Heathkit Sb-220 Linear Amplifier With Manual For SaleTaken from the Heathkit SB-220 assembly and installation manual:The Heathkit Model SB-220 Linear Amplifier is a completely self-contained, table top, grounded grid, linear amplifier. It is designed to operate at the maximum amateur power limit on SSB, CW, and RTTY. Its styling matches the Heath SB series of amateur equipment.The Amplifier is designed to be used with exciters which deliver 100 watts or more output. It can be used with less driving power, but will give a lower output.A broad-band, tuned input circuit for each band feeds the two Eimac 3-500Z triode tubes connected in grounded grid configuration. The tube are biased beyond cut-off in the receive mode, and zener-regulated bias controls the idling current in the transmit mode. The tubes are cooled by a fan.An ALC circuit develops negative voltage to be fed back to the exciter to reduce its gain when the Amplifier is overdriven.The antenna changeover relay is normally actuated by exciter relay contacts to place the Amplifier in the transmit mode.The Amplifier can be operated from either 120VAC or 240VAC 50/60Hz lines and can be easily changed from one to the other. Operation from a 240 volt line is recommended. Each side of the line cord is equipped with a circuit breaker to protect against overloads.An important feature of this Amplifier is that it can be tuned up at the one kilowatt limit and can then be switched to operate on SSB at two kilowatts P.E.P. input. As the switching changes both the voltage and current to the final tubes, the impedance remains the same and no additional adjustments of tuned circuits is required.The tubes are "instant heating" types, and transmission may be started as soon as the Amplifier is switched on (after tune-up).Here is a full legal-limit Amplifier that can take its place on your operating table and give you years of trouble-free pleasure. This Amplifier has a commanding Coverage . . . . . . . . . . 80, 40, 20, 15, and 10 meter amateur bands.Driving Power Required . . . . 100 watts.Maximum Power Input . . . . . SSB: 2000 watts CW: 1000 RTTY: 1000 watts.Duty Cycle . . . . . . . . . . . . . . SSB: continuous voice CW: continuous (maximum key-down 10 RTTY: continuous (maximum key-down 10 minutes).Third Order Distortion . . . . . -30dB or better.Input Impedance . . . . . . . . . . 52 ohm unbalanced.Output Impedance . . . . . . . . . 50 ohm SWR 2:1 or less.Front Panel . . . . . . . . . . . . . . Meter CW/Tune -- Plate Multi-meter (Grid mA, Relative Power, High Voltage).Rear Panel . . . . . . . . . . . . . . . Line cord (Note this unit is presently wired for 120VAC Circuit breakers (two Antenna Relay ALC RF Input GROUND RF Output (SO-239).This unit is presently wired for 120VAC operation but can be changed to 240VAC if required. It was last fired up about 10 years ago and tested with a Heath Cantenna dummy load. All functions worked fine at that time, however the unit has not been powered up since and is being sold "as-is" since I have no way to test it again. The extra black wires coming out the back grille area (see pics) are wired in parallel with the internal fan, so you could drive another external AC fan from these for additional cooling. As with all user-built products, it would be beneficial to spend some time cleaning and inspecting the internals, deciphering any mods that may have been made, and possibly powering it up slowly with a variac to allow the unit to "acclimate" since it hasn't been used for so long. It appears to have someone's (Harbach?) parasitic suppression mod installed (see pics) however I cannot be 100% sure as I don't have a mod to compare it with. It may or may not have other Harbach (or others) mods as well (see pics). This is a very clean unit with no discoloration on either of the 3-500Zs that I could see, and the red "Eimac 3-500Z" printing on each tube is perfectly readable and not discolored. The safety interlock appears to be disabled however it looks easy to make functional again if desired. This interlock was designed to short the high voltage to ground in the event the chassis' top cover was removed to provide a safety feature to the user. As internal voltages can reach upwards of 3KV, this unit is not a toy and should be handled by experienced personnel familiar with how to handle high-voltage equipment. FOLLOW ALL WARNINGS PRINTED IN THE ASSEMBLY MANUAL! It is included.This unit is very heavy and will be carefully packed and double-boxed for shipment. At the buyer's option I will remove the finals and pack them to be safely shipped separate from the main box at no extra charge. That can be decided via email after end of sale.
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