President Lincoln MK1 2SC1674 replacement?

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Vapor
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President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

Hi to all and I hope some one in the know can help me with the replacement of a part in my president Lincoln mk1

From what I have read this part going bad can cause squelch chatter, the part I want to replace is 2SC1674 I can find the parts but there is a problem in which 2SC1674 to get as the replacement part? I don't want to do any mods to different parts as I have seen this some times causes more problems. all I want to do is replace the original part.

2SC1674 M 40-80
2SC1674 L 60-120
2SC1674 K 90-180

Does anyone know the correct value for the Lincoln MK1 please? will I need a M L or K part 2SC1674

thanks in advance.
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Re: President Lincoln MK1 2SC1674 replacement?

Post by ch25 »

First from the drawer. No need to go deeper.
Chris
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

ch25 wrote: 01 Nov 2018, 17:37 First from the drawer. No need to go deeper.
Chris
Why do they make 3 versions if it doesn't matter?
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Re: President Lincoln MK1 2SC1674 replacement?

Post by ch25 »

Put the same version you had.
Difference is in β, but in SQ circuit does not really matter.
Point me where this TR is located exactly? How do you know that it is defective?
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

its Q101 located next to L101 when it goes bad it causes SQ chatter, only what I have read and my Lincoln does suffer with this, I have read you can change to a 2SC1999 but again some say it works some say it doesn't, so I thought I would replace with an original 2SC1674 but before I remove it I would like to purchase new one.
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Re: President Lincoln MK1 2SC1674 replacement?

Post by ch25 »

Q101 is a RF amp. When it's go bad, your receiver is deaf. I don't think, that you need to replace it. It have nothing to do with SQ circuit which is based on NJM2902 opamp.
Does SQ chatter on dummy load or only on antenna? Does it chatter in autoSQ position, or when you set it manually too?
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

it chatters in auto SQ position and manual position.

this is what I read from internet
http://www.normsweb.com/tektips/lincoln.shtml
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Re: President Lincoln MK1 2SC1674 replacement?

Post by ch25 »

On antenna, dummload, without antenna?
On antenna it is pretty common, that any signal over threshold will open SQ. That is why I never use it except FM sometimes.
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Last edited by ch25 on 01 Nov 2018, 18:56, edited 1 time in total.
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

on the antenna, low signals chatter in and out of SQ

to the point that you either have the SQ off and hear them, or if you have it set to just on the back ground noise, it chatters in and out and even low signals do the same
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Re: President Lincoln MK1 2SC1674 replacement?

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let me describe it better, back ground noise s3 set SQ just above and this is on FM. if I get a signal of S5 it will chatter in and out, back off SQ and back ground noise floor will chatter in and out. so S3 to S5 can't open SQ with out chatter
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

it never used to be like this, set SQ so a signal of S5 would lift SQ and I would get a clean signal in, but now it will chatter the SQ
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Re: President Lincoln MK1 2SC1674 replacement?

Post by ch25 »

1. That is normal behaviour of SQ circuit.
2. Lincoln have wrong designed FM demodulator. That can be easily fixed.

Remove 10k resistor as marked on the pic.
remove.jpg
Take 5.6k and place as marked on another image.
new one.jpg
Voila. Difference in FM will be huge.
Also it is good to replace C412 from 47nF to 10nF - Opens deemephasis, better and louder FM reception.
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

so you remove the 10k resistor and don't replace it, then place a 5k to 6k resistor and place it in the place highlighted in pic 2

that looks easy enough, thanks

think that's a 5.6k resistor, what W value should it be? 1w 2w 1/4w 1/2w
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Re: President Lincoln MK1 2SC1674 replacement?

Post by ch25 »

5.6 kΩ :) Small one. Wattage is not important here.
You can use even 1kΩ, in that case low signals will pass better.
After, check and realign L115 for maximum signal. Plastic screwdriver! Just find on the air fair low FM station and tune L115 for maximum signal. Simple as that.
C401 is located on vertical PCB next to that resistor you will be removing. In case you want to replace it too.

Also it is good to replace C61 from 560pF to 47pF, TX audio will gain high tones, become less muddy.
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Re: President Lincoln MK1 2SC1674 replacement?

Post by Vapor »

Thanks very much, will give it a go.
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