Steve, VR2XMQ gave me the SB-220 when the time he moved QTH. The amplifier was modified to six meter by one of the ham in the United States. However, the amplifier experienced with problem since it arrived. In the first instance, the HV meter was damaged in shipping and flash over when switch on, which finally proved one of the 3-500z have problem. The outlook of the amplifier was bad, most of the screws are rusted and internal wiring is in a mess, overall it is not a professional workmanship.
The amplifier was sit there for sometime and few weeks ago, I decided to re-build the amplifier and make it ready for cycle 24 for some DX in the magic band.
Here below are the major improvements:
1) repainted the power and filament transformer and inside chassis
2) replace most of the rusted screws
3) replaced all eight HV filter capacitors to 270uf 450V 105 degree C
4) replace the HV rectifier board completed with eight 1N4007, which used as the 5.1V bias zener diode
5) replace two panel meters
6) replace the load capacitor
7) add soft-start and soft-key
8) replace the burnt safety choke (8 mm Teflon rod with approx. 60 turn of SWG 22 wire.)
9) replace one 3-500z
10) refine the input SWR
11) tidy up all internal wiring
With AC mains supply at 207V, it gave out 900W with 100W drive. It can be more if AC voltage up a little bit. Now it is a 100 percent working amplifier and ready to go.
The amplifier was sit there for sometime and few weeks ago, I decided to re-build the amplifier and make it ready for cycle 24 for some DX in the magic band.
Here below are the major improvements:
1) repainted the power and filament transformer and inside chassis
2) replace most of the rusted screws
3) replaced all eight HV filter capacitors to 270uf 450V 105 degree C
4) replace the HV rectifier board completed with eight 1N4007, which used as the 5.1V bias zener diode
5) replace two panel meters
6) replace the load capacitor
7) add soft-start and soft-key
8) replace the burnt safety choke (8 mm Teflon rod with approx. 60 turn of SWG 22 wire.)
9) replace one 3-500z
10) refine the input SWR
11) tidy up all internal wiring
With AC mains supply at 207V, it gave out 900W with 100W drive. It can be more if AC voltage up a little bit. Now it is a 100 percent working amplifier and ready to go.
