[Amps] Berkshire

[Manfred Mornhinweg]

Hi Bob,

> Why in the heck would anybody in their right mind even DESIGN or worse BUILD
> a voltage doubler power supply for their homebrew amplifier?

I will give you one reason, which was quite important for me, when I 
built amplifiers: I wound my own power transformers, because I could get 
the iron for free and the wire quite cheaply. Buying ready wound 
transformers instead, or having them wound to my specifications, would 
have been at least ten times as expensive. And when winding a 
transformer by hand, it's a BIG advantage to design for a voltage 
doubler: You need to wind only half as many turns, and the wire is twice 
as thick! The time saving is obvious, and the thicker wire is easier to 
handle and won't break so easily if the heavy thing slips away during 
winding.

The rectifier diodes are of the same voltage rating in both cases. For a 
doubler, you need half as many diodes, of twice the current rating. 
Given that the smallest diodes are for 1A average current, that's enough 
for the typical legal limit amp even when using a voltage doubler, so 
the doubling rectifier is cheaper than a bridge. You need the same 
number of capacitors, because anyway electrolytics hardly go above 450V 
each. The ONLY disadvantage of a voltage doubler is that you need more 
capacitance to achieve the same ripple. For me, the advantages, 
specially the much easier winding work, were worth the higher cost of 
filter caps.

Oh, I almost forgot: Thinner wire is more expensive by weight than 
thicker one, and you need the same weight of wire for both versions of 
the transformer. So there is an additional cost advantage (even if a 
slight one) to partially offset the higher cost in filter caps.

When looking at commercial amps, it seems that they have generally moved 
from doublers to bridges over the last few decades. I would guess that 
this is related to increased automation in transformer manufacture. When 
a robot winds them, the additional cost of winding twice as many turns 
of half as thick a wire probably no longer balances the higher cost of 
filter caps for a doubler!

Commercial manufacturers normally do things in the cheapest way that 
satisfies the requirements, and will not give preference to one or the 
other method just for matters of personal taste! They would soon be out 
of business if they did. Unless they can sell their particular whims to 
some group of golden eared hams who think they can hear a difference in 
the resulting signal!

Manfred.

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