Chapman/Derritron S6BS FM

[Murphyv310]

Hi
Jim is correct in both counts. The de-emphasis is indeed 50us and the circuit I posted is indeed for 75us. Hands up as I got it from a European site I wrongly assumed it was correct. A change of values will take a few minutes.
Anyway it works, I tested it on a portable with an MPX output and results were excellent with a little lack of treble that we know the reason for.
I'd already set up the 19khz oscillator with my AN8002 meter.
On the Chapman there was no stereo, audio was low level and with no bass. The reason was a bad mismatch, so next is a cathode follower in the tuner.

[Murphyv310]

Hi.
On the posted decoder diagram there is an error. The 47n is connected to Pins 3 and 11 not 13 and 11, no pilot if on the wrong pins.
I meant to correct this prior to posting up the circuit.

[Murphyv310]

Hi.
The addition of a FET follower has given me excellent results, audio quality is first class and the decoder switches to stereo on weak signals, even the noise level is acceptable on low level signals, BBC Radio 2 and the local stations sound superb with no detectable noise, stereo separation is very good.
I'm very pleased with the job and results.

[Murphyv310]

Hi.
Here is the Chapman in its home,  you can see the decoder to the right of the tuner,  its receiving BBC Radio 2 in stereo.