SB-610 Oscillator Problem

[Charles Seitz]

Yes,

I have been thinking about posting the same question for about a year now
but have not gotten around to it.

These are  phase shift oscillators that use cascaded rc networks within the
ceramic printed circuits to produce the 180 deg phase shift required to
sustain oscillation.

There's a small schematic of the inards of these on the SB-610 diagram
but the parts values are not given.  I suspect the final values are trimed
at the factory.  It shows no dc path between and of the pins so you
cannot check it with an ohm meter..

The dc voltages are all proper with my two tone oscillator.  I changed
tubes, checked ground lugs, cleaned tube socket contacts and cannot
get either section to work so I'm convinced the ceramic printed circuits
have failed.  The only problem with that theory is I have never seen any
of those kinds of devices fail in many, many years of electronics
experience.

When you solve the problem, please tell us about it.  There must be others
with the same problem.  I'll do likewise.

---  CHAS  WA2DYA



----- Original Message -----
From: "Randall C. Iliff" <riliff at COMMSPEED.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Thursday, December 30, 2004 23 09
Subject: SB-610 Oscillator Problem


Hi All,

I'm working on an SB-610 and for some reason neither oscillator will
function.  Parts are the right ones, soldering is ok, switch cleaned, tube
checked.  The cathode resistors have grown from 6,800 (heath value) to a
current value of 10,150 and 7,800 ohms respectively.  I can certainly swap
those out, and the 10 mfd caps that bypass them, with parts on hand but have
not yet done so.

Anybody else ever encounter a similar problem with these seemingly simple
oscillator circuits?

My concern is that the PEC phase shift networks seem to be open between pin
1 and 2.  (It seems odd to me that they'd both read that way, so maybe I'm
not measuring them properly.)

Anybody have the component values inside that overgrown ceramic package?  At
least then I could check these units or build up individual component
substitutions if they are bad.

Thanks, and best wishes for a wonderful new year!

All the best,

Randy (KE0BN)








On 12/29/04 1:44 PM, "w0akg1" <w0akg1 at EARTHLINK.NET> wrote:

> Some one has these made, I need one, thanks Guys.
> Martin Tippin WØAKG
> 31 Circle Dr.
> Windsor, Mo 65360
>
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