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.
----- Original Message -----
To: Alan Ibbetson
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
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
> 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.
> 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
> 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,
> 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
> the paint off the top of the cabinet? Or is there a better way?
> Alan G3XAQ
> Amps mailing list
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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