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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 7:52 pm 
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found the problem the wire I thought was a ground was one of the output transformer wire and the other was attached on the other side by itself and I hooked on the two output trans wires and the speaker seems fine on the highest volume with no distortation but I found the distortation problem it is when you turn the tone all the way up


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 8:13 pm 
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Location: San Diego
Ok, so is there any difference in distortion comparing the original speaker with the permanent magnet speaker? Or do they both sound fine until you max out the tone control?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 8:15 pm 
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they both seem fine until you max out tone


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 8:37 pm 
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Ok, try inserting an 18k resistor between C26 and the tone control.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 8:59 pm 
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Location: Powell River BC Canada
spsquires wrote:
found the problem the wire I thought was a ground was one of the output transformer wire and the other was attached on the other side by itself and I hooked on the two output trans wires and the speaker seems fine on the highest volume with no distortation but I found the distortation problem it is when you turn the tone all the way up


When it is playing with no distortion, what is the voltage on pins 3 and 4 of the 6F6 tubes?

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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 9:02 pm 
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I tried the resistor and I can turn the tone all the way up when you go above half on the volume it has really bad distortion


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 9:10 pm 
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And when the tone control is not maxed out, there is no distortion?

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 9:16 pm 
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yes when the tone is not maxed out there is no distortation but it also seem the tone has some control over the volume has it changes the level of volume so much


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 9:22 pm 
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Yes, I don't think it is the best tone circuit design. You can increase the 18k resistor to 47k or even 100k and it should fix the distortion, although the tone control range will be somewhat less. Also, double check the value of R10 (250k). You can measure it without disconnecting it.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 10:11 pm 
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so should I put another resistor in and try and which pins is r-10 connected to thanks


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 10:24 pm 
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It is up to you whether to increase the 18k resistor. It is a tradeoff. It will eliminate distortion at the cost of somewhat decreasing the tone control range.

To figure out where R10 is connected, check the schematic and use your highlighter! Look up tubes on nj7p.org if you need to know the pin numbers.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 10:34 pm 
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so am I right to say one end connects to pin 3 of 6q7 if so it is .583 m ohms


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 10:59 pm 
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also to the question about tube 6f6 voltage with no distortion pins3 have 277dcv and pins 4 have 301dcv


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 11:16 pm 
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Yes it does connect to the 6Q7 plate, and 583k is way too high. Needs to be replaced.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 11:24 pm 
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will it be ok to use a 68k and a 180k in series and I just looked at the resistor bands and it has a red yellow red and green


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 11:35 pm 
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Yes, 68k and 180k in series will work great. Or 270k would be close enough if you have one.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 11:43 pm 
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That's one way but you can go to the preferred range either side I would go 270K, That resistor is a common failure, as are those on the grid of the OP tube. One fail says they were not checked properly when it was "repaired". This is why I advocate checking them as the caps are changed, you virtually eliminate the double work finding & replacing them later, after they cause problems, as now. That resistors failure, can and usually does, cause low volume and distortion.

I still stand by my previous statement re the competency of the one you got to mess this set up.

Marc

Addendum: Two of us are on the same page.


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 Post subject: Re: marconi model 160
PostPosted: Jan Thu 12, 2017 11:49 pm 
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I put the new resistor in and it has half or less the volume and is cutting in and out but in my other comment about the bands the resistor was twice what I installed and the one I took out looked original solder


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 Post subject: Re: marconi model 160
PostPosted: Jan Fri 13, 2017 12:16 am 
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Check resistance of all resistors in the 6Q7 and 6F6 circuits. Check wiring connections against schematic. Measure voltages.

Matt


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 Post subject: Re: marconi model 160
PostPosted: Jan Fri 13, 2017 12:37 am 
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would you like the voltage posted if so I will do in the morning thanks


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