[sdiy] Oscillator caps - please help!

[JH.]

Polyester is no good; Polystyrene ("Styroflex") would be my first choice.
You can often find them on ebay, even in odd values.
If not, combine two caps in parallel connection to get the desired value.

JH.

----- Original Message ----- 
From: "Antti Pitkämäki" <anpitkam at hotmail.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, August 14, 2007 9:59 PM
Subject: [sdiy] Oscillator caps - please help!


Hello everybody,

I'm currently having a project of fixing a Vox Super Continental (UK model)
combo organ. I have decided to first order every part that I could possibly
need before starting the project. However, I have a problem. The 12 master
oscillators of the organ each has a coil, and two caps. Of the two caps,
other one has the value 0,1uF on every card, and the other cap has a
different value depending on the card. Now the thing is, that I've heard
that you must use polypropylene caps in oscillator circuits like these, so
that the tuning is stable and doesn't drift so much with changing
temperature. Unfortunately it seems to be impossible to find replacement
polypropylene caps that have the right value. For example, the value of 82nF
(0,082uF) is used several times. So this has made me wondering... Maybe the
organ doesn't use polypropylene caps in the first place? Maybe I have been
misinformed? I did find replacement 82nF "Metalized Polyester Film" caps -
could I use these for example? What caps would you use? I guess I could try
to come up with the correct values by combining several polypropylene caps,
but maybe I don't need those kinda caps? Please help :) I know that my
question is a very basic question, but I gotta be a beginner before I can be
a guru :)

Antti P.

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