Hello all,
Is it possable to modify a saber convertacom amp from 150.8-174.0 Mhz to 144.0-174.0 Mhz. Or are mods even needed? Any info would help.
Thanks,
kc0qgl
any saber convertacom amp mods poss.?
Moderator: Queue Moderator
Convertacom amps....modifications.
I suspect you are referring to the silver boxes with the 4-pin Jones plugs.
Yes, those amps can be tuned down very simply to the 2 meter band with some different caps and inductors, and if the amp uses tuned lines, you can solder 'pads' to these in strategic locations to get the input and output inductancesand reactance in the proper range.
Cut some shim copper of .004" in rectangles(about 8 pcs.) and get several toothpicks and super glue and glue several of these strips to the toothpicks, and while transmitting into a proper termination, and using a good SWR bridge, you can find the proper points to solder the pads with a drop in the output SWR by sliding the copper strips along the input and output matching networks...a drop in current draw and SWR should be noticed, solder a strip there.
Repeat the process until you obtain the lowest reading with the highest power transfer and LOWEST current draw.
If coils are used, follow the dimensions that are on the board and wind a few with 1 to 3 turns more, then solder it in place and take a reading.
If little to no change is seen, you will probably have to add capacitance to the output and input circuit, and you will probably have to remove the green enamel that may be on the traces to get to the bare copper foil.
Tuning these amps is not difficult and should be able to be accomplished in one evening.
Use step by step verification, and take readings along the way.
Input current draw is very important to prevent thermal runaway.
When adjusting capacitances, your best bet is to always use clad mica caps for transmitting as they are designed for use in high RF fields and don't break down with the RF current either.
They are known as: UNELCO, or Underwood Electronics Company.
The copper 'pads' are used to add inductance to the input and output networks, and match the transistor's input and output impedance for maximum power transfer and minimal current draw for rated output.
You NEVER want to draw more than 10 amps with a 40 watt amplifier, something will blow...the P.A device!
You will have several measurements to conduct while tuning the amp:
Input SWR
Output SWR
Current draw
RF input power
RF output power
Yes, those amps can be tuned down very simply to the 2 meter band with some different caps and inductors, and if the amp uses tuned lines, you can solder 'pads' to these in strategic locations to get the input and output inductancesand reactance in the proper range.
Cut some shim copper of .004" in rectangles(about 8 pcs.) and get several toothpicks and super glue and glue several of these strips to the toothpicks, and while transmitting into a proper termination, and using a good SWR bridge, you can find the proper points to solder the pads with a drop in the output SWR by sliding the copper strips along the input and output matching networks...a drop in current draw and SWR should be noticed, solder a strip there.
Repeat the process until you obtain the lowest reading with the highest power transfer and LOWEST current draw.
If coils are used, follow the dimensions that are on the board and wind a few with 1 to 3 turns more, then solder it in place and take a reading.
If little to no change is seen, you will probably have to add capacitance to the output and input circuit, and you will probably have to remove the green enamel that may be on the traces to get to the bare copper foil.
Tuning these amps is not difficult and should be able to be accomplished in one evening.
Use step by step verification, and take readings along the way.
Input current draw is very important to prevent thermal runaway.
When adjusting capacitances, your best bet is to always use clad mica caps for transmitting as they are designed for use in high RF fields and don't break down with the RF current either.
They are known as: UNELCO, or Underwood Electronics Company.
The copper 'pads' are used to add inductance to the input and output networks, and match the transistor's input and output impedance for maximum power transfer and minimal current draw for rated output.
You NEVER want to draw more than 10 amps with a 40 watt amplifier, something will blow...the P.A device!
You will have several measurements to conduct while tuning the amp:
Input SWR
Output SWR
Current draw
RF input power
RF output power