[Top] [All Lists]

Re: [Amps] Buck-Boost Transformer Selection

To: "'Richard Solomon'" <>, <>
Subject: Re: [Amps] Buck-Boost Transformer Selection
From: "Jim Garland" <>
Date: Wed, 25 Jun 2014 22:42:10 -0600
List-post: <">>
Hi Dick,

I believe you are misinterpreting the KVA rating in the table. The KVA refers 
to the power dissipated in the load (i.e., your amplfier) and not the KVA 
rating of the buck-boost transformer. The actual power rating of the 
transformer is just the current through the secondary times the number of 
bucking volts supplied. 


For example, let's say your actual line voltage is 250V and the amplifier draws 
14 Amps, which correspnds to a power rating for the amplifier of 3.5KVA. (That, 
by the way, is the peak power. The average power is probably about half that.)  
Now suppose you want to reduce the line voltage to, say, 238V, and we'll assume 
the amp still draws 14 Amps at this lower line voltage.  You are bucking the 
voltage by 250V-238V = 12V. The bucking transformer will then have to carry 14 
Amps of current, so its power rating will be 12Vx14A=168W. An ordinary filament 
transformer with a 240V primary and a 12V secondary rated at 14A would be 
perfect for this application.  I wouldn't buy the Hammond buck-boost 
transformer, because you'll be spending a lot of money unnecessarily. The 
Hammond transformers are designed for industrial, continuous duty application 
at full rated load. You'd be paying for a lot of capability which you don't 
need. Personally, I'd think a 12V filament transformer rated at
  10A or more would be adquate for your amplifier.


There is one more consideration, which may complicate things slightly. If your 
amplifier is designed for the US market, it may require a neutral line which in 
the US is at 0V, with the L1 and L2 lines each being 120VAC (out of phase with 
each other). Most likely, that's not the case with a Quadra, but you should 
check to be sure. If you do require a neutral line, then you'd need two 
filament transformers, each having half the required voltage rating ( e.g. 6V 
instead of 12V). It's a minor complication.


In principle, you could also use a Variac,which is an autotranformer, to get 
the reduced line voltage, although I don't recommend it. Unlike an ordinary 
transformer, which has a primary and secondary winding, an autotransformer has 
only one winding. A slider on the winding (or a fixed tap) picks off the 
desired voltage. You do not want to use a Variac for your situation, because 
the full line voltage appears across the variac, which means you'd need a 
variac rated at 3.5 KA. That would probably weigh about a hundred pounds and 
would be very expensive. A variac would be gross overkill merely for reducing 
the line voltage for your amplifier.


I get the impression, Dick, you are making this a harder problem than it really 
is. All you need is a filament transformer whose secondary voltage will drop 
your line voltage by a few volts, to get it into the recommended range for your 
amplifier.  You can probably find a dozen or more suitable transformers on eBay 
or for well under $50. 


Jim W8ZR



From: Richard Solomon [] 
Sent: Wednesday, June 25, 2014 9:37 PM
To: Jim Garland
Subject: Re: [Amps] Buck-Boost Transformer Selection


I found this web site while looking up how to connect the transformer.

According to it, using it with the Quadra (14 Amp @ 240 vac), I need a 3.5 KVA 

That's quite a bit larger than what you say I need.

Still confused ... 

73, Dick, W1KSZ



On Wed, Jun 25, 2014 at 10:17 AM, Jim Garland <> wrote:

Hi Dick,
You don't need a 1.5KV rating. Let's say you want to drop the line voltage
by 12V and suppose  the maximum current drawn from the AC line by the
amplifier is 15 Amps. You'd thus  need only a 12Vrms/15A transformer (180W).
Because of the limited duty cycle of the Quadra, probably a 10-12A
tranformer would work fine.
Jim W8ZR.

> -----Original Message-----
> From: Amps [] On Behalf Of Richard
> Sent: Wednesday, June 25, 2014 11:06 AM
> To:
> Subject: [Amps] Buck-Boost Transformer Selection
> I have a lead on a late production Quadra so I guess I better
> invest in a B-B Xfmr to get my sometimes 250 volt line down
> to something acceptable to my new little friend.
> Question is on the rating for the Xfmr ... I expect I should get
> something rated for the load, say 1.5 KVA (considering the
> rating is for CCS use not ICAS).
> Now I find lots of them over on the evil empire, but looking at
> the specs on the label is confusing:
> One I found says:
> Max Volts 264   Max Amps 62.5  1.5KVA
> The current rating does not make sense. How can I sort this out ??
> Thanks, Dick, W1KSZ

> _______________________________________________
> Amps mailing list


Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>