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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:05 am 
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Joined: Mar Fri 07, 2014 10:20 am
Posts: 1865
my mistake and I now have it hooked up right and I have a tone sorry


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:08 am 
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Joined: Mar Tue 13, 2012 6:56 am
Posts: 1014
Location: San Diego
No problem! Making mistakes and correcting them is part of the learning process.

Move the sig gen to the 6K7 grid cap. Do you have a tone at 462.5 kc?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:12 am 
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yes I have the highest tone at about 458


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:16 am 
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Great! Set the sig gen on 462.5 kc, then adjust the screws in the 2nd IF can to peak the tone. Only one screw will have any effect since we bypassed the other one.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:22 am 
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Joined: Mar Fri 07, 2014 10:20 am
Posts: 1865
done but I noticed the radio has a rumble in it at high volume


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:31 am 
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Ok, I wouldn't worry about the rumble for now. Could be a problem with the speaker.

I noticed that the 6K7 screen voltage (pin 4) is lower than it should be. It gets its voltage through R12. Check that resistor.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:36 am 
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the resistance is 34.9 k ohms and the resistor is made up of two blue grey orange 1/2 watt resistors parralle


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:41 am 
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Ok, that is exactly what it should be. While you are at it, check R3. Then re-measure voltages on 6K7, 6A8, and 6J5. Including grid caps.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:52 am 
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Joined: Mar Fri 07, 2014 10:20 am
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ok I will do that in the morning thanks again this is the first time I ever herd the radio like it was trying to bring in a station


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:56 am 
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Ok, great! We are getting there. :)

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 1:02 am 
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Joined: Mar Fri 07, 2014 10:20 am
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perfect I have all the faith in the world and no doubt you are one great teacher thanks


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 12:43 pm 
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Joined: Mar Fri 07, 2014 10:20 am
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r-3 15.59 k ohms tube 6k7 pin3 210dcv pin4 74 dcv pin 7 6.1acv tube 6a8 pin3 287dcv pin4 83dcv pin5 minus .4dcv pin6 76dcv pin7 6.1acv tube 6j5 pin3 83dcv pin7 6.1acv and that is all the voltages I read


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 6:07 pm 
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Ok, since we have some low voltages on the 6A8 and 6J5, let's check R13 (200 ohms), R1 (35k), and R2 (35k). The schematic is a little confusing around the 6A8: R13 is on pin 8 (cathode), and R1 is on pin 5 (oscillator grid). All these resistors can be measured without disconnecting them.

Also, I noticed a cap in the pic below that looks like it has not been replaced. Which cap is it? Are there any other paper or electrolytic caps that have not been replaced?

Attachment:
cap.jpg
cap.jpg [ 118.22 KiB | Viewed 440 times ]

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 6:12 pm 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Set the signal generator to 900 kHz, and connect it to the antenna terminals, and
try tuning in the tone by finding where it is on the radio's dial. Find how close it is
to 900 khz.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 7:23 pm 
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I am totally lost I have a resistor that goes to pin5 6a8 and ground that is 37.8 k ohms and have one from pin5 6j5 to a ground that also connected to pins 8 1 and 2 of 6a8 36.3k and that is all I see connected to those tubes and what you think is a cap is that 5kt resistor in the bypass and all caps have been done and has for the generator hook up I am not sure all the settings


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 7:47 pm 
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Ok, the schematic is different from your radio. On your radio, the 6A8 cathode (pin 8) is grounded, but on the schematic it is connected to ground through C18 and R13. I am guessing this was a production change and you have the earlier version of the radio. Let's try to get the radio working as is. Later we may want to add C18 and R13.

Steve has a good idea, but let's finish aligning the IF first. Keep the sig gen settings as they are on 462.5 kc and connect it to the 6A8 grid cap through a .001 cap. You should hear the tone. Turn down the Output Control on the sig gen to make the tone fairly faint. Adjust both screws in the 1st IF can to peak the tone.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 9:06 pm 
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Joined: Mar Fri 07, 2014 10:20 am
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i did the adjustments but found one of the screws one go in and out on the signal but I think I got it after but the radio still has only static


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 9:24 pm 
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Location: San Diego
Ok, can you explain in more detail what happened when you say "one of the screws one go in and out on the signal"?

Let's check the oscillator. I suspect it is not working. Leave the sig gen connected to the 6A8 grid cap. Set the radio dial on 600 kc and make sure push button #6 is pushed in for manual tuning. Scan the Frequency Adjustment on the sig gen. You will hear the tone at 462.5 kc but you will also hear it around 600 kc if the radio's oscillator is working.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 10:15 pm 
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Joined: Mar Fri 07, 2014 10:20 am
Posts: 1865
first the screw adjustment would turn a little and signal would come and go like a bad connection next I tried the generator and got signal on 462 frequency but went all the way through the rest but no tone also just for a try I went to both short wave bands and got one station on the middle band


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 Post subject: Re: marconi model 160
PostPosted: Jan Wed 11, 2017 10:50 pm 
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Location: San Diego
Ok, good news on picking up the shortwave station.

Sounds like the issue on the B.C. band is either a break in oscillator coil L1 (next to 6J5 tube, see below) or the bandswitch not making good contact. L1 has 3 lugs. Ohm it out: end to center, center to other end, and end to end. Also check resistance from 6J5 cathode to ground when bandswitch is in B.C. position.

Attachment:
L1.jpg
L1.jpg [ 80.39 KiB | Viewed 420 times ]

Matt


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