[time-nuts] Cheap 9.8Mhz Sa.22c's

[Charles P. Steinmetz]

David wrote:

>I hadn't thought about the uA739 for a while.  It was one of the 
>original low-noise amps - we used to use it for phono preamps.

If you could live with the anemic output drive, they were great 
opamps for the time.  I preferred the 749, which had an 
open-collector output (no 5k internal pull-down resistor).  I often 
used external current source pulldown, bias network, Schottky Baker 
clamps, and Class AB complementary emitter-follower outputs.  Once 
when 749s were unavailable but 739s were plentiful, a Fairchild 
engineer taught us how to open-circuit the 5k resistor cleanly to 
turn 739s into 749s.  The plastic DIPs were prone to 
sealing/passivation problems, so we always bought the ceramic parts 
(I pretty much always customized the compensation, so we couldn't use 
the 8-pin hermetic parts).

>Re: glass piston caps, I have been able to sometimes get what I need 
>from Surplus Sales of Nebraska

You can get ceramic piston trimmers from the usual primary 
sources.  For example:

http://www.spraguegoodman.com/pdfs/660.pdf
http://www.eyou.com.au/product/johanson-5202-rf-air-trimmer-capacitor-08pf-10pf-/
http://www.johansonmfg.com/pdf/Air-Capacitor.pdf

Eastern European clones show up regularly on ebay at much lower 
prices.  The ones I've bought have been made to high standards and work well.

I think glass piston trimmers are still available from primary 
sources, too, but I don't have a link handy.

Best regards,

Charles