SB-610 Oscillator Problem

[W6CUX]

Hi Randy,
How and where are you measuring the SB-610 tone output? The
signal level at the output jack is very low -- similar to
the output of a microphone which it's supposed to replace.
There is at least a 100:1 attenuator between the tubes and
the jack. You should be measuring at the plates of the two
oscillator tubes (V4A&B). You should also replace the
cathode resistors as suggested by Mark.

The is no DC or ohmmeter path through the PEC.

I did a little reverse engineering on the PECs and assumed
that the resistors were 470K (same as the ones in the SB-101
and -401 PEC). My calculations make the capacitors 310 pf
for the 1500Hz PEC and 240 pf for the 1950Hz.

73, Stu W6CUX

----- Original Message -----
From: "Randall C. Iliff" <riliff at COMMSPEED.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Thursday, December 30, 2004 8:09 PM
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)

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