[Heathkit] SB-610 phase networks needed

[Kenneth G. Gordon]

On 21 Sep 2007 at 15:08, K3PID wrote:

> The phase shift
> networks P.E.C 84-39 & 84-40 are the frequency determining components
> and my guess is that the internal capacitors have shifted enough to
> move the frequency.

Usually what happens with those PEC things is that the 
resistors drift HIGH, although the capacitors usually don't 
drift at all.

> Does anyone have these in NOS or if not then does anyone have the
> detailed specifications for the networks?

In some Heathkit rigs, the schematics show the values of 
the components inside that PEC, and then one can be 
made very easily out of discrete components. I do this 
regularly for the SB/HW transceivers which use a PEC as 
the tone generator for the CW sidetone.

As I said, in every case I have examined so far, the 
RESISTORS have drifted high, thereby raising the tone 
frequency. One of the main culprits is the (usually) single 
EXTERNAL resistor, which is also part of the phase-shift 
network. In the SB/HW transceivers, it is the resistor 
connecting the PEC to the tube.

As Sandy mentioned, there is VERY little information on 
designing those things. The math is not trivial, I might add...

Ken Gordon W7EKB