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Re: [Amps] Buck-boost xfmr

Subject: Re: [Amps] Buck-boost xfmr
Date: Thu, 26 Jun 2014 11:26:54 +0000 (UTC)
List-post: <">>
I've never seen, or heard of, the primary supply section in the power supply 
fail - for any reason. The problem with the supplies is that there is an 
approximately 12V "sub-supply" that feeds the control subsystem (to provide 
remote on/off control from Yaesu transceivers) that is regulated and protected 
through three "fuse resistors". These will, by design, fail if exposed to 
excessive voltage, are a gigantic pain to find today and will prevent the amp 
from working if they open. They're not so much sensitive to sustained voltage 
near the published limits as they are transients, which cause them (by design) 
to open, thus preventing the entire amp from operating. 

I ultimately ended up buying a surplus marine AC line conditioner to protect 
everything in my shack from the lousy power from our utility company. I only 
had this occur once to me, but this "sub-supply" is a glaring design compromise 
and needs to be protected. It's a gigantic pain to disassemble the "origami" PS 
internal enclousure and board assemblies, and about a $500 repair to send to 

Again...the thing to protect against are transients. 


Mike - N8MSA 

----- Original Message -----

From: "Jim Thomson" <> 
Sent: Thursday, June 26, 2014 6:32:43 AM 
Subject: [Amps] Buck-boost xfmr 

Date: Wed, 25 Jun 2014 21:41:36 +0100 
From: David Lisney <> 
To: "" <> 

Hi, the power supply for the Quadra is a switch-mode, the manual seems to 
reckon 240v is ok. 
In the UK our mains voltage is 240v, as far as I know Quadras survive that 
fine... I personally would run it straight off your mains supply... the buck 
transformer is a valid approach to sorting out the supply voltage issue... 
however it is vital that current is not allowed to pass through the low voltage 
secondary without the primary powered. 
A 15v 10a transformer should do the job... 
regards David G0FVT 

## I see no reason why a 10-15v @ 15A CCS xfmr cant be used.... with NO 120 vac 
applied to the 120 vac primary of the buck-boost xfmr. All that would happen is 
you wont get any boost-buck action. 
If you really want to get fancy, you can always install a small 0-120 vac 
variac, say a 2A CCS variac, on the primary side of the buck-boost xfmr..and 
vary the amount of buck-boost you want... from 0-15 vac in this case. 

## Having said all that, has anybody actually blown a Quadra up.....from line V 
being too high ??? I could see transients-spikes-surges etc, blowing it up.... 
but that is something that could be averted with movs at the main 200A panel 

## Interesting to note that the old Q manual sez its rated up to 234v. New 
manual sez its rated to 240 vac. Wonder if they just changed the manual ? 

## If you folks do try a buck-boost xfmr, make damn sure its wired for 
buck..and NOT boost... or you will be in for a rude awakening. Test the xfmr 
out on a 100 watt light bulb 1st... + DVM. 
## Does yaesu still make the quadra ? I see Acom has its 600 w SS amp in 
production....which will handle just about any line V you can throw at it. It 
also has power factor correction built into it. But at $3K a copy, I think I 
will pass on it..esp with the lousy IMD. 

Jim VE7RF 

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