[HAM] Recapping generators - a few questions

[David Anderson]

On Saturday, August 19, 2006, at 03:57  PM, MarkTii at aol.com wrote:

> I've been pretty busy the last few months, so I've been lurking --
>
> For those who support recapping, what are the reasons and the theory?
>
> For those who generally oppose recapping, what are the  reasons?
>
> Are there times when those who generally oppose recapping believe 
> recapping
> is appropriate?

I've been busy lately and haven't been reading the lists, but I wanted 
to chime in on this one, having recently done some experimentation on 
the question.

Others have done a good job of discussing why the matching of capacitor 
values to filter inductors is important. The shortcomings of waxed 
paper capacitors were always known. I read one mid-1950s electronics 
textbook that stated that wax capacitors could be counted on to have a 
reliable service life of one year. Of course, many have lasted much 
longer than that.

In that context, I have a 1959 C-3 that has its original waxed paper 
capacitors, and I have no desire to recap it. It sounds great. On the 
other hand, I have a CV whose TG output levels on LC filtered tones are 
WAY down in comparison to the benchmark of the '59 C-3 I like so much. 
It had a kind of muffled character.

Waxed paper capacitors are sensitive to heat, heat cycling, and ambient 
humidity. Water that gets into the paper of waxed paper capacitors 
actually has a very high dielectric constant (something else I ran 
across in a textbook), so moisture infiltrating a waxed paper capacitor 
is probably the mechanism causing the increase in value.

As the capacitance value of a tuned filter goes up, the center 
frequency goes down, so as capacitors increase in value, the filter 
moves further and further from the frequency it's supposed to emphasize.

I would take the position that if it ain't broke, don't fix it. 
However, there may come a point where an individual generator's TG 
outputs 49-91 have dropped sufficiently to be less than one might want. 
It depends on the age of the organ but also the environmental 
conditions the organ has been exposed to. Of course, you'd want to make 
sure that the brightness you're missing isn't being lost in the 
preamplifier or tone cabinet. The drop in TG outputs is measurable on a 
meter or oscilloscope.

And if you don't want the organ to sound too "new," there is always the 
option of recapping a calculated amount *off* the ideal peak value. 
Nothing says that you have to peak each filter. It is perfectly 
possible to recap a TG to simulate a certain amount of capacitor drift.

David Anderson