[Amps] How best to reduce filament voltage?

[Steve Cook]

Team,

Did anyone suggest using a length of 22ga Teflon wire to run voltage from the filament winding to the tube sockets.  I used this method in both of my TL-922A Kenwood amps.  Just trim the wires until the voltage at the tube sockets is where you want it (circa ~4.9V).

The wire runs barely warm to the touch and will not harm adjacent wiring in any way.  I have run my 3-500z class amps in this way for years with zero problems.

Steve (WG7K)
  ----- Original Message ----- 
  From: Norman Hockler 
  To: w2cqm at juno.com ; amps at contesting.com 
  Sent: Friday, February 02, 2007 7:48 AM
  Subject: Re: [Amps] How best to reduce filament voltage?


  Ron,

  Install a resistor on the primary side of the transformer.  Much 
  lower current and the resistors will act as a
  soft start for the filament to damp the inrush when you first turn on 
  power.  Set the resistor value with the
  tube on and warm  There are many sliding tap resistors available from 
  the distributors or a fixed one will
  work as well. Ohms law calculation to determine the value.

  de Norm N8NH

  At 08:16 AM 2/2/2007, w2cqm at juno.com wrote:
  >I'm building a single tube 3-500  6m amplifier around an OEM SB1000
  >transformer. The  Heath transformer is dual input 110/220VAC with HV,
  >filament(5vct), and 12VDC secondaries on the  common primary. The
  >original design of this transformer wound to accommodate the 3-500.
  >The problem is that the filament secondary appears to be overly high
  >and measures 6.5VAC no load and 6.09vac with the tube installed. Since
  >there's an exponential loss of tube life with only minor filament
  >overvoltage, I'm caught between a rock and a hard place. In this
  >instance, the obvious answer is to install a dedicated filament
  >transformer correctly designed for the application; however, that
  >involves an additional (redundant) component. The question is whether
  >it's somehow practical to reduce the filament voltage without getting
  >involved with an odd ball low ohmage, high wattage resistor series
  >installed on the secondary. Any comments would be appreciated. Ron
  >W2CQM/3
  >
  >.
  >
  >_______________________________________________
  >Amps mailing list
  >Amps at contesting.com
  >http://lists.contesting.com/mailman/listinfo/amps


  _______________________________________________
  Amps mailing list
  Amps at contesting.com
  http://lists.contesting.com/mailman/listinfo/amps