Parasitic Suppresser

Discussion in 'Amateur Radio Amplifiers' started by KA5ROW, Jun 13, 2012.

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  1. KA5ROW

    KA5ROW Ham Member QRZ Page

    parasitic suppresser ????:

    Would the parasitic suppresser from a Kenwood TL-922 work in a Heathkit SB-220? If not why not. It would seem to me that any amplifier that used that tube. The parasitic would be interchangeable one to the other.

    Question 2 : when I rebuilt my amplifier TL-922A, I replaced the cracked carbon resistors in the parasitic with new film type resistors. What does the resistor do? You have a resistor wound like a choke, resistance is nil in the choke, ohms law parallel resistance I less that the least resistance of the two, in this case the wire wound choke.
    I have also noticed some parasitic's have some sort of nickel wire vs copper vs silver. Is this important. Why not in the case of the SB-220 use copper wound around a film resistor
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

  3. W1QJ

    W1QJ Ham Member QRZ Page

    Parasitic suppression needs to be looked at as a "system". It's NOT "one size fits all". To answer your question without beating around the bush, yes, it is possible that the TL-922 suppressor will work in the SB-220. You have to try it and see. That is the BEST answer to that question. The idea of the suppressor is to block energy of the parasitic so it does not get amplfied. The short circuit of the coil is not really seen at the parasitic frequency so the ohms law thing applying to DC does not hold up because it is impedance and not resistance in the real sense. So the parasitic sees the resistor and not the short circuit of the wire coil. At DC the short circuit prevails. One California ham sells Nicr suppressors but his theroy on why they work is always under question and was somewhat dissproved here a while back. Again, that is not to say they don't work. Since I have experience with most 3-500 amps, it seems that the suppressors that come with the amps work well and there is no need to change them. Older amps that have carbon type resistors are prone to the resistor changing value due to age and heat dissipation. On some bands the resistor does get hot. Carbon resistors don't like alot of heat. Metal film and similar non inductive resistors made today will tolerate heat much better without changing it's value.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think in most amps, the parasitic suppressor resistors always get hot, if you really use the amplifier, because they're usually an inch or less away from the anode caps! Conducted heat alone is almost enough to unsolder them.

    Higher temperature carbon film "flameproof" resistors which have been on the market at least 20 years are better. Using silver solder to install them helps prevent thermal "uninstallations.":eek:
     
  5. W1QJ

    W1QJ Ham Member QRZ Page

    In that respect (conducted heat) that is very true Steve. Good point.
     
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    Is It Voodoo Time Yet?

    I'm waiting for a certain ham to check in with his sales pitch for his magical nichrome low-Q suppressors. My 2 x 3-500Z amplifier has survived nearly 40 years with two sets of tubes, using the OEM supressors, on all bands from 80 thru 10m. :D
     
  7. N3JBH

    N3JBH Ham Member QRZ Page

    Maybe after G0HZU busted him, he want underground and started a email campaign. ;)
     
  8. G0HZU

    G0HZU QRZ Member

    I wouldn't exactly say I busted him, I just didn't agree that NiCr wire made the significant difference that he claimed.


    Also, to be fair to Rich, some of his suppressor designs may well be very effective but I would argue that his choice to use NiCr wire isn't the reason they are effective. He has clearly got a lot of experience in making up various topologies of suppressor and he has quite a few happy customers so in this respect he is doing OK :)
     
  9. G0HZU

    G0HZU QRZ Member

    The other thing is that maybe it's time to revisit the analysis of these amplifiers and why suppressors are often needed.

    Also, look at the other system issues in a typical amplifier that contribute to other potential instability modes.


    I've read the analysis on the W8JI web page and as is usual on Tom's website there's a lot of good stuff on this subject.

    There's also several statements that aren't quite right IMO and some that are misleading.

    But overall the analysis method isn't that of an engineer, it's the analysis of a radio ham. Maybe that's because it's aimed at radio hams but to me it could be dealt with better with basic system analysis to model the mode of instability and also how the suppressor can be used to improve stability.

    The best way would be via a youtube video IMO.
     
  10. KM1H

    KM1H Ham Member QRZ Page

    Typical JI way of doing things which is why I never recommend it to someone just learning. The only way anything gets corrected is when he is publicly hammered enough to quietly make a change as if it was always that way.

    Ive worked with the 3-400/3-500 since they were available starting in the early 60's and Ive yet to find any suppressors that arent interchangable as long as they physically fit. Dont use one for a 572B on a 3-500. Its really an easy tube to stabilize as long as the suppressor value stays close to tolerance. Heat and lots of RF is a killer to carbon composition resistors and the recent Ohmite OY series ceramic resistors have worked out well for me for the past year or so.

    I think Rich is a nice and well meaning guy who got dropped on his head a few times too many:eek: all that voodoo nichrome does is mask the problem with an elaborate brute force bethod best described as Voodoo as Ive used since the 90's with Rich going back to the old AMPS forum where JI thought he was the appointed emperor. Even then he got slapped around by REAL engineers but was protected by the site owner until he went SK trying to launch a Mustang airborn into a pond.

    Carl
     
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