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SB 200 with 200 watts out ???

Discussion in '"Boat Anchor" & Classic Equipment' started by ka7gtp, Jul 1, 2008.

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  1. ka7gtp

    ka7gtp Guest

    I have recently installed the Harbach PW200 power supply and soft start in my SB200 and I'm showing only 200 watts out. The reason for the change was the power out was gradually lowering from 500 watts down to 200 watts out, I replaced the 572 tubes in the amp. thinking that the tubes were going "soft", so I ordered a new set from RF Parts. I already ordered the pw200 and received them,and when the new tubes arrived, I did the "up-grade" and tube replacement at the same time. I took my time and made sure that the solder connections were correct and solid. I let the tubes idle for about twenty hours " no power out " just the input power from the house current. I am useing the amp on 120 volts,as there is no 220 into the shack. Also the meter is now only working on HV and rel pwr ,it was working in all positions before the install.
    My question is : where did I go wrong, and is there anyone that can help me correct the problem ?
  2. WB3BEL

    WB3BEL Ham Member QRZ Page

    Sounds like it is only running on one tube.

    Be very careful working on this as the high voltage is unforgiving...

    See if the filaments are lit in both tubes.

    Check the plate suppressors. They are the resistors have a coil of wire surrounding them. They often burn out if the amp is tuned improperly on the higher bands.

    In order to tell if the amp is working on just one tube, take one out and see if it goes to almost no power. If not that one then put it back and take out the other one and see if it goes to almost no power out. If so then you know where to look more closely.

    For a theory of operation look here:

    Harry WB3BEL
  3. K7GQ

    K7GQ Subscriber QRZ Page

    I wonder what band you're checking the power out on? I had an experience where a relatively new set of (Chinese) tubes put out low power (200-250 watts) on any band above 40 meters, but full power out on 40 and 80 meters.
  4. W9GB

    W9GB Ham Member QRZ Page

    Art -

    The inability to have the meter work in all positions, indicates to me that you may have a wiring mistake.

    First, you stated that you are operating at 120 VAC, and not 240 VAC.
    Did you order RES-121? which is required with the PW-200 when the amplfier is operated from 120 VAC.

    The Harbach PW-200 module is a NEW printed circuit board that combines the functionality of the PM-200 replacement power supply module and

    the SS-201 soft-start module for the Heathkit SB-200/SB-201.

    The Harbach PW-200 kit ONLY includes power resistors for 220/240 VAC mains operation. IF the amp is operated on 110/120 VAC mains, the resistors MUST be changed to 10-ohm 10-watt. These may be ordered on the Harbach website (part number: RES-121).

    Second, Harbach does not yet have the PW-200 instructions on their web site. IF you were given the seperate instructions, then a wiring error may have been made -- when you tried to transpose those instructions to the new PC board.

    Lastly, IF this is a new Heathkit SB-200 for you (purchased at hamfest or eBay) -- it is POSSIBLE that it was originally wired incorrectly; has been tampered with by former orwners; OR the wire colors used are different and do not match the Harbach instrructions!

    The original Heathkit Assembly Manual is invaluable and should be near this amplifier for reference purposes.
    SB-200 Manual at BAMA Mirror:

    Robert Norgards, KL7FM's notes on upgrading Heathkit SB-200

    Other SB-200 resources:


    BTW, Jeff Weinberg (Harbach) is normally available weekday evenings:

    Harbach Electronics, LLC
    468 County Road 620
    Polk, OH 44866-9711
    Phone: (419) 945-2359
    Fax (419) 945-2359
    Last edited: Jul 1, 2008
  5. ka7gtp

    ka7gtp Guest

    sb200" low power"

    hi guy's , thanks for the tips.
    BEC, I didn't check to see if it was feeding one tube or both, I'll check that this week-end, thanks again.
    I only use tha amp on 40 & 75 meters,so only check it on those bands into a dummy load {Heathkit } and driving it with a TS140S at this time. I have had the amp four about eight years,and it was working F.B. before the gradual decrease in out-put power.
    Thanksfor the input,
    I ordered the upgrades back in 2005 when Jeff was still doing the soldering and selling the upgrades already assembled,and at that time the PW200 was not availible,so I'll order them in a week or so,until then I thought someone may have had the same problem and had a "quick-fix".
    Thanks for the input. Art
  6. W9GB

    W9GB Ham Member QRZ Page

    OK, so you actually have the PM-200 replacement power supply module, that I referenced earlier.

    1. Go through the steps I suggested as well as other responders.
    In addition, how clean are the contacts is that SB-200 meter switch?

    2. Jeff is the best "expert" to figure out what is not proerly connected (or if there was a mistake in his original board).

  7. KM5FL

    KM5FL Ham Member QRZ Page

    You probably haven't done anything "wrong" except that none of the repairs and upgrades you've done repaired the original problem... Those resistors that bypass the step start relays will not "support" the current required to run the amp, so the reduced power problem does not lie with the step start resistors.. During the initial milliseconds of turn on, AC current flows thru them but as soon as the relays close, the load is removed from those resistors. If, for some reason, the relays don't close, the resistors will overheat and the smoke will be let out... The resistors will open and the amp will shut down. Believe me, you will know if that has happened..

    Have you checked the power on all the bands?? It's possible the power reduction is cause by problems within the input matching circuits.. Your transceiver may be "seeing" a high SWR condition and cutting back on the power to the amp.

  8. W6ZR

    W6ZR Ham Member QRZ Page

    sound like you are only useing one half of the input voltage. when you put
    in your Setp start,you put in backwards?the relay only stays in for 1 sec.
    then it short out the 10 ohm R and now you get the full power.if you get the relay
    wired wrong? it will work backwards.the R is in the line all the time and your voltage is less then half,?check to be sure that when you turne on the SB200
    the voltage is les then half for just 1 sec.them you should be getting full voltage on you plate meter. good luck 73 W6ZR Ray
  9. W4AFB

    W4AFB Guest

    I just had a similar problem with my 200. I turned out to be a bad connection at the top of the tube where the resistor goes. From being takin on and off over the year the wire broke. I soldered in a new wire the leg of the resistor and works fine now.Also you may have caps going bad in the power supply.
  10. KC8VWM

    KC8VWM Ham Member QRZ Page

    I agree, sometimes the original builder wires them wrong (reversing wire colors etc. ) but yet they are actually wired in a manner they actually function correctly. (a common problem)

    So it's possible when you replaced the PS board you "think" you were wiring them back in correctly, (according to the correct "assumed" wire color) but in fact you're not doing it in the same way the orginal builder wired the circuit.

    Check the switch wiring against the schematic while using a multitester to ensure the contacts didn't go sour. For example, you have to be careful when removing and replacing the cover on the chassis because the meter function switch has one particular pin located on the very bottom that can sometimes get "snagged" on the cover when sliding it on or off the chassis.

    It's possible when you replaced the PS board, you may have caused a wire break to occur on the switch that is barely visible. (I did) Sometimes this is the result of "old or weak solder" joints.

    Another reason the amplifier may not be producing full power is because one of the two 33 ohm grid resistors located on the pins of V1 and V2 may have opened but if the meter switch is not working correctly I would fix that first.
    Last edited: Oct 6, 2010
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