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Mallory 50V 2500uf large can capacitor question

  1. Mar 20, 2016 #1
    Hi guys,
    I am trying to replace two 1960's Hunts 50V 2500uf large can aluminum capacitor that are in a 1964 transistor Vox T.60 bass amp. The capacitor is about 4 inches long and 1 and 3/8 inches in dia.
    I see on ebay a Mallory 2500uF 50V Large Can Electrolytic Capacitor CGS252U050R4C3PH for sale of the same size and near the same color.
    I can not seem to find a data sheet on the old Hunts capacitor or the new Mallory.

    In today's world I ASSUME there is no need for such a large form factor electrolytic capacitor and I could use a smaller cap and "hide" it inside the old Hunts can.

    Am I missing something??

    Cheers,

    Billy

    BTW: All of this is part of trying to rebuild a 1964 Vox T.60 bass amp. This was the first transistor amp every built by Vox and was a serious failure. It is unstable and eats output transistors for breakfast...lol

    upload_2016-3-20_15-13-32.png
    This is a comment someone on another forum made. "This T60 amplifier circuit must have a very high THD because it use a driver transformer, bad bias of the output transistors (probably class B) and has no feedback"

    The idea is to return this amp to as close to original as I can and not to address the design flaws. Well....I guess, at least at this point.
     
  2. jcsd
  3. Mar 20, 2016 #2
    Here is a short video of the amp in question.

     
  4. Mar 20, 2016 #3

    davenn

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    That's what I would do if you are wanting to do a good lookalike restoration :smile:


    Dave
     
  5. Mar 20, 2016 #4
    Hi Dave,
    I actually think the "hide" the new capacitor is the best solution. While I am pretty sure the Mallory capacitor will work ok it is not the exact same color as the old Hunts and would be quite noticeable as not being original.

    I am not so sure about what to do with the Mullard OC44 black glass germanium transistors. I have only seen one ad for sale for OC44 transistors which are in England. That guy says he has 12 in total. $40 for all of them, with free shipping, which is not the end of the world even if they don't work. I have not found any others for sale anywhere. If I can not find original OC44 germanium that are still good I then have a re-design issue to deal with using modern silicone transistors and no way to "hide" a new silicone transistor inside a black glass old OC44 even if I could get it apart with breaking it....well...I guess that is a true statement. Perhaps a very tiny transistor that would work exist.

    This will be a fun project in any event!!

    Cheers,

    Billy

    The OC44 black glass transistors are only 5mm in dia.
     
  6. Mar 20, 2016 #5

    davenn

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    If you are going to change these to silicon, don't forget you will have to do some other circuit rearranging as biasing and other parameters will be different

    I wouldn't change the old OC types unless absolutely necessary


    D
     
    Last edited: Mar 20, 2016
  7. Mar 20, 2016 #6

    CWatters

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  8. Mar 20, 2016 #7
    Thanks for the ebay links. The first two I was aware of but not the third. I was able to find a data sheet in German for the OC44 black glass ones so perhaps I can find a data sheet for the metal can ones to see if they match.

    I am with Dave on not making any changes that are not absolutely necessary.

    I have read some post that describe some possible changes to silicone. I think the changes would be difficult at best for me understand and make.

    This amp worked when it left the factory, perhaps not very well and not for long. I think I want to get it back to original or as close as that can be done.
    The Serial number is 0786. I sort of assume that at least 786 were made...well...if the numbers started at zero. The point being that a bunch of them worked with this design at least for a while.

    Vox as I understand the history, stopped production at some point and went back to tube design on the next model. They said they felt like they did not understand transistor design well enough at that moment in time to continue making transistor amps.

    I do not feel like I understand transistor amps well enough at this moment in time to to re-design there amp...lol

    Cheers,

    Billy
     
  9. Mar 20, 2016 #8

    davenn

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    As an aside
    We (many of us) used to use the OC series transistors as photo detector transistors by scraping an area of that black paint off

    ohhh, them were the days ... you are bring up all sorts of old memories using those devices :wink:


    Dave
     
  10. Mar 21, 2016 #9

    davenn

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    hahahaha that made me laugh :DD

    silicone = fake boobs
    silicon = semiconductor material
     
  11. Mar 21, 2016 #10
    Hi Dave,

    lol...perhaps fake boobs is just what this amp needs...lol

    Brain damage is a funny thing...lol...it comes from living in France for too long and sticking an "e" on the end of everything...lol

    Cheers,

    Billy
     
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