[Amps] New 2 PA design

[Baruch Zilbershatz]

Thank you for correction.
In Hebrew it is very easy...

Baruch Zilbershatz 
Nitzanay-Oz 118 
Nitzanay -Oz 
42836
ISRAEL 
phone: (+)972-052 8753838

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Roger (K8RI)
Sent: Sunday, October 17, 2010 8:21 AM
To: amps at contesting.com
Subject: Re: [Amps] New 2 PA design



On 10/17/2010 1:37 AM, Baruch Zilbershatz wrote:
> The DL guys that built that gizmo had it clamped with copper bars and
screws both sides to a copper heat sink .looks great.
> One guy made his own Al heatsink from folded Al strips and on top of it
had a copper heat spreader.

I hope you mean "on top of it" as meaning "in addition to". Copper, the 
better heat transfer material goes *under* the finned aluminum heat sink.
Putting the Aluminum first is like installing a resistor as it would 
limit the ability to transfer heat.

Actually this is an ideal place for water cooling and it doesn't take 
much. In addition you can even use chilled water.
The heat sink is at ground potential so the problems associated with 
water cooled vacuum tubes running high voltage are not encountered.

The best heatsink compound goes between the transistor and copper heat 
sink.  Using an all copper heat sink makes more sense than using a 
sandwich of copper and then finned aluminum except to save money and 
when you get into a project with expensive transistors, the cooling 
system is certainly not a place to try to save money. It's a place to 
save expensive transistors. Of course if copper is difficult to obtain 
in the required dimensions I can understand using a finned aluminum heat 
sink over the copper.  This might even be a good place to use the 
multiple "heat pipes" in an exotic configuration.

73

Roger (K8RI)
> Baruch Zilbershatz
> Nitzanay-Oz 118
> Nitzanay -Oz
> 42836
> ISRAEL
> phone: (+)972-052 8753838
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Paul Decker
> Sent: Sunday, October 17, 2010 12:20 AM
> To: amps at contesting.com
> Subject: Re: [Amps] New 2 PA design
>
>
>
> Hi Dan,
>
>
>
> You are right, heat and control are the primary issues to solve, and they
can be solved in a solid state design just as they are in a tube design.
>
>
>
> When the QEX article came out, I contacted JA1DJW about reproducing his
article.  He was very kind and sent me many emails with details, pictures
and some of the critical parts for the amp.    I think there are two
fundamental reasons the 2.5k isn't rated for full power output in continuous
mode.
>
>
>
> The first reason is the power supply isn't rated for continuous duty and
is maybe a bit under sized for the application.   A secondary reason would
be the heat issue.  Nobuik sent me a heat spreader but I opted not to use it
since the heat spreader is about 3.5" x 3.5" x 3/8" copper.   I opted to use
a 12 " x 8" x 1/2"   heat spreader with "copper fins"  attached and
replicated his machine work layout  onto it.   Efficiency is more along the
order of 60% at the worst, usually better though.
>
>
>
>
>
> Paul, kg7hf
>
>
>
>
>
>
>
>
>
> From: Dan Levin<dan at andlev.com>
> Subject: Re: [Amps] New 2 PA design
>
> The big issue with parts like the ARF-1500 is managing the heat.  For
> high duty cycle use, like contesting or RTTY (or worse yet, contest
> RTTY :-) ), you are dealing with dissipating something like 1500 watts
> of heat (assuming 50% efficiency running class AB) being generated in
> an area about one inch by three inches.
>
>
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