HERCULES From: KN4IM@N4CII.#CHS.SC.USA.NA DC POWER INPUT MODIFICATION TO TEN TEC HERCULES II 12V LINEAR AMPLIFIER I purchased a new TenTec Hercules II linear for my car. I run a full cross-band 600W packet node KN4IM-8 with KN4IM-12/T and KN4IM-10/B on "Network 105" 14.105 Mhz. Upon receiving this otherwise outstanding amplifier, I noticed TenTec cheapened out by putting 100 amps of DC through a cheap Molex connector that is only popped-in to the back panel. I looked up the connector and found it only rated at 15A per pin. TenTec uses 4 pins for + (4-#12 housewires are the biggest that will fit in the pins) and 4 pins for -. This is not only unsatisfactory, but is over the limit of the manufacturer of the connector and probably a fire hazard after the cheap pins corrode (as all Molex connectors do). I set out to correct this defect in design with a visit to my local car stereo shop. These kilowatt "boom box" stereos with their heavy switching power supplies and big current drains look to be the neatest thing that will happen to mobile ham radio for some time. The quality of the high current parts and nice looking fine-stranded power cables is outstanding. I selected 2 "power blocks" for my refit. The positive cable, a #4, bright red, fine stranded, very flexible fits just fine into a dual 50 amp, gold plated fuse block with genuine Stinger gold- plated fuses. This Stinger brand fuse block has very heavy allen screws in the large blocks to clamp down on the wires. I tinned the #4 wires before insertion to protect the strands from breakage in clamping. The negative lead, another fine stranded, #4, black cable goes into a Stinger brand terminal block that provides 4 connections to this negative lead. As there are 4 negative wires to the 4 amp sections in the Hercules II it is a perfect match with immeasurable resistance. The amp was disassembled and after looking at the cheap crimp-on push-on terminals (the kind you would use for audio speaker cables), I decided there was no use trying to salvage this corrosion prone method of making assembly fast and easy. All push-on terminals were cut off the Molex connector in the back except the wiring used for remote power control. As I had no intention of remoting the amp, I made 2 jumpers in the unused molex plug TenTec provided for the original power cables. Just copy the jumpers in the power plug they give you to hook amp to their power supply. Both the dual fuse block and the grounding block were mounted inside the cooling outlet plenum inside the back of the amp after removing the fly screen blocking free flow of cooling air. I asked TenTec the purpose of this fly screen and they said "To keep the bugs out!". This flyscreen looked like a great place for dust to collect cutting off the airflow to cool the amp so it was removed. The plenum is easy to remove by unscrewing the sheet metal screws. Use a wood block to drill and mount the blocks as the aluminum is real thin and distorts easily. Mounting the blocks in the plenum eliminates possiblility of damage to them as they are now inside the amplifier case. The #4 power cables are run through the outlet holes and terminated in soldered on terminal lugs made for them. (Gold plated, of course!) Fine strand #8 wires were run from positive and negative terminals of each of the 4 amplifiers to the centrally located control board and from the control board to the blocks in the plenum through 2 existing holes in the chassis just in front of the plenum. The wires were soldered directly to the original lugs which are riveted to the boards. I found 5 of the rivets on the boards loose from initial inspection and soldered them down properly to the board foils. The solder had evidently broken loose when the factory pushed the cables onto the tabs. My mobile uses twin 1000 CCA deep-cycle marine batteries in parallel with #0 welding cables. One battery is next to my old Mercedes diesel engine in the engine compartment and the other is inside the car in the biggest battery box I could find next to the amp. Under full load, at 600 watts output, there is no appreciable voltage drop on the Hercules II front panel voltmeter below battery voltage. Before the modification, voltage dropped a good 1.5 to 2 volts below what the battery measured under load. Only the voltage drop across the .015 ohm fusisters TenTec uses instead of a proper fuse and for balance input to the protection circuit is evident. Using a 14' long homebrew Bugcatcher with Henry Allen's biggest 6" diam coil, I am getting consistent 20 to 40 over S9 on 80/40/20 meter phone, packet, rtty and Pactor. Amazing mobile... 73, Larry KN4IM-12 mobile!