Ohmite Parastatic Suppressor P-300

Discussion in 'Off-Topic' started by oidium45, Jun 19, 2010.

  1. oidium45

    Thread Starter Active Member

    Apr 24, 2010
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    Hello everyone!

    This is definitely off topic but does anyone know what the value of a NOS 1939 Ohmite Parastatic Suppressor P-300 would be these days? According to the paperwork in the box they sold for $1.58 in 1939.

    I cannot seem to find any information about this component online.


    By value i mean usefulness and going rate.

    And no, I am not trying to sell these. I am just looking for info...
     
    Last edited: Jun 19, 2010
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Classical capitalist theory would suggest that something is worth what someone is willing to pay for it. Someone with a period radio might be an interested party.

    Despite the exciting title, the critter appears to be a wirewound power resistor. It's hard to say if the wire is even insulated, although the "enameled" part of the Ohmite part description indicates it should be. What is the resistance?
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    ONE MILLION DOLLARS! ;)

    or not.

    As beenthere said, it is worth whatever someone is willing to pay for them.

    As for ACTUAL value(worth), a more modern resistor with better ratings(Higher wattege, less leakage or noise, smaller, and more modern metals with better heat dissipation are readily available.

    Now-a-days, high wattage resistors are incorporated in extruded anodized aluminum cases that helps with heat dissipation.

    However, if someone is rebuilding a car, plane, radio, whatever, from the 30s or 40s, using these for the exact "LOOK" of the original would be worth much more than someone who is just looking for a 300 ohm resistor (Or whatever it ends up being)
     
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  4. hgmjr

    Moderator

    Jan 28, 2005
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    I suspect that the components would be more valuable to someone as a collectable rather than for use in an actual circuit.

    hgmjr
     
  5. Ghar

    Active Member

    Mar 8, 2010
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    With 'parasitic suppressor' in the title and the odd core in the middle this could be a type of lossy inductor like a modern ferrite. Just fishing but who knows...

    I bet I'm just biased by the 'ite' in 'Ohmite' :)
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    "Lossy inductor" is another definition of any wirewound resistor. That core is a layer of some ceramic material over a steel rod. Ohmite wirewounds aren't really that exotic.

    It would be interesting to know what prompted the fancy title.
     
  7. Ghar

    Active Member

    Mar 8, 2010
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    It's sort of an ambiguous phrase, since a ferrite is an inductor with core loss (high frequency) but low DC loss. A wirewound resistor is high loss at DC with an inductive component.
    That huge wire gauge and short length makes it look fairly low resistance but it does depend on the material.
    I've obviously never played with older stuff like this so like I said I'm just fishing.
     
  8. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    We used modern version of these things on rf PA amps inline on the grid leads to stop VHF parasitic oscillation in tubes.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    Perhaps then we could use "low value inductor with a really poor Q". But it is that inductive nature of a wirewound resistor that makes them very unsuited for high frequency applications. The higher the resistance, the more turns of resistance wire.

    There may be some reason for this kind to have the resistance element exposed. The ones I am familiar with were completely enclosed in a porcelain body with a nice shiny glaze. As printed circuits came into wider use, there was a line of mounts available that poked into the hollow core and could be attached to the PCB.

    Ohmite still makes a wide line of power resistors. The ones from Dale were spiffier, as they had the core shoved into a finned aluminum body with mounting feet. We had several big ones for load resistors - 1 ohm each and 250 watts dissipation.
     
  10. nsaspook

    AAC Fanatic!

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    I think because it was used at RF and high voltage, most of the coatings of the time were pretty poor dielectrics. I've seen a few of these smoked when a tube ran-away from parasites so they can get pretty hot from voltage in the VHF range.
     
  11. oidium45

    Thread Starter Active Member

    Apr 24, 2010
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    Yes I think that they could possibly be of interest to a vintage HV collector. They look pretty cool from a vintage standpoint.

    I tried to measure the resistance of them but it was vary low...
    Two of my meters read 0, and another read 0.6 ohms.
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    The library of Congress has all sorts of operating equipment and might need one in their spare parts collection.
     
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  13. VoodooMojo

    Active Member

    Nov 28, 2009
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    here is an excellent response from PROUD MARY to the same request from another posting:



    Registered Member #2838
    Joined: Fri Apr 30 2010, 02:55PM
    Location: Rosamond, CA
    Posts: 75
    I have four (4) Ohmite Parastatic Suppressors P-300 manufactured in 1939 new old stock. They are in the original packaging with paperwork. I have included a scan of the paperwork and a photograph of the resistors below.
    I am unsure what they are worth. Here is my aim...

    1) If anyone would like to fill me in on any good info (value, good uses, specs, etc...) that would be great!
    2) Anyone interested in a possible trade???
    3) Anyone interested in buying please send me an offer.

    I am not sure that they will be vary useful in my tc design but they sure look cool!

    “I do not think there is any thrill that can go through the human heart like that felt by the inventor as he sees some creation of the brain unfolding to success... Such emotions make a man forget food, sleep, friends, love, everything.” (Nikola Tesla)




    Proud Mary Sat Jun 19 2010, 05:40AM
    Registered Member #543
    Joined: Tue Feb 20 2007, 10:26AM
    Location: UK
    Posts: 2030
    Anti-parasitic suppressors were often fitted into the control grid and anode circuits of thermionic valve RF power amplifiers, especially where two or more valves were wired in parallel.

    The idea was that the inductor would present a very high impedance at VHF and UHF, but present a negligible choking effect on the desired HF and DC. VHF and UHF fluctations, which might otherwise have triggered unwanted oscillation, could not pass the inductor, and so were driven into the resistor, to be dissipated as heat.

    Anti-parasitic suppressors were often home made by winding a small coil on a carbon resistor.

    It was often said that the anti-parasitic chokes fitted in grid and anode circuits should be of different sizes, to reduce the possibility of Tuned-Anode-Tuned-Grid type parasitic oscillation, but your chokes do not seem to take this possibility into account.

    I have not seen many tests of spectral purity on VTTCs, and wouldn't be surprised if some designs suffered from all sorts of power-sapping parasitic oscillation and were radiating all over the place. You might have a use for them yet.
    Look at the light! It's full of stars!Back to top
     
  14. oidium45

    Thread Starter Active Member

    Apr 24, 2010
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    "here is an excellent response from PROUD MARY to the same request from another posting:"

    You have figured out how to use google! That is wonderful!

    Anyway, thank you all for your feedback.

    I was hoping to find a useful way to use these in a project because I like their vintage look. But it sounds like their only usefulness will be within a high voltage project in which I have been informed is a "no-no" as far as topics of discussion on this site.

    I believe that I am just going to trade them for something more useful for my current projects.
     
  15. retched

    AAC Fanatic!

    Dec 5, 2009
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    Not necessarily high voltage, but high or very high frequency.

    They would look better in an electro-art piece as part of the eye-candy. Put them on a pcb and light them with a color changing RGB LED and it will LOOK cool. As for usefulness, as VoodooMojos time combing the archives has uncovered, except for valves/tubes using UHF or VHF, are just heaters.
     
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  16. oidium45

    Thread Starter Active Member

    Apr 24, 2010
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    Beenthere,
    In case you are still curious...
     
  17. retched

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    1929..wow.
     
  18. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Care to venture a guess on what in 1929 was considered UHF?

    I had those suppressors in the control grid circuit of the push-pull parallel Power Amplifiers designed in 1950s.

    Yes it suppresses parasitic oscillations....even when the primary frequency was in the VLF band.
     
  19. oidium45

    Thread Starter Active Member

    Apr 24, 2010
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    Not that it makes much difference but the date on the paperwork is actually 1939.
     
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