Why are there upgrades?
Lunar-Link Systems has continually enhanced and improved its products. Some of the enhancements can be installed in existing products, while other improvements would require such extensive modifications that it is not practical to install them. Below are some of the more significant upgrades that are applicable to older products.
LA-200 and early manufacture LA-22 Input circuit.
The new cathode circuit replaces the original 1/2wv high Q tuned line with a low Q T network. The new circuit reduces driver power, is easier to tune, has broader frequency coverage and is less susceptible to damage if the amplifier is over driven. With the new circuit drive power for 1,500 watts output is typically less than 40 watts.
LA-200 and early manufacture LA-22 Low Pass Filter Capacitors.
The revised capacitors further reduce harmonic emissions and reduce the possibility of damage to the capacitors should the amplifier be accidentally run at full power without an antenna connected.
LA-200 and early manufacture LA-22 Plate Stripline update.
A number of small changes have been made to reduce the possibility of HV arcing should the plate compartment become coated with dust and dirt.
LA-70B, LA-135, LA-200 and early manufacture LA-72, LA-12, LA-22 Plate Load Capacitor.
The Plate Load capacitor on earlier models was made from half hard brass. Over time the flapper can take a set which reduces the plate load adjustment range. A revised capacitor made from spring temper phosphor bronze both has a greater initial plate load adjustment range and it will not take a set over time.
LA-135 and early manufacture LA-12 Input circuit.
The new cathode circuit replaces the original 1/2wv high Q tuned line with a low Q T network. The new circuit reduces driver power, is easier to tune, has broader frequency coverage and is less susceptible to damage if the amplifier is over driven. With the new circuit drive power for 1,500 watts output is typically less than 45 watts.
LA-70B and early manufacture LA-72 RF output stub.
The safety choke was replaced by a ¼ wavelength stub. The stub both reduces even harmonics due to it's notch characteristics but also reduces high frequency harmonics by eliminated stray coupling from the choke.
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LA-70B and early manufacture LA-72 RF output low pass filter.
A low pass filter was added to reduce harmonic emissions. Although the FCC does not have spurious emissions requirements for 70cm equipment, the LPF was designed specifically to reduce the 3rd harmonic (1296 MHz) to reduce interference to 23 cm stations in multi-op stations.
LA-200 and early manufacture LA-22 neutralization.
The contact finger pattern of the grid collets was changed to move the self neutralizing frequency to 144 MHz. The update improves plate efficiency by about 2% and slightly reduce harmonic emissions.
LA-135 and early manufacture LA-12 neutralization.
The contact finger pattern of the grid collets was changed to move the self neutralizing frequency to 222 MHz. The update improves plate efficiency by about 2% and slightly reduce harmonic emissions.
LA-70B, LA-135, LA-200, LA-72, LA-12, LA-22 heater voltage test points.
Test jacks were added to the rear panel to provide and easy means to measure the tube heater (filament) voltage without removing the bottom cover.
LA-70B, LA-135, LA-200, LA-72, LA-12, LA-22 heater voltage adjustment access plate.
An access plate was added to the bottom cover to provide and easy means adjust the tube heater (filament) voltage without removing the bottom cover.
LA-70B, LA-72 & LA-72A without option -106 heater voltage relaxation circuit.
Adds a circuit that reduces the tube heater voltage on transmit to compensate for cathode back heating which occurs at UHF frequencies. This upgrade is primarily for continuous carrier operation such as JT digital modes..
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