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RE: [CDV700CLUB] Low HV on CDV-700

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  • Tom Herman
    Hi Carl, First off, what are you using to measure the HV? Remember that this is a high impedance supply, and a standard VOM, even a DMM with 11 MegOhms
    Message 1 of 4 , May 1, 2010
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      Hi Carl,
       
        First off, what are you using to measure the HV? Remember that this is a high impedance supply, and a standard VOM, even a DMM with 11 MegOhms impedance will load the PS and falsely show you low voltage.
        You should use a HV probe (with a 990 or 1000 MegOhm resistor) in series with your meter to measure HV. Of course, you multiply by 100 what you read to get the actual voltage.
        If you actually are getting clicks, then the PS is probably OK, as that signifies you're at least at the plateau voltage of the tube (probably 800+ volts).
        Yes, use the 2N404 or 404A... Almost any PNP Germanium will work.
        IIRC, the metering tranisistors aren't as demanding, and low HFE transistors work well. I think for the oscillator, you need an HFE or somewhere between 75 and 125 for it to work properly.
        The real biggie is the proprietary transformer on the Vic 6B: It has B+ on it all the time it's on, and has a propensity to short out. It's Unobtanium, except for members here that have a few shashed away.
        Good Luck!
       
      -Tom
       

      To: CDV700CLUB@yahoogroups.com
      From: drakel4b1@...
      Date: Fri, 30 Apr 2010 15:22:35 -0700
      Subject: [CDV700CLUB] Low HV on CDV-700

       
      I purchased an 'as is' CDV-700 6B made by Victoreen. I have the correct schematic but the HV is low (about 200V). I set the current at 33mA adjusting R5A. Still about 200V. T2 is not making much noise. Scope held close to CR3 show pulses of low amplitude. Removed 6993 GM tube but HV is still low. Disconnected regulator - had no effect. I'm suspecting Q2 but the germainium is house numbered and have not found any cross on internet although one forum suggested a 2N404 as a sub. I have not found any shorts in HV section. Any idea  what a good sub for Q2 and what other area have I missed? Thanks




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    • Carl
      Tom,        Thanks for the info but the HV PS is sporadic. It did seem to work but now very little. I removed Q2 and replaced it with a 2N1705, curve
      Message 2 of 4 , May 1, 2010
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        Tom,
         
             Thanks for the info but the HV PS is sporadic. It did seem to work but now very little. I removed Q2 and replaced it with a 2N1705, curve traced the original to at least see if it compairs but I found that the original seems good. The other problem I found is the unit was modified by placing a 0.025 uF cap across #4 and #6 of T2. Looks like someone took a lead from 'Anton" and the schematic of thier model 6. Just to see what would happen I removed the cap and what little oscillation I had was lowered by more than 80%. I'm aware of the loading trying to measure the HV but there is no background clicks (obviously because of low HV). The other mod I found when making sure all the connections are good ( they sure did not know how to solder in the early sixties - I've been a ham for 45 years! ) is a small switching diode connected between E & B of Q1 with the cathode connected to the base. Any ideas? I don't want to drill out the mounting rivet on T2  as yet but I had considered the possibility of T2 being shorted. TNX
         
        Carl
         
         

        --- On Sat, 5/1/10, Tom Herman <n1bec@...> wrote:

        From: Tom Herman <n1bec@...>
        Subject: RE: [CDV700CLUB] Low HV on CDV-700
        To: "CDV700CLUB" <cdv700club@yahoogroups.com>
        Date: Saturday, May 1, 2010, 10:43 AM

         
        Hi Carl,
         
          First off, what are you using to measure the HV? Remember that this is a high impedance supply, and a standard VOM, even a DMM with 11 MegOhms impedance will load the PS and falsely show you low voltage.
          You should use a HV probe (with a 990 or 1000 MegOhm resistor) in series with your meter to measure HV. Of course, you multiply by 100 what you read to get the actual voltage.
          If you actually are getting clicks, then the PS is probably OK, as that signifies you're at least at the plateau voltage of the tube (probably 800+ volts).
          Yes, use the 2N404 or 404A... Almost any PNP Germanium will work.
          IIRC, the metering tranisistors aren't as demanding, and low HFE transistors work well. I think for the oscillator, you need an HFE or somewhere between 75 and 125 for it to work properly.
          The real biggie is the proprietary transformer on the Vic 6B: It has B+ on it all the time it's on, and has a propensity to short out. It's Unobtanium, except for members here that have a few shashed away.
          Good Luck!
         
        -Tom
         

        To: CDV700CLUB@yahoogro ups.com
        From: drakel4b1@yahoo. com
        Date: Fri, 30 Apr 2010 15:22:35 -0700
        Subject: [CDV700CLUB] Low HV on CDV-700

         
        I purchased an 'as is' CDV-700 6B made by Victoreen. I have the correct schematic but the HV is low (about 200V). I set the current at 33mA adjusting R5A. Still about 200V. T2 is not making much noise. Scope held close to CR3 show pulses of low amplitude. Removed 6993 GM tube but HV is still low. Disconnected regulator - had no effect. I'm suspecting Q2 but the germainium is house numbered and have not found any cross on internet although one forum suggested a 2N404 as a sub. I have not found any shorts in HV section. Any idea  what a good sub for Q2 and what other area have I missed? Thanks




        The New Busy is not the too busy. Combine all your e-mail accounts with Hotmail. Get busy.

      • Joe Mew
        Carl, i ve had a number of CDV700s of all mfg randomly die on me due to humidity, i ve had really good luck baking them at low heat for 5 or 6 hours then
        Message 3 of 4 , May 2, 2010
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          Carl, i've had a number of CDV700s of all mfg randomly "die" on me due to humidity, i've had really good luck baking them at low heat for 5 or 6 hours then potting them with generic potting compunds rated for high voltage applications. if you can't get yours working i have a lionel 6b board that works fine, not sure if it would bolt into your unit thou. message me off group if you need that board.

          --
          Joe Mew <skelite@...>
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