sb200 no/low output on 10 meters

Discussion in 'Amateur Radio Amplifiers' started by WX7G, Sep 29, 2019.

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  1. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi Glen:

    FB regarding the SB-200.

    I built the LV keying interface into my SB-200 and added a zener diode to the ALC, per the Heathkit appnote. I had done similar mods to my old HW-101 to allow it to be driven by an AEA AMT-1 (remember those?) and later a PK-232, for RTTY and AMTOR. I used a couple of bipolar HV switching transistors, with good results.

    My TS-440SAT drives the SB-200 just fine and can easily overdrive it on 20M-80M if I'm not careful.

    Brian - K6BRN
  2. WA9SVD

    WA9SVD Ham Member QRZ Page

    I had a 1972 VW "Bug," and I I still see them on the road today, after over 47 years. Will YOUR " brand spankin' new, 2019" vehicle model still be on the road in 2066? In 2056? In 2046? Even in 2026?:confused::rolleyes:
    SM6CJB likes this.
  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    Sorry, buddy. I've had just a little experience maintaining "bugs", including engine rebuilds and (North) east coast body rot. Most of the bugs I grew up with (and later, the "Things" are) iron rich fertilizer by now. Thank VW the darn things had separate (removable) castings for the cylinders, because they never lasted more than 40K miles without a rebuild. Unless you didn't mind an oil smoke fog bank trailing behind the car. Of course, I never had a new one, so maybe out of the dealership they lasted a little longer? At 35 HP, the split window bug I spent a lot of time with was mostly maxed out all the time. And who needs a fuel guage? When the engine sputtered, just kick over the reserve tank rod on the floor. No turn signals... it had these nice little wooden "flags" that popped out of the... well... C-Pillars I guess. Might have been a bright color once, but all the paint was gone on the flags on this one. Oh... and I think I still have a piston with a slightly melted crown from a trip (almost) over the mountains.

    Pure quality, those bugs. NOT. Simple, yes. Built to last - not so much - unless you put plenty of time into them. And a LOT of spare parts. Don't believe Woody Allen in "Sleeper". Leave one in a cave for 100 years and all that'll be left is the glass parts. In pieces.

    So... maintain, restore and baby ANY car (or piece of junk) and it'll last a century. No problem. Might not be completely original any more, but it'll still be there. Sort of.

    And modern cars are WAY, WAY more reliable and safe.

    Brian - K6BRN
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Agreed, I had a '63 bug which I loved but I worked on constantly. I always likened them to lawn mowers, you could keep them running forever but you'd better be prepared to work on them fairly often.

    But that's also where your SB-200 analogy breaks down. You don't need to constantly maintain an SB-200, sure it's older and lacks bells and whistles of newer amps but an SB-200 in good shape just works day in and day out without needing regular maintenance. Yup, you don't get instant QSY without retuning nor fancy LED bargraph metering but as an amp it does its job nicely and unlike the old car analogy it isn't overly prone to breaking down nor put you at risk to use one.
  5. K6BRN

    K6BRN XML Subscriber QRZ Page


    Not my experience. The current SB-200 I have has had the following maintenence (and NEEDED it):

    1. New (old stock) Cetron tubes.
    2. Replace bad caps in voltage doubler board, the board itself (phenolic material beginning to flake off)
    3. Replace ragged power supply cord.
    4. Replace electrolytic caps in RF underdeck
    5. Retune input network and replace some mica caps to bring it into correct range for tuning.
    6. Replace numerous carbon cop resistors due to drif & disintegration
    7. Partially disassemble and repair meter as it became intermittant.

    And that's just "maintenence", not the upgrades I had to add to make it safe and workable with modern rigs.

    I've been using it off and on since 2016 and just two weeks ago, during a normal QSO, one of the two 572B tubes went "POP" and looks like its toast. Time for a new (really new) set of tubes and to inspect the inside for damage.

    This amp is 50 years old and is VERY similar to a VW bug that's passed through MANY hands with varying degrees of skills. Its also "Simpler than a lawnmower". But not really very reliable anymore.

    My Quadra and KPA-500 just work, with zero problems. The KPA-500, in particular, is very simple inside. I built it from a kit, and all parts are readily available. The're are a LOT of them out in the field and they are likely to be around a LONG time.

    So I think the analogy holds to a reasonable degree: My half-century old VW bug (SB-200), originally built for low cost, that has probably been "rebuilt" a dozen time by numerous owners (and is unreliable), vs. a much newer (but still years old) solid-state, no-tune KPA-500 (modern car wit airbags and A/C).

    I use the KPA-500 or Quadra as my "daily drivers" and take out the SB-200 for a spin when I'm feeling nostalgic, just the way you'd drive your restored Model T to a car meet. And it "broke down and melted a piston", again, recently.

    It's fine with me that you love and use an SB-200 on a daily basis - I used to. But that time is past. For serious (hobby) business, I use what works, every time.

    Best Regards,

    Brian - - K6BRN
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    That's a one time refurb, not regular maintenance as compared to adjusting the lifters in a VW engine every few months.

    Actually I use an AL-80b on a day to day basis but used my SB-200 for about eight years as my shack amp. Yes, I did much of the refurb work you mentioned like replacing the caps when I first got it but the amp never once let me down which I can't say for my '63 bug. ;)
  7. K9STH

    K9STH Ham Member QRZ Page


    Any older unit needs to have the electrolytic capacitors replaced as as a precaution. With the SB-200 / SB-201 the HV meter resistors need to be checked and replaced if necessary. Total parts cost, less than $30.00.

    A low voltage keying interface can be built for around $10.00.

    Unless the amplifier has been abused, it will be fine. Frankly, any amplifier, be it current production or "boat anchor", can be abused and then all bets are off.

    When I obtained my present SB-200 (I sold off my original SB-200 back in the mid 1970s), the first thing that I did was to replace all of the electrolytic capacitors. The tubes are the original Cetron 572B and those are still putting out full power. I got a spare pair of Centron 572B with the amplifier. No need to even think of installing them.

    Most of my "exciters" have a relay that can easily handle the keying voltage of the SB-200. However, I do have a couple of units that require an interface. Therefore, I did construct such and have the ability to switch among all of my exciters if I want to use any of them with the SB-200.

    I do NOT try to get more than around 600-watts out of the SB-200. The station, on the other end of the QSO, can't tell the difference between 600-watts, 700-watts, or even 800-watts. But, the tubes will certainly know the difference and you are just increasing the "bottom line" of your electric company running the higher power.

    If I need higher power, I just use my Collins 75S-3A / 32S-3 into my Henry / Tempo 2001. That amplifier can make 1400-watts without any difficulty.

    The SB-200 is better built than the Ameritron AL-811 / AL-811H and can certainly take a LOT more abuse than those very popular amplifiers.

    Glen, K9STH
  8. K6BRN

    K6BRN XML Subscriber QRZ Page

    David (KT7RF):

    You. Adjusted. The lifters? Hmmmm. With all the engine clatter, I didn't think it made a difference. :)


    I don't really care about parts cost too much. It's about spare time and where I'm going to spend it. Cost a LOT more than $30 to refurb the SB-200. About $300 to $325. And that was when I had a LOT more spare time.

    New tubes, caps, doubler board, band switch, carbon comp resistors, some wiring, soft key, ALC limiter, soft start (since I was there)... the list was pretty long. And it took a while. Point is, there is still a LOT of other old stuff in the chassis (fan, transformer, meter, cardboard tuning cores, NOS Cetrons...). And as I said SNAP! Something went last week - likely one of the Cetrons. I do have a spare pair, but there is a LOT of mielage on them. And I have to see if anything else was damaged.

    So... I'm going to roll this fix into the "Maintenence" category. Just like when the meter died last year (I actually repaired it - loose internal wiring).

    Nah! This SB-200 needs a lot of attention. It always does. Its old. It runs OK for a while, then... poof! SOMETHING happens. I'm so short of time personal right now I may just give it to one of the clubs I belong to.

    FB on that. And LESS on 15M and 10M for sure. 400- 500W SSB is a safe bet on those bands. I often use an outboard cooling fan I place on top of the chassis as well. Helps for long QSOs with some compression. I NEVER run digital modes or CW with it.

    Yep. It sure is. The SB-200 is built around a much better tube than the 811.

    Well - back to FT8 now, with my Quadra (leather seats, automatic transmission, A/C, regular (500W) and "turbo" mode (1KW) etc.) There's SOME life on 40M tonight, at least. Then I'll band hop. Easy to do with this amp attached to an FTDX-3000 - it just follows along.

    Brian - K6BRN
  9. K9STH

    K9STH Ham Member QRZ Page


    It sounds like the particular SB-200 that you have was a "basket case" when obtained! Although I don't specialize in working on amplifiers, over the years I have worked on a fair number of SB-200 / SB-201 examples. Most examples can be updated in around 2-hours, including adding an interface relay, with a parts cost of $50.00 or less.

    Of course, those are examples that have not been abused. If someone has an example that, often, was used by a "CBer" or "freebander", then all bets are off!

    Yes, around 500-watts on 15-meters and 450-watts on 10-meters are about average with the SB-200. When I do operate on those bands, I usually use the Henry / Tempo 2001 and get almost 3-times the output. The SB-200 doesn't cover 160-meters and neither do my other 2-amplifiers. As such, a while back I built a home-brew 160-meter amplifier using a pair of the Russian GI-7bT tubes that, with a puny plate power transformer, puts out around 850-watts (with a better plate transformer it would, probably make well over 1000-watts output). When I operate on 160-meters (primarily during contests), the amplifier definitely helps.

    Glen, K9STH
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I agree the KPA-500 is pretty wonderful.

    I never owned a Quadra, but have heard (mostly on the air) numerous reports of them failing for various reasons. Seems the power supply is the leading cause.

    Re the SB-200, it sure was popular and there are still a lot of them on the air. The Yaesu FL-2100 series seems to be a "let's make it prettier" copy of the SB-200, but I like the SB-200 better. Yaesu sold a boatload of FL-2100 amps also.

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