Heathkit SB-200 Parasitic Suppression?

Discussion in 'General Technical Questions and Answers' started by N7SGM, Apr 6, 2010.

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  1. N7SGM

    N7SGM Ham Member

    Hello,

    I have recently read some articles about the VHF parasitic suppression commonly found in this amp as well as others. I have an SB-200 that is working OK but wonder if I should change the parasitic suppression components. There appears to be a few different schools of thought on this as well.

    One of which is described as simply using a 56 ohm, 2 watt, carbon resistor with a piece of teflon insulated 12awg wire about 13cm long fashioned in a loop and soldered to each side of the resistor for each of the two suppressors.

    My amp has the original 2 resistors with the nichrome wire wrapped around them and soldered.

    Another is to use 2 each resistors with looped nichrome wire wrap formed off the resistor and soldered to it - 2 each resistors per tube side.

    Soooo, which type of suppressor circuit would work the best or does it really matter?

    Thanks very much!

    de
    Bob
     
  2. W5RB

    W5RB Guest

    Soooo.......it works fine , and you want to know the best way to fix it ?
    :confused:
     
  3. N7SGM

    N7SGM Ham Member

    Gotcha, I'm not actually trying to fix it, I'm thinking that replacing these components may actually improve it somewhat. Considering the age of the amp, I am somewhat concerned that the resistors could be bad or at least have changed in value that could affect the output in a negative way. You are right to point that out - why fix something if it ain't broke? I do understand your point and thank you much.
     
  4. AI3V

    AI3V Ham Member

    Well the SB200 is a new, untested design...:D

    Rege
     
  5. N8YX

    N8YX Ham Member

    If you're experiencing symptoms of parasitic oscillation with your amp, by all means look at the suppressors. If not...you aren't going to gain a whole lot by markedly changing the circuit. The components therein are either good or they aren't.
     
  6. W5RB

    W5RB Guest

    I couldn't resist the obvious line . If you're planning to do some refurb work , it makes sense to consider the possible mods while you're in the process . This is sure not my area of expertise , ( if I have one ) , but the link below may have some useful info , from a guy that knows a thing or two about amps .

    http://www.w8ji.com/vhf_stability.htm
    :)
     
  7. K9STH

    K9STH Ham Member

    There is an old saying, especially in the southern states: "If it ain't broke, don't try to fix it!"

    My SB-200 has the original configuration and it works fine! The only thing that I did, when I "acquired it", was to replace the electrolytic capacitors and the diodes in the power supply. I recently obtained this particular SB-200 to finish the re-creation of my primary station from 1967 to 1972.

    Glen, K9STH
     
  8. N7SGM

    N7SGM Ham Member

    SB-200 Amplifier

    Thanks for the replies! I bought this amp last summer from a club stating it was in good operating condx. That was found to be true and I was happy with how well it worked. I did however decide to refurb some of its components such as caps, resistors, diodes, etc. that are well described by hams who authored mods found on the internet. I also incorporated such mods as the Harbach Soft Start and Soft Key. I have not as yet done anything to the power supply pcb or its components but I may decide to also replace the ps with the improved Harbach PS pcb/components. I think by giving this amp a little tlc can't hurt it any. If my question about the suppressor circuits seems dumb then by all means, ignor it and forgive me for sounding stupid. I'd rather ask then guess. Thanks to all who reply!
     
  9. W8JI

    W8JI Ham Member

    There is a whole lot of nonsense passed around about parasitic suppressors. It has almost become one west coast ham's sole purpose in life to say all the manufacturers from Alpha through Collins through Yaesu are in some giant conspiracy to use bad suppressors. He of course has the only cure, and if you send him money he will supply the only cure. :)

    Very few problems relate to parasistic suppressors. The only time there is a problem is when something breaks, like a resistor goes off value. Changing the entire design of something that works for 40 years, just because a carbon resistor subjected to constant very high temperatures while operating goes off value, is not a good idea. Replace any bad parts.

    The LAST thing I would do to an SB200 is change to a hairpin suppressor.

    When you are all done with all those nice mods and fancy updates to the SB200, you will have an SB200 that lasts and works just about like the original unit. If thousands of them worked fine and lived 40 or 45 years without the mods, don't expect to see much of a change.
     
  10. KC8VWM

    KC8VWM Ham Member

    [​IMG]

    Yup looks like the original one's are still ticking.... :)

    In terms of performing "mods" some make sense and some clearly don't.

    For example, the idea of adding 2 diodes across the meter terminals to protect the meter. Not sure where to buy a replacement meter for the SB200 these days so I figure .75 cents worth of parts might be a worthwhile investment.

    Another common sense mod is perhaps changing out the RCA jack to an S0-239 connector on the rear.

    Other than that, it's pretty hard to improve a proven design. Just need to clean the dust off them every once in a while.
     
  11. N7SGM

    N7SGM Ham Member

    Charles,

    I agree wholeheartedly with your comments. The RCA jack was changed on mine by the previous owner and that is a good mod. I also added the diodes to the meter because it made perfect sense as well. I don't really know a lot about HF amplifiers but many of the SB-200 mod articles I read did make sense, at the very least, to change out some of the caps and resistors that may be bad. These parts are easy to come by, inexpensive, and have given me some piece of mind. It's a good old amp and I just want to take care of it so it works OK. Suppression circuits are interesting to me and they seem to vary so much from author to author. The Harbach mods are well designed and appear to be very trustworthy as well. It's too bad we don't have Heathkit around anymore; I believe they were a great group of folks with an awesome history. Thanks for the reply Charles.

    de
    Bob
     
  12. W0BTU

    W0BTU Ham Member

    There you go. Well said, Charles. That picture is worth more than the proverbial thousand words.
    My parasitic suppressors look just like that. :)

    Having said that, I have seen 572Bs that obviously have more inductance between the graphite plate and the cap. Whether those tubes require different suppressors, I can't say.
     
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