Help with Eico MX99 Multiplex Adaptor

[Eldin]

Hello everyone,

I currently have this adapter that doesn't properly create any form of separation in the channels, only mono audio from left and right.

I've followed the manual, and tried the adjustment procedures. The part where I adjust the T4 doesn't really make much of a difference in terms of distortion.

Would replacing all of the caps and try another alignment per-manual help this, or should I see if the 6D10 compactron is working correctly?

 

[knockbill]

Testing the tube couldn't hurt,,, easy thing to eliminate...

 

[s-petersen]

It could be your tuner as well, if you have not tried it on other tuners. Good separation depends on a good input signal of the proper input level.What tuner are you using it with?
When working properly, the MX99 is a great multiplexer, I have one someplace, along with a ST-97 tuner it is derived from.
Does the stereo light change from stereo to non stereo on different stations?.

 

[Eldin]

I'm using it with an h.h. Scott 311-d. Yeah on stations with no stereo FM the light remains off. I only have the one tube tuner to test it on.

 

[s-petersen]

That's a good sign... In the special instructions part of the manual, it mentions a cap that may need to be altered for non Eico tuners.
The other thing to remember is this was a kit, and may have some errors in it, I would follow the voltage test chart before proceeding .

 

[Eldin]

I'll try getting a few caps and trying a few things out, maybe I can get some separation. I think that cap just helps with separation that's already there though? I'm not getting any in the first place, even though the stereo light does come on. Thanks guys by the way.

 

[dcgillespie]

If the decoder has an input sensitivity adjustment, then understand that the Scott tuners are (by design) low output tuners at the output of the second (Ratio) detector. Therefore, you will likely need to (if possible) run the sensitivity of your MPX decoder at maximum. This is the reason that the Scott decoders used a pentode pilot amplifier stage -- this to elevate the signal to a level strong enough to lock the local oscillator under marginal FM MPX Stereo reception conditions.

I believe that the Eico MPX decoder is of the Matrix type, so adjustment will be critical for good performance.

Dave

 

[Eldin]

I'm still fairly new to tube gear and completely new to multiplex adapters. The input sensitivity wouldn't be one of the coils would it? I did notice that I had to run the scott at high volume for the stereo lamp to even appear on the eico when a station broadcast fm stereo. Based on what the manual says for lack of separation, i'm going to try replacing all of the caps and checking some key resistors.

 

[Eldin]

Just an update. Replaced all of the small caps, and all of the large ones in the can tested fine. Multiplexer works very well now, thanks for the help guys!