[Amps] Centurion cooling improvement ideas for AM service

[Will Matney]

Rob and Gary,
Correct, that's why I mentioned earlier the plate transformer needs to 
be designed to handle at least 100% of the power that the carrier 
creates. If the transformer is sized to supply 50% of the peak power 
input, it will always be capable of sustaining the carrier at 100% duty 
cycle. The heater supply and control grid supply should be rated at 100% 
duty cycle, though. In most all large amps, these are supplied by 
separate transformers, but I have seen some wound on the same cores. All 
this needs to be calculated in at design time.

I always heard the controversy of the Heathkit SB-220's plate 
transformer being too small. I never did get a chance to reverse 
engineer one, but If I knew the core dimensions, and winding wire sizes, 
I could tell what they done pretty quick. I did always here by others 
that the plate transformer in the SB-220 actually did exactly what it 
was supposed to do if the amp was run correctly. If the core was a shade 
small, and they used at least 700 circular mils per amp on the wire, it 
should be ok. If they used 500 circular mils per amp, it might have got 
hot. At 500 circular mils per amp, 14 gauge wire is rated for only 7 
amps instead of the 15 amps for conduit rating. The problem is, the heat 
can't escape quick enough out of the tight coils and dissipate. So a 
minimum of 500 was devised by the transformer manufacturers. This is 
what you get from most "off-the-shelf" transformers. Amateur, and 
commercial equipment, is a horse of a different color when determining 
transformer sizes and power ratings.

One manufacturer that can be learned from is Hammond Manufacturing. They 
wind countless numbers of transformers for tube type audio service. I 
have reverse engineered several of their transformers by core size and 
Kva rating. All have came out to the same power rating as I calculate 
one. Most of Peter Dahls do too. Some of Dahls direct replacements do 
not however. I assume that they don't because they were wound by the 
original specs from the end equipment manufacturers. Keeping in mind 
that if the core size was made larger, the transformer wouldn't bolt up 
in the equipment! Without know what wire they used, I can't say if they 
raised the value or not. They can't that much as the coil couldn't fit 
in the windows of the core.

Will Matney