So I have accepted the challange to figure this out on my own and hopefully with all your help, be successful. I also live far enough away from everything that shipping would be an arm and a leg. I appologize for all the questions, but where I am at there is no one capable to work on this sort of equipment. There are a couple setting to set the bias to, between -35 to -50 (is this per tube?) or -400 (all four combined -100 per tube)? Your thoughts. Which meter is to be adjust, the AMP or KV meter? Now looking at the face of the meter, it suggest that these are not premium grade meters so I assume accuracy is not the greatest. The knob on the bottom right is the bias control. The amp have two meters on the front, one is a KV meter and the other is a AMP meter. What is the impact or reason for removing the resistors? With this damage the amp not having this protection? It is a solid braid lead from each tube to the capaciator. The amp I found on the web does not use the resistors from the tube clamps to the door knob capactor. I searched the web for pictures of the amp and found some which I will include. What is the reason for this and is this a shunt resistor as someonen else mentioned? Looking at the resistors, they have been overheated pretty bad and I guess the guy who had it was going to replace them. The resistors have a single wire wrapping three times around the resistors and soldered on both ends. Not sure what the watt rating is, thinking it may be 2-5 watt rating. The resistors are 10 ohm, 5% carbon composition resistors. I was told these were soldered to the tube clamps, all four tied together and a single lead went to a door knob capaciator. When the amp was acquired it came with a bag with four resistors in it. I was told this is fine for the 4CX250B tubes. The radio to be used will have a 40 watts peak modulation drive. This amp (what I was told) uses a 4-5 watt carrier. Let me see if I can answer some questions for you all. The bias current would be the same if it were grid driven or cathode driven. I'd keep all four tubes at or below 200 ma total zero signal bias current. If I were you I would put the amp in class B at no more then half the AB1 bias current. Adding 800 watts of DC bias dissipation on the plates for AB1 may well push the amp over the edge and start burning things up. Most CB amps are already stressed out to the max to begin with. If the plate voltage is more then about 2000 volts under load or you use the amp on AM, I would seriously consider a lot less bias on these tubes. This gives you the 100 ma per tube (assuming they are matched) for class AB1. If you're lucky enough to have an accurate front panel plate current meter, the bias would be set at 400 ma with the relay keyed and no drive applied.
#VARIABLE BIAS VS FIXED BIAS GUITAR AMP FULL#
So, Hit and Run, do tell us what the drive requirements are on this amplifier for full output? Unless the amplifier has a CALIBRATED plate current meter, aligning the bias for a particular class of operation would involve having to measure dangerous points within the amp. For 1000 watts plate dissipation in triode configuration you might as well just use a pair of 3-500Z's.
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