger boat !  (Read 479 times)
N4MQ
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Posts: 319




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« on: May 22, 2019, 05:26:30 AM »

I have restored a HF thunderbolt thats in daily operation on 3705 [ 1885 kc in the winter ].  I have a Invader 2000 thats been clean chassis rebuild / repainted - new dial - and restored with the 200 watt section on the air, just need to finish the homebrew HV power supply check out to get AMP section on the air.

Just picked up ( slowly ) two more invader 2000 and the factory outboard power supply.  Never saw one before and its complete, yeah.

Seems Johnson high power rigs are like potato chips or kittens - - you cant have just one.  But Iam set for a while as far as projects.  If others are restoring the invaders I would like to communicate with them, enjoy Woody
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WA2CWA
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« Reply #1 on: May 22, 2019, 12:49:20 PM »

What mod does the Thunderbolt have to get it on 160M?

Pete, wa2cwa
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N4MQ
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Posts: 319




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« Reply #2 on: May 23, 2019, 05:12:32 AM »

I used a spdt russian 24 antenna relay to switch in a HV disc cap from france (?) that was about 160pf AND to un short the additional 12 Uhenry coil I added in series  with the tank coil. Works great.

Now I went one level higher by re wiring the RES  resistive input position on the band switch to switch in a tuned circuit for the grid tuning.  This was done by adding a capacitor to the input tuning circuit.  Band switch now has the lowest position enable 160 meters.

 To make this all clean the band switch shaft was cut about 4" shorter and a rotary switch was added in line with the band shaft.  This provides the switching circuit to operate the russian relay fed off a voltage doubler fed from the 6.3 filament and 5 volt rectifier filament voltage the is no longer used due to plug in solid state rectifiers.  I took the rectifier tubes and crushed/removed the glass to repurpose the sockets for 3 amp diodes, thus the spare filament supply.

The HV power supply is off chassis to make the thunderbolt liftable, now some 60 pounds.  The HV circuit is keyed by the microphone/transmit switch so the HV is not present during stand-by.  The bleeders that draw some 225 watts are deep sixed and the standby power is very low during non transmit periods, saving heat and giving back that power from the supply supply for plate current. 

I use a contactor to key/switch the power transformer on with a 660 watt ceramic heater in series for soft start.  The cone shaped soft start 660 watt resistive heater is bypassed by a solid state relay when the HV reaches about 60 % of the 3000 volt level.  This method insures the start up is swift and when I have a faulted -shorted final, the soft start circuit is protected by a "soft start fuse".

Some info here:   https://sites.google.com/view/thunderbolt-amplifier-site/home

Enjoy Woody N4MQ
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