Wow, 600 bucks. Makes me wonder if that's a "Needs 30 years of maintenance done" price, or a "Did the 30 years' maintenance already" price? Seems to me the ones with new power-supply components and tubes tend to sell for nearly twice that much.
Uhhh, did they say whether or not it works? Or, how many years it's been since anybody last SAW it work?
Since it says "SB-220" and not "221", it still has 10 meters on the band switch. That's what you'll use for 27 MHz. Also means it was made before 1979 or so. Oldest it COULD be is 37 years, more or less.
It's a SSB amplifier. If you plan to use it for AM, leave it on the "low" (CW/TUNE) side. The "SSB" (high) side can be used on AM only after some modifications are made to reduce the tube heat to a safe value. The continuous heat from an AM carrier will hurt it on "SSB" side without mods.
It has no way to "sense" the transmit signal from your radio. It has a "relay" socket in the rear, that gets patched to a socket on a ham-type radio. A relay inside that kind of radio closes when you key the mike, activating the amplifier from the mike switch, rather than from the radio's RF output.
The RatShack foot switch, with a plug adapter will work, but you have to keep the sequence right. Key the foot switch BEFORE the radio, and release it only AFTER you have released the key on the radio. This way, the relay in the SB-220 won't have arcs form across the contact points. If your drive power is applied when the amplifier's relay changes position, your drive RF can wear out the contacts prematurely.
Adding an 'external key' relay inside a radio that doesn't have one is the solution I recommend. The amplifier keys as soon as you press the switch on the radio's mike. If you run SSB a lot, this is a LOT smoother than having it key and unkey every time you take a breath.
We have a kit for this, but haven't worked up installation guides for more than a handful of radios yet.
Here's one for the Galaxy Saturn Turbo. www.nomadradio.com/OldNomadWebPages/KBTurbo/index.htm
Modified SB-220 amplifiers routinely get driven to over 2000 Watts PEP output. A stock SB-220 shouldn't get more than 150 to 180 Watts PEP drive. The input circuit won't take much more than that, if it's stock.
Age is an issue with a linear that can't be any newer than 28 years old. If the original high-voltage filter capacitors are in it, they will fail soon. Even if they check okay after a long shelf visit, the stress of operating (even on standby) will usually cause them to 'remember' how old they are, and break down before long.
Cleaning out the band switch contacts, the relay contacts, the tubes' glass surfaces, the tube socket's contacts (and tubes' pins) can save you grief down the line. The years take their toll here, too. So do the miles. For a large amplifier like this one DIRT IS DEATH!
If the fan blade doesn't spin freely, then THIS AMPLIFIER IS DOOMED, DOOMED I SAY!. It needs the airflow. Really. Friction in the fan motor will reduce the speed of the fan, and the flow of air with it.
The meters are famous for burning out when a tube fails, or someone leaves the ground ring loose on a coax jumper. Placing a parallel back-to-back pair of rectifier diodes across each meter can save you genuine grief. Nobody has those meters any more. Nobody. Except the occasional Ebay seller. Average price there is 70 bucks or more. Much cheaper to protect the meters you have.
It's a fairly reliable "pickup truck" of a linear, so long as maintenance doesn't get neglected. I don't think I'd drive a 1979 pickup truck very far before I checked the differential's gear-oil level. Much better than having it lock up on the freeway.
Oh, and yeah. Both knobs get set for MAX MODULATED SWING. A peak-reading meter is helpful, but not absolutely necessary.
Taking it apart is SUICIDAL !, so don't tell anybody I suggested it. Wouldn't want to get sued by your survivors. But a look around for scorch marks, cracked or discolored parts is wise, before applying power. Ground screws are famous for coming loose, or being left loose by home builders. Seeing that all of them are tight is on our "check list" before applying power to one of these.
JUST DON'T RUN IT WITH THE COVER OFF ! ! It has a spring-loaded "crowbar" switch that is held open by a insulator bolted under the inside shield cover. It's meant to discharge the HV filters when that cover is removed. LEAVE IT OFF WHILE POWER IS APPLIED, AND YOU'LL BLOW UP THE HIGH-VOLTAGE SUPPLY and (maybe) the grid meter, grid-choke coils, rectifiers, meter resistors, errr. You get the idea.
Have fun. Hope you survive the experience. 3000 Volts is just, plain nasty stuff. Deadly, to boot.
And the manual can be downloaded from
bama.sbc.edu/heath.htm
Scroll down the page a long way, you'll find the SB-220 there.
73
Uhhh, did they say whether or not it works? Or, how many years it's been since anybody last SAW it work?
Since it says "SB-220" and not "221", it still has 10 meters on the band switch. That's what you'll use for 27 MHz. Also means it was made before 1979 or so. Oldest it COULD be is 37 years, more or less.
It's a SSB amplifier. If you plan to use it for AM, leave it on the "low" (CW/TUNE) side. The "SSB" (high) side can be used on AM only after some modifications are made to reduce the tube heat to a safe value. The continuous heat from an AM carrier will hurt it on "SSB" side without mods.
It has no way to "sense" the transmit signal from your radio. It has a "relay" socket in the rear, that gets patched to a socket on a ham-type radio. A relay inside that kind of radio closes when you key the mike, activating the amplifier from the mike switch, rather than from the radio's RF output.
The RatShack foot switch, with a plug adapter will work, but you have to keep the sequence right. Key the foot switch BEFORE the radio, and release it only AFTER you have released the key on the radio. This way, the relay in the SB-220 won't have arcs form across the contact points. If your drive power is applied when the amplifier's relay changes position, your drive RF can wear out the contacts prematurely.
Adding an 'external key' relay inside a radio that doesn't have one is the solution I recommend. The amplifier keys as soon as you press the switch on the radio's mike. If you run SSB a lot, this is a LOT smoother than having it key and unkey every time you take a breath.
We have a kit for this, but haven't worked up installation guides for more than a handful of radios yet.
Here's one for the Galaxy Saturn Turbo. www.nomadradio.com/OldNomadWebPages/KBTurbo/index.htm
Modified SB-220 amplifiers routinely get driven to over 2000 Watts PEP output. A stock SB-220 shouldn't get more than 150 to 180 Watts PEP drive. The input circuit won't take much more than that, if it's stock.
Age is an issue with a linear that can't be any newer than 28 years old. If the original high-voltage filter capacitors are in it, they will fail soon. Even if they check okay after a long shelf visit, the stress of operating (even on standby) will usually cause them to 'remember' how old they are, and break down before long.
Cleaning out the band switch contacts, the relay contacts, the tubes' glass surfaces, the tube socket's contacts (and tubes' pins) can save you grief down the line. The years take their toll here, too. So do the miles. For a large amplifier like this one DIRT IS DEATH!
If the fan blade doesn't spin freely, then THIS AMPLIFIER IS DOOMED, DOOMED I SAY!. It needs the airflow. Really. Friction in the fan motor will reduce the speed of the fan, and the flow of air with it.
The meters are famous for burning out when a tube fails, or someone leaves the ground ring loose on a coax jumper. Placing a parallel back-to-back pair of rectifier diodes across each meter can save you genuine grief. Nobody has those meters any more. Nobody. Except the occasional Ebay seller. Average price there is 70 bucks or more. Much cheaper to protect the meters you have.
It's a fairly reliable "pickup truck" of a linear, so long as maintenance doesn't get neglected. I don't think I'd drive a 1979 pickup truck very far before I checked the differential's gear-oil level. Much better than having it lock up on the freeway.
Oh, and yeah. Both knobs get set for MAX MODULATED SWING. A peak-reading meter is helpful, but not absolutely necessary.
Taking it apart is SUICIDAL !, so don't tell anybody I suggested it. Wouldn't want to get sued by your survivors. But a look around for scorch marks, cracked or discolored parts is wise, before applying power. Ground screws are famous for coming loose, or being left loose by home builders. Seeing that all of them are tight is on our "check list" before applying power to one of these.
JUST DON'T RUN IT WITH THE COVER OFF ! ! It has a spring-loaded "crowbar" switch that is held open by a insulator bolted under the inside shield cover. It's meant to discharge the HV filters when that cover is removed. LEAVE IT OFF WHILE POWER IS APPLIED, AND YOU'LL BLOW UP THE HIGH-VOLTAGE SUPPLY and (maybe) the grid meter, grid-choke coils, rectifiers, meter resistors, errr. You get the idea.
Have fun. Hope you survive the experience. 3000 Volts is just, plain nasty stuff. Deadly, to boot.
And the manual can be downloaded from
bama.sbc.edu/heath.htm
Scroll down the page a long way, you'll find the SB-220 there.
73
