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SB-200 Damaged plate on "TUNE" capacitor

Discussion in 'Amateur Radio Amplifiers' started by KJ4AQU, Apr 1, 2012.

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    The SB-220 amp tunes really sweet on 80 and 40 meters. While turning the load and tune you can see a a nice swing on the meter and you can identify the peak output easily without missing it. On 20 its a little more critical but still not bad. On 15 and 10 meters you had better be sober, steady, and don't blink an eye or you will miss that sharp peak in output. After the peak it drops off quickly. Vernier tuning would have been nice for those bands. Surprisingly the "el cheapo" (as everyone calls them) Ameritron amps do have vernier tuning to their credit. As far as numbers, I am in awe of how many SB-220 amps were bought. They are for sale everyday in multiples on just about every sales venue dedicated to ham radio. There are probably 4 to 6 each week on EBAY, every week without fail. Several on other venues as well. Anyone know how many were sold? And to think they were kits in the late 60's to late 70's and you had to build them! Seems like old time hams knew how to solder. I built 2 new ones myself way back when.
     
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    I tune up in just a few seconds, and I don't consider myself more careful than most. In fact, I've tried to tune up with the bandswitch in the wrong position. Thankfully, when that happens, the input network prevents any IG from flowing, with the resultant spitzensparken.

    Thankfully, I keep my bandswitch nuts tight. :rolleyes: But then, I don't wrench it against the stops and I doubt very many others do. You were just "lucky" to find a few bandswitches that weren't tightened enough.

    The electrical design had some easily-corrected issues but Heath's mechanical design was mostly OK, including the method of holding the outer cover in place. They used it for ALL the SB-series cabinets. The sheetmetal screws used to hold the inner shield compartments in place was OK as long as they didn't get removed/installed many times. My SB-220 suffered from a few enlarged holes. Now, it has PEM nuts, which were super easy to retrofit with the shield side panels in place. :)

    Mine tunes easy enough on all bands - I see no need for a vernier drive (or other ways to slow the PA tuning). In fact, between 20-15-10m, CTUNE is very close to correct for each band. It takes only a second or two to touch it up. No vernier tuning needed... just don't adjust it (here it comes) ham-handed. ;)

    In many ways, they're still a very good deal, if you can find one that hasn't been all hacked-up and/or priced out of the market.
     
  3. W1BR

    W1BR Ham Member QRZ Page

    Ameritron uses vernier drives on their amps, and I am sure that Martin J. would have gone to direct
    drive to save a few pennies, if there was any advantage to doing so. I certainly see a big difference
    in being able to tune on 15 and 10 meters on the SB-220 with the venier drive.

    Pete
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, the reduction drives help a lot on 10-12-15m, that's where they matter most.

    PEMs are really cheap, I'm amazed they didn't use them. They were available in the 60s and all you need is an auger press to install them. Other methods might work, but I always used a press.

    Yes, installing covers via the screwed-in feet is fine with lightweight gear, but the SB-220 is around 50 lbs and I thought that was very silly for something so heavy, which you have to kind of sit on its face to slide the cover off. Better ideas that cost nothing extra are abundant. Even the Johnson Ranger, which is another piece that's designed stupidly mechanically, used long machine screws front to rear so you could slide the cover off the back and not have to sit it on its face. (Although I never liked their approach, either.)

    The SB-220's "tuned input" switch is very hard to access once it's assembled and there's no easy way to adjust the slug tuned coils once it's assembled. Shame on them. I can think of a dozen ways to do that better, all of which add no cost.

    That's why I think the "mechanical design" was really lacking.

    But it worked. I bought one and built it and it never failed.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I should mention: Take a look at the Henry amps from the same era.

    Input tuning readily accessible. They used chains and sprockets for tuning, which although seemingly complex, really aren't and they almost never fail. In the "big" amps, there isn't any wafer bandswitch except for the input circuit; the output tank is switched by a camshaft driving plungers which can handle probably 20kV at 5A if they needed to. Brilliant mechanical design, and they didn't cost too much more than the Heath SB-220 at the time.

    Heath needed a better mechanical engineer.
     
  6. W1BR

    W1BR Ham Member QRZ Page

    The SB-220 was a good design, despite some of the shortcomings.

    I switched over to the WDS7 TU6A input board when I added the 160 meter coverage.
    I never cared for the arrangement for the input matching network. I probably dropped
    more $$$ in "upgrades" than the amp was worth, but compared to what a new amp costs
    it was worth the investment.

    Pete
     
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    I agree that even on 10-12-15m, reduction drives are not necessary unless the user has little dexterity.

    PEMs are cheap but labor to install them isn't. I installed mine without any special tools unless you consider Vice-Grip™ pliers a specialty tool. For a one-off installation, the little bit of extra time was no big deal.

    The feet on the SB-220 are a compressed part, not a stressed part. Therefore, little mechanical strength is needed. In nearly 40 years, I've never had an issue with it, nor heard of anyone having an issue with it. Until now.

    I'll agree that access to the input circuit is very bad. Fortunately, I've never had a reason to adjust mine.

    IMO Henry stuff was overall not a lot better or worse... just different.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think my dexterity is fine, and might have been better 40 years ago when I built my SB-220, and always hated the way it "quick tuned" on the higher bands, especially 10m. Just no reason for that.

    In a production environment, we install about 1500 PEMs per hour using a simple pneumatic Auger press. We have two of them, with two operators, so they can crank out about 3000 an hour. If each is paid $20/hour, this means the cost to install them is about 1.3 cents each. This isn't rocket science.:p We crank out about 1000 chassis a day with a relatively small shop, and they all have a lot of PEMs. We do have automated feeders which may not have been available in 1970 (I really don't know).

    My only "issue" is that it's a silly design. Would have been equally easy to use half-covers to access top or bottom independently (since bottom access is very rarely required) and make the cover a clam-shell, for about zero extra cost. Then the top could be removed without doing anything with the feet or having to lay the amp over to do it. Simple stuff.

    I think most people haven't. However if you like 17m or 12m, those users often like to peak the input circuit for a better match on those bands (possibly sacrificing the match on 15m and 10m) and Heath made it really difficult to do, for no reason I can see.

    I disagree there. Henry stuff is WAY more robust...power transformer's twice as large and runs ice cold at full load; rectifier circuit is tuned-choke input and regulated like crazy...typical drop from key up to key down is maybe 100V. Plate bandswitching is cam and plunger activated, they absolutely never fail no matter what you do. Tubes are cooled by blower and chimneys, as recommended by Eimac. Keying circuit is low voltage (12Vdc) and not HV as used by Heath, for no reason I could ever understand.

    Henry also usually used higher B+ to provide more gain and output. The last Henry amp I bought, the 3K Premier, used 3800V on the anode and when they said "3K" they weren't kidding. That was in 1985.
     
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    My mistake. You're right. I'm wrong. End.
     
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    WIK:

    You have to remember that Heath equipment was generally aimed at a lower socioeconomic strata than the Henry amplifier. There were many more Heath SB-200 and SB-220 amplifiers sold than Henry even dreamed of. For the money, the SB-200 and SB-220 gave performance unheard of until those amplifiers came on the market.

    Glen, K9STH
     
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