[Ron Ramirez]

OK Mike (morzh)

I decided to take a little time to trace the audio with a scope this morning.

Plugging in headphones so the amp would have a load, I injected a 10.7 mc signal at the input of the IF board, modulated at 400 cycles.

I connected the scope from the negative of C29 (1500 uF) to ground. C29 couples the left channel audio from the output transistors to the speaker terminals.

The waveform was clean as a whistle.

I did the same thing at C30 (right channel).

Clean.

Next, I connected the scope to the left "main" speaker terminals:

[Image: http://www.philcoradio.com/images/phorum...0-T_01.jpg]

Then the right "main" speaker terminals:

[Image: http://www.philcoradio.com/images/phorum...0-T_02.jpg]

Then, I connected the scope to the left "remote" speaker terminals and changed the speaker switch from "main" to "remote":

[Image: http://www.philcoradio.com/images/phorum...0-T_03.jpg]

Now, right channel "remote":

[Image: http://www.philcoradio.com/images/phorum...0-T_04.jpg]

Although the right channel's amplitude is somewhat lower than the left channel (this is with the banance control set to zero), note that the signals are clean.

Something interesting happens when I hook up speakers, though.

Left channel:

[Image: http://www.philcoradio.com/images/phorum...0-T_05.jpg]

Right channel:

[Image: http://www.philcoradio.com/images/phorum...0-T_06.jpg]

See the pronounced distortion?

The distortion is not present at the output of the control amplifier board, but is present from the outputs of Q11/Q12 on through the final audio amplifiers. It is as if this receiver does not like speakers.

Side note: It sounds fine with headphones now. But when speakers are connected, the sound is heavily distorted.

I have a 170-T which has this same problem, so I am hoping that if I can find the answer to this 440-T distortion issue, that I will also be able to fix the 170-T.

You will be wanting to see the schematic. Here it is (3.3 MB):
http://www.philcoradio.com/images/Fisher..._SCHEM.zip