Some Sb-220 Questions.

Hi I have a few questions for the SB-220 owners out there.

1st: Looking at pictorial 4-5 in the manual it shows a brass spring like device touching a metal shaft. Is this a type
of HV interlock? See Pic attached. Also if one were to remove the perforated inner lid and apply power would it go poof? Snap crackle pop?

2nd: I read where the input coils have some problems matching modern rigs. Is this true? If used will it show high SWR
on the radio? I know they can be tweaked just wanted to be sure.

That's it for now if I have any other questions I know where to ask them.

Thanks folks I appreciate any and all input.

 

"1st: Looking at pictorial 4-5 in the manual it shows a brass spring like device touching a metal shaft. Is this a type
of HV interlock? yes, it is designed to help protect those that shouldn't open the covers. Also if one were to remove the perforated inner lid and apply power would it go poof? Snap crackle pop?" It wont; you might.

"2nd: I read where the input coils have some problems matching modern rigs. Is this true? If used will it show high SWR
on the radio? I know they can be tweaked just wanted to be sure." Anything besides a 50 ohm resistive load will show up on your radios swr meter. Yes, you many want to fine tune the input filters, but it's not simple. May not have to.

 

Hey fellow Floridian! Greets. Regarding the picture attached any idea what the red stuff in on the plates of the large cap at the top of the picture? Also I would guess that the 2nd question is most like done already. These amps are kind of old and have been around for a while.

Yeah I might go snap crackle If I defeat it touch the wrong place....Not a good ending or really bad pain as I fly through the wall!!! LOL

 

The red stuff is where someone added anti-corona material to those plates. Heathkit didn't do that, somebody else did.

No harm. However it might indicate that a previous owner experienced an arching problem (which really shouldn't happen).

I built an SB-220 from a kit 43 years ago and sold it about 15 years ago and it's still going strong with the original Eimac tubes. They're strong amps if you keep them down to the original design limits, which was 1 kW DC input power as they were rated. Some try to push them to 1200W PEP output power, which was not the design intention, and that can cause various failures.

The HV interlock can easily be defeated but that's not recommended.

Some things I disliked about the SB-220:

-The plate TUNE tunes way too fast on the higher bands, making peaking it a bit of a challenge; I always added 6:1 planetary dial drive reductions to mine and those I've serviced for others. (This is not a problem on 80-40m, it becomes more of a problem on 15-10m.)

-Of course the keying circuit is very obsolete and almost everybody has to revise that for low voltage positive polarity keying.

-The cooling is a bit minimal, although was sufficient for the original ratings (1 kW DC input power, which would yield maybe 600W PEP output power). When "pushed" to what it can really do, it's a good idea to increase the cooling.

-The power supply can't handle high duty cycles, like RTTY.

But I think it's a great design in most respects, and there's thousands of them on the air.

 

Thanks for the input. It is highly appreciated. Have no intention to do RTTY so that is not a problem. So it is actually a 1KW amp then? Now my dilemma keep my Al-572 or sell and get the SB-220. Or keep both! I do like the idea of a 6:1 vernier added to the plate control. My AL-572 has those and makes it real easy to tune up. I was offered a price that is hard to beat. But not overly cheap though. Again thanks

 

They're both fine, but unless you have two stations at two different locations, I don't know why you'd need two amps.

The AL-572 works 160m, which the SB-220 does not. It's also more modern. Personally, I'd dump the 220.

 

A correction to my previous post: the HV interlock will short out the HV supply when activated. I think this will then fry the current limiting resistor (as it is designed). So if you have to run it with covers off --DANGEROUS--, place a plastic spacer in between the contacts.

 

Mine does about 1350 out on 80 meters. But I am not one of those rag chewers that go on, and on for 5-10 minutes per transmission, either, so I am not worried about overheating. Mine has a new set of RF parts 3-500ZG's.

 

The SB-220 was rated at 2KW PEP INPUT and will easily run 1200W out, but it is probably happier at 1KW out.

 

I am pretty conservative with my amps. When I had an Al-811 I usually ran it at between 450-500 watts.