[Heathkit] SB-220 on 120 volts

[Kenneth G. Gordon]

On 12 Feb 2008 at 22:36, kc7hkp at comcast.net wrote:

> I Guys
> I just got my heathkit SB-220 Going for the first time since owning it
> for many years, Put in a set of used Emiac 3-500z tubes, We used 220
> volts at a friend place, I do not have 220v yet, only 120, I am getting
> a bid to have 220 installed by the way. Would it be dumb to use
> 120volts if 220 volt installation is beyond my expense allowance?

Yes, if you expect to get full output from that amp. 

If you run it at much more than, say, 750 watts input for SSB, or a KW for 
CW, your line voltage will sag pretty badly.

If you have the amp on the same circuit as the rest of your shack, or even 
a significant part of it, you will more than likely blow the breaker or fuse 
connected to that circuit when you hit full-power peaks.

You COULD use a single, 20 amp 120 V circuit which would have to have 
nothing else on it but that amp (a "dedicated circuit"), and the wiring, 
which should be #10 wire, between the amp and the breaker or fuse panel 
would have to be kept short.

Most homes have #12 wire going to the plugs, and many older ones have 
#14. #10 wire is good for 30 amps, #12 is supposedly good for 20 amps, 
while #14 is good for 15 amps maximum.

However, even if you did use a dedicated 20 amp 120 V circuit, most of 
the lights in the circuits connected to the main panel will blink on SSB 
peaks, or CW keying, sometimes pretty badly.

If it were me, I wouldn't do it permanently.

I use an SB-200, which at max has about 1/2 the power input/output as 
your SB-220. I have a dedicated 120 V line attached to it, mainly because 
I have been too lazy to wire in a 220 V socket at the operating bench (I 
am a qualified electrician). And when keying my combo at 1200 watts 
PEP INPUT on SSB, or 1000 watts INPUT on CW, I get blinking lights in 
the shack on peaks, and I don't hold the key down very long.

My shack, exclusive of the lights, is fed with a single #10 3-wire, 2-circuit 
line from our 200 amp panel, and the breaker is rated at 30 amps. The 
distance to the panel is about 18 feet. The #10 feeds a separate two-pole 
safety swich with a BIG noticable, and well-marked handle. I then connect 
two #12 Romexs from separate 20 amp fused connections at that switch 
to feed the operating bench. One line is for the amp alone, and the other 
line is for the rest of the gear.

I repeat: if I had an SB-220, I either wouldn't run it on 120 V, or if I had to, 
I wouldn't load it beyond about 750 watts input, or about 350 mA at 2000 
VDC.

According to the manual, if you MUST use a 120 V circuit, it should be 
fused at 20 amps, wired with #10 wire, and ONLY the amp should be on 
the circuit. Then you would have to put up with the blinking lights...which I 
don't particularly mind... :-)

BTW, the SB-220 is an excellent amp.

Ken Gordon W7EKB