[Amps] The transformer rosetta stone

[Jim Thomson]

Date: Sat, 03 Nov 2012 00:40:48 -0400
From: "Gary Smith" <Gary at ka1j.com>
To: Amps at contesting.com
Subject: [Amps] The transformer rosetta stone

Something different & something to show how much I don't understand.


I'm trying to understand something about transformers. What the heck 
is the rosetta stone for their nomenclature?

In specific; I learned the original single hole alpha 77DX 
transformer came with a "2.4 KVA CCS" rating. The two hole 77SX 
transformer came with a "4.4 KVA CCS" rated transformer.

OK, so looking at the Dahl specs I see their A77S transformer (one I 
used to have) to be "2800 VAC @ 1.2A CCS". The next higher voltage 
one in the catalog is a A77S-3 which is rated at "3000 VAC at 1.05 
CCS"

For the discussion, the Dahl filled in a lot of air space the 
original transformer left available. There wasn't much room in the 
enclosure once that transformer was seated.

I always thought the KVA came from V x I so if that's the way it is, 
I'm interpreting my old transformer to be 3360 KVA CCS and the other 
Dahl to be 3060 VAC CCS. If that's the case the Dahls have less 
cojones than the stock transformers but I know that's not the case, 
the Dahl was definitely a better performer than the stock transformer 
was.

This isn't making sense to me.

Gary,
KA1J

### beware, depending on  who writes the hype.  I have seen xfmr’s rated in CCS, ICAS,
and also IVS  ( intermittent voice service).  Ten-tec claims the xfmr in their Centurion 2 x 3-500Z
amp is rated at 3.5 kva CCS....and 7 kva IVS.   Yet the amp will barely do 1300 w pep out, and no
way will it do 1.5 kw CCS out on rtty-fm etc. 

## When the alpha 77 dx 1st came out...in the qst review, the xfmr was rated at 4.4 kva (dunno if that
was ccs, or icas).  That was a single 8877 amp.   As far as I know, the 77sx amps  with the 2 x 8877
lineup, also used the same 4.4 kva xfmr.   IE: they just stuck an extra tube in there, and used a 2:1 un-un
to make the oem tuned input work with the 25 ohm input Z of the two holer. 

##  Along comes dahl with his inboard xfmr replacement, and aprx 48 lbs.  If you wanted a real 4.4 kva CCS
xfmr, it’s  gonna weigh a helluva lot more than  46-48 lbs.   I have a 46 lb dahl xfmr, rated at 2750 vac @ 1 A CCS.
It also has lower taps at 1500-2000-2500.  It’s made for generic hb amp projects. 
Any 4.4 kva  CCS xmr would weigh aprx 69-70 lbs. 

##  Just take a look at his catalog, and you can tell by the various C cores he uses.  Each same size core, regardless of 
sec V + current ratings, is aprx the same CCS kva rating.   You want more power, move up to the next larger core. 

##  I suspect that the original 77dx core was rated at aprx 3 kva ccs....and 4.4 kvs icas.    Now compare that to the
‘3.5’  kva CCS  core used by ten tec, and it’s obvious to me that some amp makers have been drinking the cool-aid. 
There is no way in hell you can get 4.4 kva CCS  from a 48 lb xfmr, can’t be done.   And dahl does not go cheap on the
insulation, it’s rated for sky high temps.   Even with the good insulation, you still can’t obtain 4.4 kva  from a 48 lb xfmr,
that’s  just pie in the sky. 

later...... Jim   VE7RF