Marantz Model 18

[tonebells]

The only one it had was around 250k.

Tony

 

[tonebells]

400Hz at MPX matrix output to selector switch.

Tony

 

[tonebells]

At the gate of Q603 & Q604

Tony

 

[tonebells]

The distortion shows up after the junction of R626, R628 and C620.

Tony

 

[tonebells]

FM mute works much better now the the trimmer R328 is installed.



Tony

 

[tonebells]

Voltage at Q605 is off

• d is -11.8 should be -12
• g is -3.8 should be 0
• s is -4.9 should be -1.4

Tony

 

[tonebells]

Does any know a good sub for 34-1012 fet in the MPX matrix board.

Tony

 

[tonebells]

I swapped the fets Q605/606 and the issue moved to the left channel.

 

[txturbo]

Nice!

Do you have a way to measure the good FET?

 

[tonebells]

I am not sure what that would take. I have a Super Cricket.

Tony

 

[txturbo]

Were you able to establish a cross for the JFET? If not I may be able to pull a working example out of an 18 and test it.

 

[tonebells]

Tom suggested 2N5460,61 or 62. All I could find was 2N5460. When I get the old ones out I could send you the one that is working.

Tony

 

[tonebells]

Replaced Q605/Q606 with new 2N5460s and the FM sounds good. txturbo let me know if you want the old ones.



Tony

 

[txturbo]

Nice work!

 

[tonebells]

Nice work!

Thanks txturbo. I would not be able to make it through these repairs without the help of you and the other great people on Audiokarma. Thanks again for all the support.

Tony

 

[tonebells]

I was just looking at something and realized there are two different ways to wire the mute adjustment.






Tony

 

[tonebells]

Amps before.



After





Tony

 

[tonebells]

I replaced the speaker relays(R48-5D5-6L). I think I can finally call this one done.

Tony