[Heath] Heathkit SB-240

[Randy Kaeding]

While doing a google search concerning the Heathkit SB-240, I came across a couple of blogs where some users think this amplifier was simply an SB-220 with a face-lift. Well, I was employed as a manual writer when the SB-240 was being engineered and know all about it. I even have one. Although the power supply and tank circuits between the SB-240 and SB-220 are very similar, there are several differences. One obvious was that is was styled to match the SB-104 line, which was our top-of -the-line amateur HF equipment at the time. The HL-2200 and SB-1000 amplifiers were not even a thought at the time.
 
First, the SB-240 has zero idling current, the SB-220 does not.
 
The SB-240 has an additional circuit board (approx. 6" by 6") that is mounted between the front panel and the filter stack, and a small circuit board underneath. These additional circuit boards provided the circuitry for the following features:
 
1. Pushbuttons that allowed you to select Forward Power, Reflected Power, and PEP.
 
2. SWR and overload indicators and protection. If a high SWR or overload condition was detected, the amplifier would automatically switch to standby.
 
3. A pushbutton so you could manually switch the amplifier to standby.
 
Although the amplifier was completely designed and went through the normal two proofbuild cycles, it never made it to shipment for the following reasons:
 
1. The SB-8000/SB-9000 transceiver was being designed and the SB-240 would not match the styling of this new transceiver.
 
2. The amplifier included 10 meters during the time when the 10-meter ban was eminent.
 
3. An adjustment needed to be made through a hole in the underside of the cabinet. If a regular screwdriver was used to make this adjustment, the user could come into contact with full RF power. The company didn't want to take this chance.
 
I used my proofbuild unit to make most of the 354 DXCC contacts that put me on the ARRL Honor Roll.
 
Now, does anyone want to know about my SB-2001 amplifier?
 
Randy, K8TMK
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