User Guide

3
When you operate your linear amplifier, you will probably find that the plate voltage reading is
much higher than before. This is not really the case. The voltage is the same as before, but you
are now reading the true voltage. You may notice a slight reduction in the idling plate current of
your SB-220. This is because the new board produces 6.8V of bias for the 3-500Z tubes, rather
than the 5.1V provided by the original Heathkit design. This will lower the heat produced by the
amplifier during voice lulls, but will not materially affect the linearity at high power levels.
RM-220 RECTIFIER & METERING BOARD
HARBACH ELECTRONICS
Jeff Weinberg – W8CQ
468 County Road 620
Polk, OH 44866-9711
[phone]
http://www.harbachelectronics.com
[e-mail]
PARTS LIST
D1 & D2 5-1N5408 (3A 1000 PIV)
D3 – D6 1N5408 (3A 1000 PIV)
D7 8-1N4005 (1A 600 PIV)
R1 1Ω 3W 1%
R2 3600Ω ¼W 1%
R3 0.82Ω 3W 5%
R4 14-1MΩ ¼W 1% IN SERIES
R5 5600Ω ¼W 1%