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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 12:26 am 
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What does the noise sound like? Is it static or hum or ?

Measure voltages on 6K7 and 6Q7 again and post them. Also voltage on pin 4 (screen) of 6F6.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 12:33 am 
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will do that in the morning thanks


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 11:45 am 
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the noise is a hum with the accent of trying to bring in a station in the background and the voltage is tube 6f6 288 and 287 dcv on pins 4 and tube 6k7 pin 3 207 dcv pin 4 76 dcv pin7 6.1acv tube 6q7 pin 3 62 dcv pin 7 6.1 acv also I noticed when I turn the radio on and off I get a what sounds like a power surge and you can here a hum in power transformer


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 12:02 pm 
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The sound you hear at turn on might be loose laminations in the transformer. It won't hurt anything but, if it bothers you, you can try tightening the bolts that hold the laminations together. Beyond that, there is a fix that takes a bit more work.

I'd get everything else working first.

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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 4:10 pm 
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Which resistors did you wind up using when you built the circuit? Also measure voltage on pins 4 and 5 of 6Q7 as well as on grid caps of 6Q7, 6K7, 6A8. Listen for crackle in speaker while measuring voltages.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 4:54 pm 
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the resistor was the 5kt 5watt and pins 4 and 5 of 6q7 has no volts and the grid of 6q7 has minus .61 dcv and a crackle in the speaker and the grids of 6a8 and 6k7 has minus 1.0 volt on grid and no crackle sound


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 5:23 pm 
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Turn off the radio and measure the resistance across the 15k 5-watt resistor. Also, did you use a 2.2k for the other resistor?

Do you have another 6K7? If so, try switching it out to see if there is a difference. Measure voltage on grid cap and listen for crackle.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 7:41 pm 
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Use the audio output of your signal generator to inject a tone into the grid of the 6F6.
Then move it to to the top cap of the 6Q7.

Then use a modulated 462.5 kHz signal to pins 4 and 5 of the 6Q7.

Then move back to the grid cap of the 6K7 with the modulated 462.5 kHz. signal

As well, with the radio off, what is the resistance between pins 3 and 4 of the 6F6 ?

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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 8:03 pm 
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I used a 2.0 k resistor and the resistance on the 15 k is 15.23 k ohms and the resistance on pins 3and4 of 6f6 on both tubes is .344 k ohms and I tried another 6k7 but the voltage is still 207 with a little crackle and has for the signal generator I am not sure . I have a Hickok 288k but uncertain how to set it up


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 8:14 pm 
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Ok, good. Steve has a good idea on using the sig gen at this point, but I think the audio stages are fine, so let's go directly to the IF stage.

Set the sig gen as follows, just as it was set up when you were working on the Marconi 157:

Frequency Modulated Sweep - Turn clockwise to switch on sig gen, pilot light should light up. Knob setting does not matter.
Band Selector - B
Frequency Adjustment - Turn until dial pointer reads 462.5 kc on B band
Output Control - 50
Output Multiplier - RF x 1
FM-AM Selector - Amplitude Modulated
Output Selector - 400 ~ Amp.
Variable Audio Frequency - Knob setting does not matter

If you have an antenna connected to the radio, disconnect it. Connect the sig gen black clip to chassis ground. Connect the sig gen red clip to a .001 uF cap, and connect the other side of the .001 uF cap to the 6K7 grid cap. Switch on the radio and the sig gen. Turn the radio volume control up loud. Do you hear the sig gen tone through the radio? If not, adjust the Output Control knob between 0-100 and the Output Multiplier to RF x 10 or RF x 100 as necessary. You should adjust the sig gen so that the tone is faint but still audible through the radio.

Then adjust trimmer on 2nd IF can for maximum loudness of tone. Turn the sig gen Output Control down to keep the tone faint. Only one of the trimmers should have an effect since we bypassed the other one.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 8:46 pm 
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I tried the generator but I can not get any tone at all in the radio


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 8:55 pm 
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Use the Frequency Adjustment knob on the sig gen to scan the frequencies from 400 kc - 520 kc to see if you hear the tone at any point.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 9:20 pm 
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still no tone in the radio


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 9:23 pm 
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Move the sig gen .001 cap from the 6K7 grid cap to pin 4 of the 6Q7 and see if you hear the tone there.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 10:16 pm 
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still nothing only I get static when I change the output control knob and I can also here the changes when I change the output multiplier


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 10:28 pm 
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Double check that Output Selector knob is set to 400 ~ Amp.

Double check if sig gen is working by putting output lead near antenna of a working radio and tuning sig gen and radio to same frequency (600 kc).

Check resistance from pin 4 of 6Q7 to both ends of C22 (150 pF).

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 11:01 pm 
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Joined: Mar Fri 07, 2014 10:20 am
Posts: 1450
the output setting was right and when I put it next to a working radio you can here it low when you change off and on the station the radio is set at and if I have the right cap one side has 7.5 ohms and the other side has .442 m ohms


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 11:23 pm 
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Ok, connect the sig gen to the grid cap of the 6Q7 through a .1 uF cap. Set the Output Multiplier knob to 400~A.F. Can you hear the tone?

If so, move the sig gen and .1 cap to pin 4 of the 6Q7 and check there.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 11:35 pm 
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still nothing but with the generator hooked up it dull the noise in the radio even before it is turned on and also I am going to mention that this radio has a white wire like the 157 that is not connected any where


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 Post subject: Re: marconi model 160
PostPosted: Jan Mon 09, 2017 11:45 pm 
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Location: San Diego
Where is the white wire connected?

Do you have a small permanent magnet speaker? Connect the sig gen to it directly, black to one side and red to the other. Output Multiplier knob on 400~A.F. Can you hear the tone?

Matt


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