[sdiy] ARP 4027-1 VCO cloning?

[Dana Scott]

Those are all standard 1% values.  The FETs ARP used were 2n5459's that were
selected for a low pinchoff voltage. You can use 2n4392's with guaranteed
results.
You might have a little trouble finding the 2n5910 transistor. If you use
something with a different switching speed you will have to adjust the
resistors that are in the compensation loop. They are 2 equal value
resistors with a .01 to ground in the middle. Can't remember the resistor
values, probably 61.9K or 100K if I had to guess.
I had an email from someone, probably on this list, that had 1.87K tempco's
for sale( rather high price IIRC).
The TZ81/TZ581 expo pairs can be replaced with 2n3904/2n3906 pairs. No
selecting or matching was done by ARP, Just replace the expo pair if it does
not meet spec.
Somewhere in my pile of ARP stuff I have a 1:1 film negative of an early
4027-1. Not sure how I could copy it for you.
I also have a copy of the ARP factory testing fixture schematic for the
4027-1 and a copy of the test procedure if that is of any interest.

-Dana
ARP Production Engineer 1974-1980


Subject: Re: [sdiy] ARP 4027-1 VCO cloning?


> > 61k9,121k,30k1,45k3,33k2,8k87,1k65,....and all of them 1%.
>
> You could use trimpots. (100K, 250K, 50K...)
> --
> john
>