Marantz Model 18

calman46

calman46

AK Subscriber
Subscriber
We need a list . I want to try subs for Q7&Q10 and Q8 &Q9 .(Q7 &Q10 are not listed in parts list ?? 34-1003) I want to see if replacements will help make the amps boards stabilize quicker . The amps go to about 100mV on start up and start to fall ,replacing Cr17,18 helped but one side is a lot slower to come down than the other. What I know is the PNP type was replaced with a HEP 5006 which is CBO 80v, CEB 80v, EBO 5v, Ic 4A, 2MHz, hfe 60@1.5A. I have some MJE15033g/ MJE1532g but they would be so overkill ,I'm not sure if they would work. Any suggestions , thanks
 
Register to hide this ad
I used On Semi (PNP) 2N5195 for Q7/Q10 and On Semi (NPN) 2N5192 for Q8/Q9. Work fine.
 
Installed new OnSemi@ Q7-Q10 , bias is better but trimpot is almost full CW to get 77mV ,I can get 80mV put it won't stay . I looked for a good fit replacement trimpot but no luck so far. I don't think there is anything wrong with them .
 
I have my 18 running at 60mV bias +/- 2mV. I have replaced Q7-Q10, the output transistors are MJ21193/94 also CR17/18 have been replaced with 3 1N4148 diodes in series . I need the trimpots full on to 80mV and it gets erratic .The pots seem to work fine at the lower voltage setting . Any problems with running at the lower bias ? The orignal 80mV bias was spec for the orignal transistors . Any thoughts ?
 
My 18 has had a lot of repairs in the past. Lots of parts in the output are not original. One channel adjust to about .06v the other about .05v. It looks like it will take a bit of work to get to right.

Tony
 
That's is how my 18's bias is .06v (60mV). I'm thinking maybe because of the mixture of old and new parts . I was listening to the FM with cheap headphones and it sounded great , I was surprise especially with the cheap headphones. Glad to see you got your scope working .
 
Looks like the trim pots were the biggest problem there. I will try to get the FM sorted next.

Tony
 
I had my trimpots out and the tracked fine but I suppose they could still fail in circuit .I believe they are wire wounded . My 18 went to 80mV before I replaced Q7-Q10 . I was going to mount some through the hole trimpots I have on PCB board but with all the connections it was messy .
 
I have my 18 back together and playing but I notice the FM muting HI/LO filters and Hi blend switch are not working . The FM muting light mounted on the board on back does light right before the push button click locks then goes out.Should this light be on all the time when the FM muting is on ? It does not seem like the other 3 switches are working . I'm going for a good cleaning . I want to take a look inside the switches .
 
did the muting ever work. Mine was missing the trim pot R328 to adjust the muting. Once I added it it works fine. The light should be on when no station is tuned. look at page three of the service manual. Make note on the (*).
 
I have the switches a good Deoxit bath . I see in SM where to adjust it . So the FM muting light will go on when no station is tune , I didn't see that in my SM. When I had the push button in I still had all the between station noise . I'll check it out................. I'm not sure if the FM muting ever worked
 
Back to bias problem, what is the voltage drop of the old CR17/18 compared to the new series 1N4148s, diode check with a DMM might work. If voltage drop with the new 1N4148s is lower there's your problem. The base of Q1/2 is too positive. The trimmer adjusts the conduction of Q1/2, the more Q1/2 conduct the colder the bias. Also the new transistors could have slightly different turn on voltages and all of this is adding up.

Craig
 
Its in the owners manual ,I got it. Tonebells Thanks

Ilwhtt >>>>I could still adjust it to 80mV when I changed the diodes but the bias was unstable .When replaced Q7-Q10 I couldn't get 80mV but the bias settled down. see post #4
 
All set here , the FM muting is working . This 18 sounds great through a pair of Wharfedale Harewood speakers (2-way). I have some better speakers to try this 18 out on but it sounds pretty dam good . Scope looks good also .
 
i was wondering if its normal or not, when i turn on reciever and tryig to set up station there is no stereo light , but when i turn of reciever and turn it on the stereo light is on also when i turn on muting on everythig works fine
 
Hi.
Can you help to faind Q2 and Q6 in the store i faund them but there is lots of differend , can you send me a lint so i czn buy them?
 
I haven't been playing this 18 too much and had noticed that one channel was slower to come on than the other. I finally open it up and one of the replaced filter caps had vented. I don't see anything burnt. I hope it's not the transformer. I going to take out both filter caps and check the transformer voltages going to the caps. Any suggestions?
 
You must log in or register to reply here.
Back
Top Bottom