[Amps] L-4/L-7 Power Supply

[Michael Tope]

Hi Ed,

What you refer to as bleeder resistors are really part of a voltage 
divider that provides cutoff bias for the 3-500Zs. There are two 50 kohm 
x 50 watt resistors in series on the top side of the supply which are in 
turn in series with a 5K resistor on the bottom side. Each of the 50k 
resistors dissipates around 30 watts when the mode switch on the amp is 
in the SSB position.

Hi Ed,

I agree that the arrangement with the mica spacers is non-optimal. the 
bracket which is at ground potential has sharp points in close proximity 
to the high voltage on the resistor terminals. I was concerned about 
alignment when I installed the new resistors, but so far so good (I 
don't think the buzzing problem I have is related to voltage breakdown 
around these resistors).

73, Mike W4EF............................

On 2/16/2010 9:15 AM, Edwin Karl wrote:
> I'm not sure this is part of the answer to the problem with the buzz,
> but I think it's worth mentioning again to pass along to the folk.
> The bleeder resistor arrangement in this power supply is problematical.
> If you are not dead on when mounting the resistors so the screw centers
> in the center of the ceramic, it can lead to shorting out. The design
> calls for
> such an arrangement, and correctly reinstalling the mica insulator/ spacers
> between the mounting bracket and the resistor.
> I had a devil of a time with a buddy's amplifier until I got some nylon
> washers
> and screws to lift the mounting brackets off chassis ground. Using mica
> spacers
> and depending on alignment is not a good idea, IMHO. The breakdown of
> the resistor
> spacing is too close for comfort.
> Been working like a charm, only cost a couple of resistors that flashed
> over to
>   help with the prototyping.
> Good Luck, We're All Counting On You!
>
> ed K0KL
>
>
>