NORTHWEST
COUNTRY COUSINS
WA7NAS
WESTERN
COUNTRY COUSINS
Heathkit SB-220 Repair
Heathkit SB-220
I purchased this Linear Amplifier recently, and although it worked, it had no idle current. Also the filter capacitors were the original ones, installed in the late 70's.
My plan was to re-build the rectifier board, replace the zener diode, replace all the electrolytic capacitors and install meter protection and a glitch resistor.
I would like to thank Bryan, WA7PRC for his help and advice with this project.
Stay tuned, it will soon be on the air.
2 3-500Z tubes operating in a SB-220
Some YouTube links to the tuneup procedure for the SB-220
Here is the original capacitor bank. It has eight, 200 uF, 450 Volt capacitors with eight, 30K Ohm, 7 Watt bleed resistors.
Here is the new capacitor bank. The original capacitors were replaced with eight, 270 uF, 450 Volt capacitors and eight, 100K Ohm, 3 Watt bleed resistors.
Here is the original rectifier board. The yellow and green pair are in series with the zener diode, ZD1, and are attached to an unknown modification.
Here is the re-constructed rectifier board. The two diodes in series attached to the right side of the board are the meter protection diodes.
This is the unknown modification referred to above. This has been removed and a new zener diode has been installed, (not shown).
Here is the glitch restor placed in the B+ line in place of the original choke. It is an Ohmite 10 Ohm, 20 Watt resistor.
