HeathKit sb220

[four6zero]

Just purchase sb220 from an estate sale of widow, I was told that I needed a switch to kick the amplifiers relay on?
I always thought that the watts from the exciter will trigger the sb220 on..
What is it that I dont know, and what do I need to know.
If I need a switch, what does it hook up to? and is the switch called a switch or a trigger switch?
Oh yeah, I'm new to this..
Any help will be appreciated..

 

[Triple J]

You can buy a foot keyer to key the amplifier. You can find them on e-bay sometimes for about $20.00. Heil Sound www.heilsound.com also sells a foot keyer that will work. I've heard that some people will add a relay inside their transceiver to key the amp. The easiest way is to use the amp with an amateur radio, most have a keying relay in them. Just make sure that there is a "soft key" circuit installed in the amp before connecting it to a modern transceiver or you will burn up the transceiver pretty quick. You can get them from www.harbachelectronics.com. Good luck and be careful if you have to go inside that amp for anything. Whatever you do, do not on turn that amplifier with the cover off! If it has the safety switch installed you will burn out the rectifier board and have a transformer meltdown. A better word of advise is "Do Not Have the Amplifier Plugged in with the Cover Off" There are lethal voltages in there that can Kill You!!. There is a wealth of information out there on that amplifier, take your time and do some web searches. Enjoy!!
73's
Triple J

 

[DuckKilla]

These type amps normally dont have an rf sensing circuit(keying circuit).You can have one installed.
Most amateur radios have a jack on the back and you connect it to the jack on the back of the amplifier and when you key the radio it keys the amp.
You can use a footswitch or toggle switch to key it via the RCA jack on the rear of the amp.This is the most cost effective method.
If your technically inclined you can also add a relay to the radio to key the amp when you key the radio.
If you install a small 12 volt relay in the radio for this purpose you will need to run a ground wire and a positive (that has at least 8 volts and is only hot when the radio is keyed) to the positive and negative inputs of the relay.
Also you need to place a diode across the positive and negative leads on the relay.
You will then need a volt ohm meter so you can find two pins on the relay that are open unkeyed and closed when keyed by checking continuity.
Once you have chosen these two points you will need to solder two wires either a quick disconnect(two wire setup) or an RCA type connector with wire thru the chassis to go to the amp.
On Galaxys and Ranger bases just use one of the RCA connectors that are already on the rear of the radio.
Disconnect the wires going to the RCA connector and tape them or cover them with heat shrink so they wont touch anything and cause problems.
Solder the two wires from your relay to the RCA jack.
Put an RCA jumper between the radio and the amp and your done.
An amateur radio will have this jack as well as alc hookup.
Hope this helps.

 

[nomadradio]

Or you can buy a "foot-switch-eliminator" kit for $30 postpaid. The relay in the kit hooks to a RCA socket on the rear panel. A Rat-Shack audio jumper hooks from the relay socket on the SB220 to the one on the rear of the radio.

The popular "black radio" base stations already have two of those on the rear, typically marked "Monitor" and "Freq Counter". That way, all you have to do is hook it up to them. A radio with no spare sockets gets the RCA socket added to the rear panel.

Don't have the instructions ready for more than a couple of base radio types, but here's the install for a 2990DX.

Installing the KeyBoard in the RCI2990DX

The foot switch works okay, so long as you step on it before you key the drive power. Hit the switch AFTER there is drive, and an arc forms across the standby side of the relay in the linear. Eventually that will wear out the contact points.

There are folks who sell a "hot-foot" adapter that senses your RF from the radio like a CB linear. This is okay for barefoot radio drive, but the SB-220 is bigger. If the relay chatters with this setup, bad things can happen. The 'cable' hookup won't do that.

The current 'wish list' of model-specific install instructions are the Galaxy Saturn/Eagle 2000, Galaxy DX2517, Cobra 2000GTL and a few others.

The first version had only one output. The current version has two, one for the driver, and one for the 'big' box.

73

 

[four6zero]

OK, so to keep it simple, I just get a foot switch from Heil or Radio Shack as long as it has the phono male end plug at the end, it should work. Have the sb220 already keyed before hitting the exiter. Now does it matter which plug it goes to, on the back of the sb220 it has 2 phono end plugs marked "antenna relay" & "alc". Which one?

Also, they recommend 100w drive to get full output. Does that mean 100w deak key or 100w of modulation? I am assuming they mean 100w rms.
If I key 100w and modulate to 150w rms, am I overdriving it? What can happen?

Thank you, All you fellow Radio hobbiest for all the info you've given.

 

[nomadradio]

The socket marked "relay" is the one you want. The one marked "ALC" isn't much use, even if your radio HAD a socket with an ALC input.

The amplifier is set up for SSB, meaning that the tubes will throw at least 200 Watts of heat (each!) WITH NO DRIVE when the high/low switch is set to "SSB" (high), so long as the foot pedal is held down. This is to keep a SSB signal clean, and is no big deal on sideband. No carrier to heat the tubes.

AM is another matter. Heathkit says to use the "CW/Tune" (low) side for AM. This is to keep the added heat from your AM carrier from getting out of hand.

If you insist on running AM on "SSB" (high) side, it would be a good idea to have the amplifier modified, to reduce the "no-drive" tube current on SSB. Other weak spots on the band switch, input circuit, grid circuit, standby bias, and parasitic chokes get beefed up as well to run AM on high side. Adding protection diodes to the two meters is a good idea for a 'hot-rod' operator. If either of those meters is damaged by a surge, you'll have to dig down deep for a replacement. Two rectifier diodes added to each meter are FAR cheaper.

With the stock "SSB" setup, the added heat from your AM carrier will be too much for the tubes by the time you've been keyed up for more than 10 seconds or so. It's a SSB amplifier design, so AM will be hard on it if you use high side without any modifications.

I recommend no more than 200 Watts carrier coming OUT of a STOCK SB-220, set to "CW/Tune". Expect 750 to 900 Watt peaks this way, depending on how large your driver is.

The driver will need to deliver between 15 and 30 Watts carrier to get 200 Watts carrier out on "CW/TUne" side.

The type and age of the tubes, as well as other factors will dictate just WHERE the drive carrier needs to be set. Don't worry about how many Watts of drive carrier, worry about how many Watts the carrier reads coming OUT of the SB-220. THAT'S what matters, not how much drive it took to keep it below 200 Watts coming out.

You may have heard of folks who "hot-rod" the SB-220 on AM, running it on the "SSB" side, swinging 2000-plus Watts. A whole list of modifications is needed to keep a "hot-rod" SB-220 from skidding off into the ditch at that drive level. A STOCK SB-220 will NOT stand up to that for very long. If you try this, you will discover the handful of "weak spots" in the design that get beefed up for full-bore AM operating.

Oh, and if you want to use it as a driver, another handful of things will need to get beefed up. Driver service is harder on the SB-220 than just feeding an antenna with it. Changing the Tune and Load controls to increase the spacing between the plates is part of that routine.

Nearly every legit "ham" linear meant for SSB will need to be turned down to its 'low' side for AM if it's stock.

And if you're running SSB, go for it. That's what it was configured to do best. Somewhere between 1500 Watt peaks and 2000 Watt peaks is the dividing line between stock and 'hot-rod' power level.

And there is no "minimum" drive level for the SB-220. Drive it with a barefoot single-final "ten-meter" radio on high side, and you'll get between ten and twelve times the drive power coming out. A low drive level will NOT hurt the thing. At all.

73

 

[four6zero]

Thank you very much Mr. Nomadradio.
Out of curiousity, where can I get that info about Full-Bore AM Use 2000+ watts?

 

[nomadradio]

Uh 460,
For starters, we can skip that "mister" stuff. One of the oldest traditions of amateur radio is that everybody is on a "first name" basis. Whether you're a king, a clown, pauper or fat cat. I suppose that idea had a lot of appeal when I was 12 years old, but it sank in very early.

As to where you'll find this info posted on the web, beats me. We developed our own 'hot-rod' routine the old-fashioned way by trial and error, with some guidance from the math. That, and paying attention to the same parts that ALWAYS got hammered as soon as a SB-220 was put onto AM.

All we have are the parts list and cryptic notes on the old (1987) word processor. One of these days I'll convert a few hundred old Wordstar files to something modern. One of these days.

I shot the pictures to write a step-by-step (sorta) web page for this, and that's where the project stalled.

Next web page on the wish-list for the SB-220 is our low-voltage relay replacement kit. Selling a few of those would pay for the time spent writing it up that way.

Problem is, the wish list is out of hand and just getting longer. The hot-rod AM-operator 'beef-up' routine is too far down the list for now. Unless I found a way for it to pay for itself.

Had the half-defrosted idea of offering the parts for the process in a kit. Would be easier than placing 3 or 4 separate parts orders for one of this, and two of that. The background effort would include getting that list worked up with supplier catalog numbers and backup suppliers. Then a good supply of all the parts on the list would be the next expense.

Once I get it to that point, I'll have so much money tied up in the idea that I'll finally get off my ass and write the web page for it.

Seems to be the only thing that gets one project to the top of the pile. On the other hand, until I have something (actually) on hand to sell, it's pointless to show it to the world on a web page. Chicken and egg problem, sorta.

I worked out a poof-proof replacement for the failure-prone zener diode, and started the web page for installing it in a SB-220. It holds the tube heat down enough to permit using the 220 on "SSB" side for AM. Figured that would get me motivated to write up the install procedure for it, but they sell too fast here, in and out the door. Before I can get nervous about the money I spent to make them, they're sold, and it's time to order another batch. The local walk-in trade still pays most of the bills. Web stuff is still a side line (stepchild). Gets treated like one.

I did post a bunch of the pictures from the step-by-step, never-written web page in a folder on one of the Yahoo groups web sites. Been long enough I don't remember which one.

(short pause)

Checked Yahoo Groups. It's in the "photos" folder named "SB220_Customized_For_AM" in the "Tube_Amps" group. Not too helpful, since all you can see if you join the group and click on them is a shrunken "semi-thumbnail". Doesn't allow access to the full resolution of the "photo" file unless you're a moderator, or the user who posted it. Go figure.

Even with 36 pictures in the folder, it's not enough detail for a Ray Doty-style "wordless workshop" (remember those?). I posted those pics in October '03, and then figured out that the rest of the project was a lot bigger than I bargained for. Got discouraged (distracted) and found a project small enough to complete.

And there's the rub. Got a handful of things like the SB-220 low-voltage relay and zener board. Each waiting until its web page gets written, to sell the first "guinea-pig" batch, and see how many "bugs" are in the install procedure.

But that stuff is still in the 'stepchild' category. Waiting for slack days in the repair business.

If experience is any guide, I'll get it done a week before the 3-500Z tube finally gets discontinued. Forever.

Know anybody who needs to replace the burned-up High-Voltage boards in his Pride DX-300 base amp? Got plenty of that one on the shelf to sell. Heck, that one's even on the web. Just click the tiny "www" button at the bottom of my post, just below the sig.

Probably shoulda skipped that one and worked up the SB-220 stuff instead. Live and learn, I guess.

73

 

[four6zero]

NoMad,
Is there a difference between the sb220 & sb221 besides the 10m band?

 

[nomadradio]

That's the biggest difference. They left out the 10-meter hookup and input coil. They also installed a low-pass filter in line with the input side of the band switch. It has to be taken out of the input circuit to convert it for 10/11 meters.

Pretty sure the 221 was sold only factory-assembled, not as a kit. The aluminum chassis is just too flimsy to permit shipping the amplifier with the transformer in place. This was no big deal with the kit version, but an "assembled" SB-221 was also shipped in three cartons. One with the tubes. Another with the HV transformer and the other one with the amplifier.

The "assembled" version still required you to bolt the HV transformer in place, but had nylon connctors for the wires. It just plugged in.

Shipping a SB-220 with the heavy HV transformer installed is a pretty risky proposition. If it gets dropped along the way, the chassis deck may separate from the rear panel, shearing along the rear flange. I have seem plenty of "crooked" HV transformers sitting on a bent chassis deck, and cracked circuit breakers, if it drops down far enough.

Used to be you could ship delicate stuff by Greyhound and be pretty safe. Those days are probably gone, by now.

73

 

[four6zero]

Hey Nomadradio,
I asked this on the other thread, and later realized I was asking on the wrong section.
Do voltage pass thru the foot switch?
How does this work?
This is all new to me and I want to understand how it all works..

 

[nomadradio]

Hi 460,
Yeah, with the foot switch open, there will be around 130 Volts DC across the switch contacts.

When the switch is closed, it passes about 10 mA of current. That's one one-hundredth (1/100) of an Amp.

Either the contact points in a relay or the contacts in a foot switch will USUALLY take this alright without damage. It's the guy with a new, computerized all solid-state radio who gets surprised trying to hook it to a SB-220.

Most of that kind of transceiver will only switch LOW voltages SAFELY on the "linear key" jack, and that 130 Volts from the SB220 will slap the tar out of a few sensitive, low-voltage chips and such. Very sad. And expensive.

Older ham radios that had an ACTUAL mechanical relay inside, connected to the "accessory" socket will key it just fine.

This is what they now refer to as a "soft-key" modification. Reduces the standby-side voltage on the linear's key jack to a low value that's safe for newer transceivers.

BTW, if the relay in that SB-220 goes bad, let me know. I'm working up a kit with a 24-Volt relay, a tiny transformer to run it, and a 'soft-key' board that keeps the switch voltage down to about 6 Volts. I'm still mired in making up a decent instruction page for putting it in.

73

 

[four6zero]

Nomad,
What do you think of the Hot-Foot Keyer?
I'll use it after the radio, before my 2 pill driver 100w/ or a one-tuber modulator- does about 50w. Do you think the Hot-Foot will work properly?
I better ask now before I try to attempt such a thing.

 

[Triple J]

I noticed Will Matney the builder of the Hot Foot Keyer is on the forum's blacklist.... I have a bunch of e-mails from him since I was in the market for something two years ago. I eventually changed my mind and went with the amateur radio. If there is a different or new builder of the Hot Foot Keyer, I apologize for my mistake and request one of the admins to delete this post.

http://forum.worldwidedx.com/viewtopic.php?t=1234

http://www.freewebs.com/skunkworks/hf.htm

 

[nomadradio]

The name "Hot Foot" is just one guy's name for a generic solution. Namely, putting the internal "keying circuit" from an external CB-type amplifier in its own box, to use with a ham-type amplifier like the SB-220. This function is normally built into amplifiers meant to work with a radio which was NOT meant to use with an amplifier. It borrows a tiny fraction of the radio's RF drive power to trigger a switch transistor, and operate the linear's changeover relay.

This method works okay for AM, but is not too swift for SSB. If you place it in line with the radio (AHEAD of the driver), this should help to make the big box key before the driver "wakes up" and starts to deliver drive power. If the SB220 relay keys 'late', after the driver has begun to deliver power, there will be an arc across the relay in the SB-220 every time you key. Not good for the life of the relay. Same hazard exists if you don't press a foot switch BEFORE keying the radio.

A smaller drawback is the potential that a "hot-foot" keyer will permit the relay to "chatter", or open and close rapidly while the driver is pumping power. A bad jumper, loose coax connector or antenna problem could cause this. The bigger the amplifier, the more risk of harm from a chattering relay.

Good design of the external "RF Sensing" keying circuit will make chattering less likely. For AM, anyway. For SSB, I still favor the 'direct key' solution hands down. For AM, the difference between the two methods is not so large when it's done right.

73