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Re: [Amps] Yaesu Quadra

To: David J Windisch <>
Subject: Re: [Amps] Yaesu Quadra
From: "Roger (K8RI)" <>
Date: Sun, 09 Mar 2008 19:00:14 -0400
List-post: <">>
David J Windisch wrote:
> Would this amp be a good platform for experimenting with an eye toward a 
> 1.5kW continuous output setup?
 From my view: Probably not.
I say this as these amps consist of a lot of very fast protection 
circuitry for over voltage, over current, over drive, a trip of 
reflected power, temperature, and most check to make sure the drive is 
on the proper frequency.
They use all this ultra fast detection and protection circuitry to 
protect what are often called the fastest fuses on three leads and those 
three legged fuses  are expensive.

Certainly there is *some* headroom built in. There has to be or the 
reliability would be nil.  How much head room is pretty much an unknown 
although a bit of research should turn up max voltage, current, and 
temp.  "I'd think" about the only place for any safe improvement would 
be in the cooling and I'd expect that to only allow  a marginal increase 
in power.  Depending on how careful you operate and nothing affects the 
antenna you could *probably* reduce the headroom on the protection 
circuitry. Unfortunately a broken element, insulator, or even a stray 
branch from a tree could put the system where one spike could wipe out 
one or all of the transistors.

Now if a person is willing  to spend money and in this case it's likely 
to be substantial (a relative term) for higher rated transistors to use 
in place of the originals AND play a bit with the impedance matching, 
then those voltage, current, and temperature limits could be adjusted 

I'm not familiar with the workings inside the Quadra, but my guess is 
most of these high power solid state amps are similar in  both the 
amplifier circuit and protection circuitry and when similarly equipped 
they have similar prices.  For example the 1.5Kfx is a bit less 
expensive than the Quadra until you include the external autotuner 
(which the Quadra has built in IIRC)  then they are about the same price.

I have the Tokyo Hy-Power HL-1.5Kfx which when running 1KW out (which 
happens ONLY when the SWR is 1:1) there is very little heat coming off 
the heat sink even in long winded QSOs. OTOH they do have an auxiliary 
fan for additional cooling when running RTTY, or slow scan.
> I am not concerned with resale value, since I never met a piece of ham gear 
> which couldn't be improved <BIGGRIN>
I believe several on here have, or are building up legal limit SS amps 
based on the 1.5 or 2.5 Kfx amps.  It's something I'd like to play with 
but just don't have the time.  Too many other projects.<:-))

73 and good luck,

Roger  (K8RI)
> Tia and & 73'
> Dave, N3HE 
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