VCO4d

[tomg]

> I found 1 Clairex 100k tempco in my spares box.  I haven't used one in
> ages .  I want to try using this component instead of the heater in my
> vco4ds.  How should I apply it to this circuit ?  Where can I get 9
> more?

You need a 1K 3500ppm T.C. for the tempco option. I think Paul S. still has

those for $5.00 ea minimum of 5. Still got 'em for sale Paul? Jorgen says
he 
gets them from Farnell (sp?) for $.80 ea., if you can order from Farnell?? 

> The heater option looks quite involved and would not be fun to get 8 to
> respond identically unless there is a way to match the 3046s.  I've
> matched tubes & transistors before but I don't know how to do chips.

It's not really that involved. For +/-12V use 2-220 ohm 1/2 watt resistors
for +/-15 use 2-330 ohm 1/2w. If the chip heats up to the point you 
can't keep your finger on it increase one of the resistors by another 100
ohms. +/-12 1-220 and 1-330 , +/-15 1-330 and 1-470. Once this is set
you never have to mess with it again. The chip should not be hot just
nice and warm to the touch. 

Can't match 3046s (well maybe you could but you might match 2 out
of 20)...but It shouldn't matter. Just heat 'em up. Once they reach a 
more than ambient temperature, then tune them. I would do one as a
master then tune the rest one at a time to match it. 

If your 100K T.C. is negative you might try replacing R11 (it's now a 1K5)
it will change the center frequency but it might work. BTW if you replace
R11 with a pair of 1M 1% and a switch you can have 8/16/32 footings.
R11 = 0 for 8' , = 1M for 16' = 2M for 32'.

-tg