Original "basket case" Alpha 76PA amplifier. The RF input is a BNC connector, and the RF output is an SO-239. Rear panel of ampifier, showing ICE low-pass filter, ALC threshold adjust, and r.f. Six Meter Linear Amplifier, showing new front panel and cabinet (above), and original Alpha 76PA junker (below). All interconnect wiring in the RF compartment uses coax or shielded wire. I used the original blower, which is nearly perfectly matched to the cooling requirements of the 3Cx800A7 and very quiet. The RF sampling circuit (for the wattmeter), ALC, relay and control circuits are all new. The new silver-plated tank coil was fabricated from a section of the orignal Alpha 76PA plate inductor. A red panel lamp (above the plate current meter) lights during warmup and when the amplifier is on-line.Ĭonstruction Details: An alodized aluminum cover plate for the 3CX800A7 tube socket was fabricated from a piece of the old front panel. A plate overcurrent relay trips the amplifier off-line if Ip exceeds 2 Amps. The original power supply was left intact, except for a new 14 VAC filament transformer, a 28 VDC bias and control voltage supply, a 3 minute "warmup" timer, and a grid overcurrent LED warning circuit. An ICE Model 426 low-pass filter is permanently attached to the rear panel to improve harmonic suppression.
HOMEBREW AMPLIFIER SERIES
It is in series with a 15 uH VHF supressor choke (13 turns # 20 wire, close wound). The 6.5 uH plate choke is 40 turns, space-wound on a 3/4 in.
The plate tank circuit pi-network inductor is 0.36 uH and consists of 4 turns of 3/16 in. Design parameters for the input network are 0.66uH for L1 and L2, and 27 pF for the arm capacitance. dia) forming the bridge of the "T," and a 10-75 pF variable capacitor for the arm. The input network is a T-network, with two inductors (8 turns, 1 in. long) isolates the cathode and filaments of the 3Cx800A7. A trifilar-wound filament choke (6.4 uH, 10 turns on 1/2 in. The rebuilt amplier uses a single Eimac 3CX800A7 triode, and features vacuum antenna relays, new metering and control circuits, electronic bias switching, and new forward/reverse power measuring.Ĭircuit Details: The circuit is a conventional cathode-driven (grounded grid) design. deck components were discarded, except the tune and load capacitor, the former being rebuilt (using the few remaining unmelted plates!) to cover 10-30 pF. I began construction by scrapping the front panel, cabinet top and side panels, and stripping the r.f. Fortunately, blank panels and cabinet parts were available from the original cabinet supplier. The meter was defective, and an extra hole had been drilled in the front panel. The original Alpha amplifier was missing its two 8874 tubes, and the bandswitch and tuning capacitor had been badly arced and melted. This item can be shipped to Canada, United States.This homebrew six-meter linear amplifier started off life as a "junker" Alpha 76PA h.f. The seller is "palco123" and is located in Gull Lake, Alberta. This item is in the category "Consumer Electronics\Radio Communication\Ham, Amateur Radio\Ham Radio Amplifiers". The item "Hf Linear Power Amplifier for sale 2-30 mhz Homebrew 4 pill brand new build" is in sale since Saturday, August 14, 2021. This is my self-supporting hobby and I dont look for a huge profit. PEP output will depend on your particular radio. Reports at the receiving end were favourable. I had a friend use this unit in his mobile for a couple of days and had no problems. More than sufficient heat sink, hi-flow cooling fan and vented chassis assure that this unit runs reasonably cool. Ive been building linear amps for many years (Im a retired Electronics Tech). Hf linear amplifier for sale 2-30 mhz Homebrew 4 pill brand new build. Hf Linear Power Amplifier for sale 2-30 mhz Homebrew 4 pill brand new build
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