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[Amps] Quadra step start

To: <amps@contesting.com>
Subject: [Amps] Quadra step start
From: "Jim Thomson" <jim.thom@telus.net>
Date: Wed, 26 Apr 2017 08:53:01 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Date: Wed, 26 Apr 2017 08:38:44 +0100
From: "Ian White" <gm3sek@ifwtech.co.uk>
To: <amps@contesting.com>
Subject: Re: [Amps] Price per Watt Conversation
K8RI wrote:

>At close to 200W per device, it would require 8 devices in a circuit
>much like the Yaesu Quadra, but with a legal limit out for less money.
>BTW I saw several posts praising the Quadra, but the Quadra has several
>inherent problems in the basic design according to the Yaesu news
>groups..  One is the PS is designed for 220 VAC and not the current
>standard of 240 leading to a number of failures. Another is the way the
>power supplies feed the individual amps. OTOH it is a nice amp and I do
>see a number of hams claiming to be running 1200W out for many years.
I
>have two.

The main problem with the Quadra PS is its tendency to blow the
step-start resistors (R2A, B, C) that limit the startup surge current.
This is caused by two design errors, both of which can easily be
rectified at repair time.

1. Step-start resistors are overloaded by design, but the cement-cased
resistors that Yaesu selected are quite poor at handling surges! If they
fail, replace all three with glass-coated resistors with better
surge/overload characteristics.  

2. If the step-start relay fails to activate for some other, unrelated
reason, then the step-start resistors *will* blow because they have no
other protection. Following an idea from Alpha, insert a time-delay fuse
that is rated to blow in several seconds. (This idea will not work with
the existing Yaesu resistors... guess why.)

73 from Ian GM3SEK

##  did yaesu ever fix the problem..or are they still building it wrong ? 
I have seen all sorts of ..fixes for that amp, and many included using a
20 vac buck xfmr, to knock down the 240-250 vac  by 20 vac. Some other
schemes used a 240 to 220 xfmr. Some used a big variac. 

##  the simple fix is to replace the step start resistors  with real ones, even
the metal finned arcol types should work.   Alpha use a slow blow 3agc type
fuse in series with the step start resistors.  So if the shunting relay did not 
operate,
the fuse would blow instead, saving the step start resistors from being 
destroyed.
B+  would then  drop to zero. 

##  another issue with that amp was the  external power supply is supposed to 
be turned on...
1st.   Then the RF deck is turned on next.   If the RF deck is turned on 1st, 
followed by the
power supply next, then a load is placed on the power supply, further 
increasing the load on the
step start resistors.  That would also happen if the commercial AC power went 
off.  When the
commercial C power came back on..and both power supply +  RF deck already 
switched 
on, the combo would stress the step start resistors.   Cement cased 
resistors...  wtf  were they 
thinking.   What else did they do to enhance profits ?    Correct type and 
wattage step start 
resistor, you only require one resistor, or 2 if space constraints, is all that 
is needed.... plus
a 3agc fuse holder + mating correct sized slow blow fuse. 

##  240 vac / 50 ohms =  4.8A =.....  1152 watts 
240 vac / 20 ohms =   12 A.....  = 2880 watts.
240 vac / 10 ohms = 24 A......    = 5760 watts. 

##  as u can see from the above step start resistor values, this is no
place for a cement cased resistor.   When T=0..... u have one helluva
lot of instantaneous power being dissipated in the resistor.   And if the
relay contacts shunt out a blown open step start resistor, then kablamo,
no step start protection at all.   So the vdc has to be monitored in the case
of either an open step start slow blow fuse.... and or an open step start
resistor. 

Jim  VE7RF 


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