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  • Helmholtz
    replied
    I think model YJC with the ground wire and (probably) voltage reduction would be the best choice. Will reduce power, though.
    Ground wire shorts the existing cathode resistor.
    Last edited by Helmholtz; 12-07-2019, 09:32 PM.

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  • Dave H
    replied
    Originally posted by Helmholtz View Post
    Do you have any idea which of the many Yellow Jackets converters this refers to? I understand that some of them reduce plate and screen voltage while others don't.
    From the descriptions of their web site I'd think it was a YJS

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  • Chuck H
    replied
    Good find. It seems that there are several models though. The site is rather ambiguous about the actual circuitry in each model.

    It reads to me that the one they recommend for the Vibro Champ is just a pin converter. That's not a very good idea IMO. Running an el84 at 400+Vp - Vg2 with no screen resistor and a 470R cathode resistance?!?!

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  • Helmholtz
    replied
    Originally posted by Dave H View Post
    I don't know how accurate this is. It's all I could find.
    Looks like both the plate and screen voltage are reduced by 100V

    [ATTACH=CONFIG]56280[/ATTACH]
    Do you have any idea which of the many Yellow Jackets converters this refers to? I understand that some of them reduce plate and screen voltage while others don't.

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  • Dave H
    replied
    Originally posted by Chuck H View Post
    I'd want to know more about what's inside that converter socket so I could equate the changes to real world circuit analysis before putting my stamp on using them.
    I don't know how accurate this is. It's all I could find.
    Looks like both the plate and screen voltage are reduced by 100V

    Click image for larger version

Name:	Yellow Jacket 100.Jpg
Views:	1
Size:	90.5 KB
ID:	856268

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  • shortcircuit
    replied
    After visiting the Yellow Jacket homepage , they make a yellow Jacket recommended for the Vibro Champ , it's not the one I have . Apologies for not going there first.
    https://www.yellowjacketstc.com/ampl...ecommendations posted before seeing post #18,as stated before "one of those days" Please don't throw me in the storm drain
    Last edited by shortcircuit; 12-06-2019, 10:25 PM.

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  • Helmholtz
    replied
    Originally posted by Chuck H View Post
    Right. And since guys are using these things in their Marshall heads I think there also must be a DC blocking cap for the grid in there as well.
    Yes, it's descibed here: https://www.yellowjacketstc.com/detailed-information
    Many different versions.

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  • Chuck H
    replied
    Originally posted by Helmholtz View Post
    Good observation. I also think that the black lead is used to short-circuit any existing cathode resistor and use the internal resistor for biasing instead. This would allow for better center biasing.
    Right. And since guys are using these things in their Marshall heads I think there also must be a DC blocking cap for the grid in there as well.

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  • Helmholtz
    replied
    Notice that there's a black lead on the Yellow Jacket base. I'll bet this is intended to be grounded/earthed to the chassis.
    Good observation. I also think that the black lead is used to short-circuit any existing cathode resistor and use the internal resistor for biasing instead. This would allow for better center biasing.

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  • shortcircuit
    replied
    Originally posted by Helmholtz View Post
    ??? Why not VC?



    I mentioned this aspect as the Yellow Jacket leaflet says "converts from class AB to class A operation", which does not hold for the VC.



    This makes the tube run very cold, significantly reducing clean output power. An EL84 wants something like 200R for optimum class A center biasing.
    Sorry Hemholtz , VB was stupidity on my part, typing not thinking, one of those days.

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  • Helmholtz
    replied
    Increasing the cathode bias resistor would reduce current and RAISE voltage.
    Yes it will raise plate voltage. But the tube only cares about/sees plate voltage minus cathode voltage, so...

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  • Chuck H
    replied
    Please see the edit in my post above

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  • shortcircuit
    replied
    Originally posted by Chuck H View Post
    Actually...

    It doesn't work like that. Increasing the cathode bias resistor would reduce current and RAISE voltage. Whatever your memory of how it went down I promise that you did not decrease plate voltage by putting in the higher value cathode resistor.
    Thank you, and I stand corrected . Went back and looked at my original post.. (did play with cath resistor , it took a 825ohm to get a 31.5 drop , 400v across pins 3 & 8 .38mA to get a 14v dissipation , and it did raise pin 5 to 8 from 26.62vdc to 31.50vdc) it was to lower dissipation, does that make a little more sense
    Last edited by shortcircuit; 12-06-2019, 09:10 PM.

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  • Helmholtz
    replied
    VB is Vibro Champ
    ??? Why not VC?

    it says converts from AB to A
    I mentioned this aspect as the Yellow Jacket leaflet says "converts from class AB to class A operation", which does not hold for the VC.

    I raised the cathode resistor(so now it's 825ohm) to lower my VDC from 402vdc to 386vdc
    This makes the tube run very cold, significantly reducing clean output power. An EL84 wants something like 200R for optimum class A center biasing.

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  • Chuck H
    replied
    Originally posted by shortcircuit View Post
    VB is Vibro Champ, biased down, is I raised the cathode resistor(so now it's 825ohm) to lower my VDC from 402vdc to 386vdc , sorry for the confusion.
    Actually...

    It doesn't work like that. Increasing the cathode bias resistor would reduce current and RAISE voltage. Whatever your memory of how it went down I promise that you did not decrease plate voltage by putting in the higher value cathode resistor. You should reexamine what's going on with regard to this.

    Originally posted by shortcircuit View Post
    And your post #7 is what I was wondering, it says converts from AB to A , just did a total re cap ,I don't want any thing to go poof. Thanks all for your input !!
    If I'm interpreting the literature properly I have a good guess at how the Yellow Jacket manages this. But it's only a good guess.

    Notice that there's a black lead on the Yellow Jacket base. I'll bet this is intended to be grounded/earthed to the chassis. The Yellow Jacket lit says that it converts any amp to class A "self bias". From this I interpret that the base has a capacitor that blocks DC from the grid and eliminates the cathode connection from the amp, substituting the bases own cathode resistance. Which must be an arbitrarily chosen value that is "close enough" though not idealized for most amps. I can't imagine another way they could be doing this.

    In which case it should work in a Vibro Champ with under 400Vp. But as I said above, I'd prefer to know what's in the Yellow Jacket base before endorsing it.
    Last edited by Chuck H; 12-06-2019, 08:48 PM.

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