[Amps] [AMPS] Drake L-4 negative grid current reading on meter

[Steve Scoggins]

You can try the following for power resistors:

Surplus Sales
http://www.surplussales.com/

(RWF) RW29-5K
http://www.surplussales.com/Resistors/WireWound/WW27k-799k.html

Allied Electronics
http://www.alliedelec.com/
  ----- Original Message ----- 
  From: Kevin G. Wagner 
  To: amps at contesting.com ; Steve Scoggins 
  Sent: Wednesday, November 21, 2007 1:57 PM
  Subject: Re: [Amps] [AMPS] Drake L-4 negative grid current reading on meter


  Thanks to Steve, Mike, Vic, and Lou,


     I've checked the tubes. I also purchased NEW tubes as stated in my post. Steve the R11 resistor might be my problem. Who ever owned this amp before replaced this with a 15k pot. Not sure about the wattage.  Mike I will be checking these resistors. It's been a little challenging getting the R11 resistor and the R8 resistor. It seems they don't make these type of resistor that much anymore.


  73,
  Kevin
  w2fa


  On Nov 21, 2007, at 2:08 PM, Steve Scoggins wrote:


    Hello Kevin


    A common failure in 3-500Z tubes is a filament to grid short which may be intermittent.
    This type of failure may be detected by the incidence of negative grid current (usually some plate current) during standby. Observing the safety procedures in your manual. Remove the tubes then use a VOM to check the tubes for grid to filament shorts.


    Good tubes will have infinite resistance from each of the grid pins to the filament pins.
    You can tap the tube lightly while doing the check for intermittent shorts.
    The tube check procedure described above is from the Drake L-7 manual in section 5-8.


    Also, check the 120V bias resistor labeled R11.
    This is the 5K 7Watt power resistor located on the bottom of the PS.


    The 120Vdc is switched in via Pin 5 of the RF Deck connector
    when not transmitting in order to reduce the idle currents in the 3-500Z.
    Pin 6 is the negative return for the plate HV and the 120Vdc bias.


    Steve


    ----- Original Message ----- From: "Kevin G. Wagner" <w2fa at comcast.net>
    To: <amps at contesting.com>
    Sent: Wednesday, November 21, 2007 10:52 AM
    Subject: [Amps] [AMPS] Drake L-4 negative grid current reading on meter




      All,


         I'm having a problem with my Drake L-4 amplifier. A few weeks ago
      the .082 resister blew because one of the cap's let go in the power
      supply. I replaced all the cap's, diodes and the .082 resister in the
      power supply and whet to check out the amp. When I turned it on I
      have a negative grid current reading on the meter. It slams to the
      left at rest and when I key the amp it reads zero. I have purchased
      new tubes (3-500Z's) and I still have the problem. I then tried to
      calibrate the grid meter using the procedure in the Drake manual with
      no luck. I'm thinking it's a meter problem.
      Please help.


      73,
      Kevin
      w2fa






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  73,
  Kevin
  w2fa
  Cell     - 732-608-4749
  E-Mail - w2fa at comcast.net