[Amps] Drake L-4B fan - too small and too slow?

[Gary Smith]

Hi Alan: if you can give me some specs on the fan in your L-4B, I can try to dig up some alternatives to the original fan as far as dimensional size and speed. If you need a faster fan speed, spec it and I'll take a hard look-see on this side of the pond.
73,
Gary... wa6fgi


 
  ----- Original Message ----- 
  From: R.Measures 
  To: Alan Ibbetson 
  Cc: amps at contesting.com 
  Sent: Wednesday, December 28, 2005 1:46 PM
  Subject: Re: [Amps] Drake L-4B fan - too small and too slow?



  On Dec 28, 2005, at 1:05 PM, Alan Ibbetson wrote:

  > Having replaced the 0.82 ohm fuse with a proper glitch resistor in the
  > HT supply of my L4-B, like y'all advised, I've been continuing to abuse
  > my Drake L-4B amplifier on CW.
  >
  > As I said a while ago, doesn't everyone run their old amps on the "SSB"
  > higher voltage setting? Well, maybe not with an L-4B! Mine runs too hot
  > to touch the top of the case after one or two of my rambling
  > transmissions.

  The L4-B needs a few V of cathode bias to reduce the ZSAC to something 
  reasonable.  A series string og fwd biased Si diodes can be used to 
  achieve this.
  >
  > I've upset myself by putting thermochromic labels on the sides of each
  > 3-500Z envelope. They've both gone black up to the 232 degree mark. 
  > This
  > is above the 225 limit on the plate seals and way above the 200 degree
  > limit on the base seals.
  >
  > First question: am I getting an accurate temperature measurement this
  > way?

  yes

  > Does the radiant heat from the anode hitting the back of the label
  > affect their accuracy?

  putting the detector adjacent to the anode stem glass-metal seal would 
  minimize this problem.

  > Even if my measurements are suspect, did Drake
  > really expect the top of the case to run so hot?

  The cooling system is not as well thought out as it is in the SB-220.
  >
  > Second question: why did Drake only fit a 2.5 inch 1550 rpm blower, 
  > when
  > Eimac suggest a 3 inch 3100 rpm unit? The Drake unit is made even more
  > puny by our 50Hz mains supply, which just compounds the problem.

  A brushless 12v DC motor would solve the problem.  It could be powered 
  by a FWD operating from the 5.5v filament winding.
  >
  > I could disable the factory blower motor, remove the fan blades, fit a
  > flange on the chassis rear, and plumb in an external blower I happen to
  > have here. But it's mechanically messy.
  >
  > Anyone know of a drop-in faster running motor that would save me 
  > burning
  > the paint off the top of the cabinet? Or is there a better way?
  > -- 
  >
  > Cheers,
  >
  > Alan G3XAQ
  > alan at g3xaq.demon.co.uk
  >
  > _______________________________________________
  > Amps mailing list
  > Amps at contesting.com
  > http://lists.contesting.com/mailman/listinfo/amps
  >
  >

  Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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