sb200 no/low output on 10 meters

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

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    New cars crunch really bad in accidents these days. Technology didn't keep them for folding up and costing mega-bucks to fix in a body shop. The idea was less weight and fit more into a smaller package. The Henry 2K band switch is a brute no argument there. The new breed of ham likes smaller compact radios with lots of bells and whistles and that goes for amps too. The Henry band switch is a huge component and the amp it's in is huge too. Don't bang up a new car and don't arc a band switch in a new amp with minimal headroom. Those Henry's are big monster amps.
  2. K6BRN

    K6BRN XML Subscriber QRZ Page

    Or... simply get a new, more modern amp with no tubes, no bandswitch problems and "airbags", like the KPA-500. Not too many people with 50-year old cars as their daily driver.

    Brian - K6BRN
    K6LPM likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    With the Heath amps, I've had to replace bandswitch wafers before; and while the owner usually will not admit it, I'm pretty sure by the way they failed the switch was turned while transmitting.:p That ain't good.

    At least in the Ameritrons there was an attempt to prevent this by making the bandswitch at a different level, and using a very different knob, from the PLATE and LOAD caps. Of course, anything's possible, but at least placing the switch on a different plane, and using a completely different kind of knob on it, makes it less likely to be rotated while transmitting as it won't be confused for one of the tuning controls.
    K7TRF likes this.
  4. W2VW

    W2VW XML Subscriber QRZ Page

    Newer hams reading some of this stuff might make the decision to buy something costing ten times as much for the same power because it has a warrantee.

    Most hamplifiers are very simple and all of them will break if they are abused.
  5. K9STH

    K9STH Ham Member QRZ Page


    My SB-200 still has its original U.S. made Cetron 572B tubes and they are still putting out 600-watts up through 20-meters dropping to just under 500-watts on 10-meters. This measured on the wattmeter in my Collins 312B-4. I do have a spare pair of U.S. made Cetron 572B tubes, but, so far, they are not needed. Of course, I don't "push" the amplifier to get more power output. The operator, on the other end, is not going to tell the difference between 600-watts, 700-watts, or even an absurd 800-watts out of the SB-200. However, the tubes are sure going to notice the difference as well as adding to the profits of my electric company.

    I did replace the electrolytic capacitors a while back as well as upgrading the high voltage rectifiers to use 1N5408 diodes.

    My Henry / Tempo still has its original 8874 tubes from 1972 and they are also putting out full power. A few years ago, just as a contest was starting, the amplifier lost one of its electrolytic capacitors. I replaced all of the capacitors. Again, I don't try to get an absurd amount of power out of the amplifier.

    Glen, K9STH
  6. K6BRN

    K6BRN XML Subscriber QRZ Page

    Glen (K9STH):

    Glad you are enjoying your SB-200. I have NOS Cetrons in mine. But the amp has been through a significant rebuild. The transformer and metering is a little ragged, though, and I have my doubts about the NOS Cetrons. I have to decide just how long I'm going to keep this old friend alive.

    Right now, My Quadra at QTH#1 and KPA-500 at QTH#2 are the "daily drivers".

    David (W2VW):

    Not just for the warranty - but because it's 10x more capable: Junker 50 year old SB-200 (about $350) vs. new KPA-500 (about $1800 kit) - cost difference is about 5x. Capability difference - light years: reliable, warranty, no-tune, can run 500W average power for a LOOOONNNG time and not blink, uses WAY less power, smaller, lighter, CAT controlled, fault protected.

    It's the difference between a banged up VW bug and and a new 2019 sedan. Which would you rather drive on a daily basis?

    Brian - K6BRN
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    There has been a lot of virtual ink spilled on this subject. I'll spill some more but keep it short. Let's hone in on your problem and gather info to solve it.

    Do you have any electronics repair experience? What radio are you running into this amp? The suggestions you will get depend on the answers to these questions.

    Start by reading the manual to familiarize yourself with the sections of the amp and precautions for working on it. In particular, pay attention to how the front panel meter behaves looking at HV when you shut the amp off. It should start out at 2300 volts or so and slowly drop to zero over a 10-20 second time frame. If it doesn't do this, tell us before doing anything inside.

    If the power supply discharges properly and you're OK with tools and opening it up, make sure the power cord is unplugged. Remove the screws on the side of the outer cabinet to flip the top up and post a few pictures of the guts so we can see what shape this amp is in. Pictures are important. We can look at them and see if there's been any bad juju going on with the device.

    Let's start there.
    KA9JLM likes this.
  8. W2VW

    W2VW XML Subscriber QRZ Page

    I'd rather have CWA's SB-200 and save my money for something new that actually works better than something from 1969. Maybe an Anan.

    But I'm one of those weirdos who runs AM.

    Not only that but my amplifier is almost 10 years older than CWA's and I'm using a tube with a 1963 datecode.

    If I wanted a solid state HF amplifier I'd re-purpose some of the 360 MRF-151gs I have here.

    The only thing really crummy about an SB-200 is lack of resolution on the plate and load markings.
  9. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi David (W2VW):

    Mmmm. Nothing wrong with AM in my book. If you enjoy it, work it!

    Having lived through the late '50's till now, it's pretty clear that just about anything modern in technology, including cars, radios, TVs, telephones, etc. works WAY better than in 1969. It's fun to collect and play with the old stuff, but better? No. Not by a long shot.

    It's fun to play with antiques. I have a Santa Claus Christmas tree incandescent bulb from 1929, and it still works. Been in my family for years. So I understand your amazement that your 56 year old tube still works. A good friend of mine collects antique tubes. And I collect clocks that are 100+ years old (drives my XYL nuts). But neither of us relies on them.

    You're going to need a little more than a few RF transistors to do that. And why did you acquire so many MRF-151gs, anyway? Seems a little like you bought a "mystery box" at a hamfest and... surprise! A bunch of transistors inside. Good for you.

    But, since you've never had a solid state amp, maybe you should mosey over to an Elmer's station - an Elmer that has one, and see how much difference it makes. It's a LOT! Why deny yourself the experience, unless it's a budget issue. But then, fantastic deals to come by now and then - and if you are not looking, you miss them. Live a little.

    The SB-200 was a magnificent excercise in design-for-cost engineering, back in the day. But that was 50 years ago and both the design and the materials are more than showing their age in a major way. Almost any other choice in modern amps is better. But, again, if you like antiques and repair projects (I do), then bravo! This hobby has many side to it, and it's all about enjoyment.

    Best Regards,

    Brian - K6BRN
  10. W2VW

    W2VW XML Subscriber QRZ Page

    Dear Bryan,

    Please refer to

    Part 97.1 Basis and purpose:

    (d) Expansion of the existing reservoir within the amateur radio service of trained operators, technicians, and electronics experts.

    You may notice that FCC leaves out any mention of amateur radio's existence being for the collection of shiny new gizmos.

    While its true that on the air discussions of things technical has largely been replaced by consumer type discussions, I still hold hope for the future.

    Apologies to those who are interested in SB-200s with low output on 10. I would be happy to continue this tangent in another venue.

    Notice for newer hams considering an older amplifier. The mass confusion generated by people gifted with the ability to type quickly can be properly filtered with a little experience.

    I'm now looking for an SB-200 beater to retrofit with tubes that don't generate miles of speculation on the internet. Email good here.

    Have the very fine business best of days,

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