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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 11:13 pm 
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the resistance from cathode of 6j5 is 1.0 ohms to ground but if I am looking at l1 correct it is a square box with the screw in the centre and two lugs at each end or is it a wire wound coil with three lugs


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 11:19 pm 
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here is a picture


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DSC00134.JPG
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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 11:31 pm 
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Oops, I posted the wrong chassis diagram! L1 is this coil with 3 lugs:

Attachment:
B.C. osc coil L1.jpg
B.C. osc coil L1.jpg [ 170.71 KiB | Viewed 473 times ]

One of the lugs of L1 is grounded, the center tap goes to the bandswitch, and the other end goes to the bandswitch and pushbutton switch #6.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 11:56 pm 
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brown goes to band switch, green to push button, brown to green .9 ohms, brown to ground .8 ohms, and ground to green .0 ohms


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 12:15 am 
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This looks like a ground wire attached to the lug where the green wire and the mica cap are attached. Is this wire soldered to ground? If so, it should not be there. Clip it and see what happens.

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B.C. osc coil ground wire.jpg
B.C. osc coil ground wire.jpg [ 168.7 KiB | Viewed 469 times ]

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 12:21 am 
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I will check this out in the morning but with that being said I checked continuity from the antenna wire screw to chassis ground and found that there was continuity and also to the oscillator frame also so is this normal


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 12:57 am 
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I assume you mean the frame of the tuning capacitor? If so, the answer is yes to both. Take a look at the schematic below. Anytime you can find a path to ground through wires or coils, you will have continuity. The path cannot go through a capacitor.

From the antenna terminal, the path (yellow) goes through two coils on the way to ground, so you would measure the total resistance of those coils. The frame of the tuning capacitor is directly grounded (blue).

Attachment:
continuity to ground.jpg
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Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 1:12 am 
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thanks now I understand and I will check that ground wire in the morning


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 12:04 pm 
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I cut the ground wire off and has you suspected the radio is now working but not right I get a muffled sound when I turn volume all the way up and shortwave is poor at best


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 12:30 pm 
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Shortwave will be poor without a decent antenna and if it is not aligned properly, both being accumulative. Audio distortion is likely a unrelated (to the front end) albeit if the total alignment is out, that won't help.

Marc


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 4:43 pm 
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Ok, great! Re-measure voltages at 6A8, 6K7, and 6J5, including grid caps. Also, what voltage do you measure directly across the bias cell (one voltmeter probe on each side)?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 5:05 pm 
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6a8 pin3 286dcv pin4 130dcv pin5 minus 6.58 dcv pin6 95dcv pin7 6.1acv 6k7 pin3 182 dcv pin4 94dcv pin7 6.1acv 6j5 pin3 132dcv pin5 minus 8.30dcv pin7 6.1acv and the bias cell had .49 dcv


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 5:24 pm 
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Ok, the bias cell needs to be replaced, although I am not sure if that is causing the distortion. Should be 1.5V. Did you order any of those watch battery holders from ebay?

Disconnect the radio's antenna and use the sig gen to inject an audio signal (Output Multiplier on 400~A.F.) to the 6Q7 grid cap. Do you have the distortion then?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 6:34 pm 
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yes I get distortion when I hook the generator up to 6q7 grid and no I did not get any battery holders yet but I can hook up a round aa battery if that will wok


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 6:58 pm 
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I would not use a AA battery. Get one of these: LR44 Battery Holder

Since the distortion is there when injecting at the 6Q7, it doesn't look like the bias cell is causing it. Might be the speaker. Unsolder the speaker wires (below) and connect a permanent magnet speaker to check.

Attachment:
speaker connections.jpg
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Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 7:28 pm 
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I disconnected those two coated wires plus what looked like a ground wire and hooked them up the same way has the other speaker was and got nothing only something arching out in the radio and no sound


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 7:38 pm 
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Can you take a picture showing how you have it hooked up?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 7:41 pm 
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I can but I tried again I guess the radio was not tuned in right but that being said I only get a faint sound from both speakers


Last edited by spsquires on Jan Thu 12, 2017 7:44 pm, edited 1 time in total.

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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 7:44 pm 
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Try disconnecting the ground wire that you mentioned.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 7:46 pm 
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I just tried and still get sound in both speakers


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