Sb-220 or sb-221

[153]

I am looking to purchase a Heathkit SB-220 or SB-221 for 10 meter use. Which would be the prefered? And why?

[PONY EXPRESS]

Both basically the same amp except on the SB 221 10 meters was an optional kit .The SB 220 had 10 meters standard
So the SB 221 is the newer version in as it was produced after teh FCC implemented the 10 meter amp rules .

[153]

will it work ok on am?

[PONY EXPRESS]

Wasnt designed for AM use but people do it and burn up tubes

[Red Warrior]

Neither of these amplifiers were designed to operate on AM. They were designed for and work perfectly on SSB. Neither the power supply nor the tubes will withstand 100% duty cycle (AM) for very long and repair is VERY expensive.

Better to use your hard earned cash on an amplifier designed for full duty cycle on AM.

From the SB-220 User Guide.

"Do not use the SB-220 on AM or FM modes—it is not designed
for these modes, and using them will significantly exceed the
amplifier’s ratings and surely cause excessive damage."

[153]

OK What kind should I look for? BRAND AND TUBE

[Red Warrior]

An Ameritron AL-800 with the 3CX800A7 tube. Just about any amp with a metal tube will do the job.

[KKD3088]

Neither of these amplifiers were designed to operate on AM. They were designed for and work perfectly on SSB. Neither the power supply nor the tubes will withstand 100% duty cycle (AM) for very long and repair is VERY expensive.

Better to use your hard earned cash on an amplifier designed for full duty cycle on AM.

From the SB-220 User Guide.

"Do not use the SB-220 on AM or FM modes—it is not designed
for these modes, and using them will significantly exceed the
amplifier’s ratings and surely cause excessive damage."

Although that is correct, you can run the SB-220/SB-221 conservatively at 200 watts carrier output on AM and it will run fine. Load it up for maximum output, then (very important) back off on the RF drive from your exciter until you have 200 watts carrier output. This will also allow for over 100% positive modulation peaks. You will not have distortion on your audio which is very common when someone tries to get more output from an amp than it is designed for. Also, I recommend buying the Harbach fan kit for the SB-220 that will provide 30% more cooling on the 3-500Zs which is needed when running AM. If you run the amp at higher than 200 watts carrier, you will cook the amp for sure.