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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 7:17 pm 
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Check the center contact on the test lead where it screws into the generator, and the mating contact on the generator. Clean with a Scotch-Brite pad or scrape clean with a blade. Metal should be clean and bright. Double check continuity of test lead with your ohmmeter.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 7:27 pm 
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Also could be intermittent break in the center conductor where it is soldered to the connector. Can check center conductor continuity with your ohmmeter while flexing the cable. May need to unsolder, trim the end of the cable, and re-solder. Instructions here: http://crawlsbackward.blogspot.com/2016/07/diy-amphenol-mic-to-phone-cable.html

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 7:41 pm 
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I checked it all and even used two wires without the cable attached and the speaker and put one wire on centre and the other on ground and still no luck


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 7:54 pm 
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Inside the sig gen, clean the Output Selector and Output Multiplier switches carefully with a Q-tip and 91% isopropyl alcohol or Deoxit. Unplug the sig gen tubes one at a time and clean the pins with alcohol.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 8:45 pm 
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cleaned the contacts and working again and now on grid of 6q7 how do you want the generator set and what do you want me to do


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 9:07 pm 
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Ok, good. Sig gen red lead through .1 cap to 6Q7 grid cap. Output Selector: 400~AMP. Output Multiplier: 400~A.F. Do you hear a tone in the radio speaker?

If so, move sig gen (through .1 cap) to the point where the white wire is connected. Do you hear a tone that can be controlled by the radio's volume knob?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 9:26 pm 
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I clipped on to the end of the white wire and yes you can hear the tone and it is volume controlled


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 9:35 pm 
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Ok, very good. That means the entire audio section of the radio is working fine. Now try the IF again:

Switch the Output Multiplier to RF x 10.
Band selector on Band B.
Frequency Adjustment on 462.5 kc.

Connect red lead of sig gen through .001 cap to pin 4 of 6Q7 and listen for tone. May need to scan Frequency Adjustment between 400 kc - 520 kc to find it.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 10:05 pm 
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I tried it on pin 4 of 6q7 but had to adjust it to 100 r.f. and no matter how you adjust the frequency you still here the tone on the full broadcast band of the generator and it is volume controlled


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 10:15 pm 
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Ok good, we are making progress. Now try it through a .001 cap to the grid cap of the 6K7. (For all IF and RF tests use a .001 cap between the sig gen red lead and wherever you are injecting the signal.)

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 10:29 pm 
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I checked it on grid of 6k7 and nothing so I double checked generator and tried pin 4 of 6q7 and had a tone


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 10:42 pm 
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On grid of 6K7 did you try scanning the sig gen Frequency Adjustment?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 10:47 pm 
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at about 590 I get a very faint tone at best


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 10:57 pm 
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Ok, how about injecting to the plate (pin 3) of the 6K7? Of course be careful since the plate has more than 200V on it. Here it is especially important to have the .001 cap between the sig gen red lead and the 6K7 plate to protect the sig gen from the high DC voltage.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 11:06 pm 
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nothing at all on pin 3 of 6k7 and io scanned right through the frequencies and the output multiplier


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 11:19 pm 
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Ok, is there a wire from the IF transformer connected to the 6K7 pin 3 (plate)? If so, disconnect it and tape the end so it doesn't short against anything. Then try again injecting signal at the 6K7 plate.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 11:31 pm 
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disconnectted the if wire which only leaves the 5kt we installed for the bypass and tried and have no tone through all the frequency and rf multiplier


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 11:37 pm 
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Ok but on the 6K7 plate don't you also have the 2.0k resistor that you installed?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 11:44 pm 
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this is how I did the bypass first pin 3 6k7 has one end resistor 5kt it then goes to where the other side of l6 connects and from there I have one side of the 2.0k resistor and the other side of the resistor is connected to cap .001 and the other side of the cap goes to pi n 4 of 6q7


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 Post subject: Re: marconi model 160
PostPosted: Jan Tue 10, 2017 11:50 pm 
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No, the 2.0k resistor should be connected to the 6K7 plate. Go back and look again at the schematic on page 11 of the thread.

Matt


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