SB 220

[Atlasta]

I have an opportunity to obtain an SB 220. There is much information to be found online about these amps and I've read through a bunch of it. What I can't find is a definitive answer on how well these old boxes tune up on 11.

Therefore I have a few questions for the more learned out there

1) How well do these amps work on AM? I'm primarily an SSB operator but occasionally like to rag chew on AM. I tend to be a bit long-winded in my transmissions and was wondering how well the amp will hold up.

2) Is the 3-500z truly an 'instant on' tube? The lack of a standby switch on the SB 220 concerns me. I figure I can control the output with the drive so a 'hi/lo' switch isn't necessary.

3) Is there any significant benefit in making it into a mono-bander?

4) Will a Cobra 135 and a sweep tube driver amp key the thing? Or are additional mods necessary?

5) On this website: Circuit Improvements for the Heath SB-220 Amplifier the author speaks of a problem with the 3-500 going into VHF parasitic oscillation causing the tubes to short out. Is this really a frequent problem?

I've been searching for a larger amp for a while. Being a tube geek I'm not interested in solid-state amps. Comparing the costs of a 'real' amp vs. the sweep tubes I've been using, the 'real' amps come out ahead in the long run. I understand that those 3-500s can last for decades if not abused. I'm getting good life out of my old sweepies but the cost of retubing something like a Phantom really gives one pause which is why I'm looking at the 220.

No doubt the 220 will provide a cleaner signal than the sweepies. In every comparison I can think of the 220 wins hands down. This should be a no-brainer choice but it's actually keeping me awake at night.

Advice, comments and complaints are welcome.

 

[Crusher]

I can't remember, but I think mine might have had a footpedal. Been a few years. You can drive it with a barefoot radio if you like. Those amps like about a 300W dead key and let it swing. The transformer is not made for much higher continuously. If you do, you can risk killing the plate transformer. Yes it can be made a monobander if you wanted it to be. But it will work well as is.

 

[GnG8d]

What I can't find is a definitive answer on how well these old boxes tune up on 11.

They tune up fine.

1) How well do these amps work on AM? I'm primarily an SSB operator but occasionally like to rag chew on AM. I tend to be a bit long-winded in my transmissions and was wondering how well the amp will hold up.

AM is fine as long as the power supply has been updated and you don't want to key more than 500 watts ...... 300-350 watts would be more realistic.

2) Is the 3-500z truly an 'instant on' tube? The lack of a standby switch on the SB 220 concerns me. I figure I can control the output with the drive so a 'hi/lo' switch isn't necessary.

The 500z cathode is directly heated, but I'd still give it a minute or 2 before keying it ....... which BTW needs to be keyed manually in the SB220 and has no "standby".

3) Is there any significant benefit in making it into a mono-bander?

A handful of watts maybe and a little cooler operating temp, but nothing significant.

4) Will a Cobra 135 and a sweep tube driver amp key the thing? Or are additional mods necessary?

As with any amp, it's all about the carrier and level of modulation.

5) On this website: Circuit Improvements for the Heath SB-220 Amplifier the author speaks of a problem with the 3-500 going into VHF parasitic oscillation causing the tubes to short out. Is this really a frequent problem?

The "author" has "items" for sale. Lets not try and make a silk purse from a pigs ear, it's a 40 year old amp.

Comparing the costs of a 'real' amp vs. the sweep tubes I've been using, the 'real' amps come out ahead in the long run.

Sweep tube amps aren't "real"?

I understand that those 3-500s can last for decades if not abused. I'm getting good life out of my old sweepies but the cost of retubing something like a Phantom really gives one pause which is why I'm looking at the 220.

I'm pretty sure sweep tubes have lasted for decades as well.

No doubt the 220 will provide a cleaner signal than the sweepies. In every comparison I can think of the 220 wins hands down.

I'd like to see that comparison. The SB220 runs a pair of 500z's in class B bias, but I've seen sweep tubes run on up into AB1 and AB2 and probably even higher.

This should be a no-brainer choice but it's actually keeping me awake at night.

It is a no-brainer. If it's a good deal and you want it, buy it. As long as it hasn't been beat to death, and you don't pay too much, you can always get your money back.

 

[Atlasta]

When I wrote about a 'real' amp I was actually referring to the tube itself.

It's a good deal but not a great one.

Think on this more I must.

Thanks!











So for

 

[wavrider]

Good amp, I got one in the shack.

A lot of info on the net.

Not designed for AM but will work, keep it on the low voltage setting, no more than 250 to 300 watt carrier and do not drive more than 100 watts into it.


If upgrades have not been done then definitely need to replace the HV filter caps.

VHF parasitic? Not really the design is a rather good design and has stood the test of time.

A decent clean 800 to 1KW watts out and will give you good service if not abused.

If it is a good deal then jump on it. If it is coming from 11 meter service then make sure you check it out thoroughly, band switch and tuned inputs are some of the weak points if they have been over driven in AM service.

 

[W5LZ]

The Heath Kit SB-220 was a popular amplifier in it's time, it worked well. There are a few things to remember about them though. Probably the biggy is that 99.9% of them were built by amateurs. That means that the quality of the build ranged from one extreme to the other, good/bad. Except for very few exceptions all of them have probably been rebuilt at least once, and repaired several times. The things are almost 40 years old. They were designed and produced with several aspects that are different now. The biggy with that is that they were rated by input power, not output power, so do not expect the wattage normally claimed for them.
The worst part of an SB-220 is the power supply, which is/was barely adequate. The supplied transformer is too small for thing, it was worked at it's top end, 'full bore', all the time to get it's rated input power <-- not output power ratings.
They were nice 'desk top' amplifiers. Certainly not as 'perfect' as some believe, but were affordable by the average user.
- 'Doc

(Wish I had back the ones I had. Not that I think they are so great, but at something like 3 - 4 times their original selling price, I'd sell'em and get a new amplifier!)