REL Precedent detector

[cpu_]

I have been studying the discriminator circuit in the REL Precedent 646C-1 tuner. I would like to understand this circuit better. It's a ratio detector, according to REL literature. Here is an excerpt from the schematic.





The schematic depicts an arrangement that differs from the usual schematic of a ratio detector. The primary inductance (connected to the plate circuit of the final limiter, a 6AH6 tube) is shown with connections to two other windings. Ratio detectors usually have a transformer with a center-tapped secondary winding, and a tertiary winding. In this depiction, it isn't clear which winding is a secondary, and which is a tertiary. Whatever the case, all three windings are connected at the "hot" end of the primary.

A description of the physical arrangement of these coils and the coupling and phasing would be welcomed. Has anyone opened the shield can of one of these transformers?

Another question: Were these transformers made by REL, or were they sourced by another vendor?

 

[amptramp]

Even with the reversed diodes, this is a discriminator, similar to the one used in the Dynatuner. Leading phase pulls the signal at the junction of the two 4700 ohm resistors in one direction and lagging phase pulls it in the other. A ratio detector has the two diodes in series driving their output into an electrolytic capacitor so that when the signal rises, the capacitor is a significant load and when the signal level drops, the capacitive load is reduced or taken away entirely - that is how a ratio detector maintains a steady signal when the signal level fluctuates and that does not exist in this detector.

 

[Joe Roberts]

It looks like a ratio detector without the AM suppression electrolytic. Note that the Precedent has many limiter stages so AM may have been well squashed before it hit the detector.

The difference between that REL schematic and a "typical" ratio detector is that instead of a primary and center-tapped secondary with a tertiary winding picked off the CT, this one uses a center tapped autoformer (still a transformer) with the tertiary winding attached to the CT.

Coils in that tuner look like standard Miller type units but may have been custom manufactured. I'm not prepared to take mine apart!