Marantz 18 transformer
- Thread starter calman46
- Start date
I'm not following you here Tom, Do you have the info to make the separate scope transformer?
I am installing another transformer in a recapped 18. The original transformer was ruined by a so called rewinder.
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I installed the donor power transformer and AKer RV59's stand alone scope transformer and all went well . A big thank you to RV59 for all his help and a real nice job on his design and directions . My 18 is playing, both channels , scope is working but I have no bias on the left, I get no reading across R28 (0.47ohm5W) or R35. I tested the trim pot and its tracking ok, I lifted the emitter resistors and I got 0.7 ohm &0.9 ohm . . I'm using MJ21193/94 outputs transistors . I tried matching voltages with the other channel (I have 61mV on the right across both emitter resistors ) I didn't find any other discrepancies . I'm cleaning the trim pots again . Any suggestions ?
I took out the trim pot clean it, tested it , lifted and diode checked Q1, and CR17 both passed . No way out voltage measurements and the channel is working. I'm getting DC readings now(across the emitter resistors) on the troubled side ,they're are erratic, any where from 17mV to 60mv .I can adjust the bias with the trim pot up or down but it doesn't settle down. Any ideas?
RV59
Active Member
Glad to help.
And happy to contribute to the perenniality of these formidable receivers.
I did have the same problem with the bias one year ago, trim pot was the culprit.
I don't understand where your problem come from...
I might have found the problem. The Emitter of Q1 is soldered to the case of the trim pot for the wiper connection (by design) . I think it needs a good hot solder joint , I think I got one this time. The channel has previous repair work and there was a big glob of solder on the trim pot . I've been testing it and so far its working with a little tweaking of the trim pot each time .
I'm still chasing this amp Bias adjustment. I swapped the trim pot with one from my donor unit and have the same results . The bias will be good and stable then drop off to 0mV then come back and fluctuate up and down, sometimes its goes to zero sometimes to 80mV it doesn't seem to effect the output of the channel (headphones) ??????
Widzew83rts
Member
i need to replace R36 i my another marantz 18 ,do you know where can i faind replacment?
Widzew83rts
Member
yes but can you send a link exacly becouse there it ton of them , i dont have expierence and possibly i will buy wrong one
Only four that are five watts. https://www.mouser.com/Passive-Comp...g9nZ1yzvvqx?P=1z0wui7&Keyword=.47+ohm&FS=True
Tony
Tony
Widzew83rts
Member
in my marantz right channel sound not clear . I measured all right channel and its looks good exept R36 its reststance 2 ( its should be 0,47). And when i do Bias adjustment to 80mv it goes down slowly , it doesnt keep 80mv
