Discussion in 'Yamaha' started by Bratwurst7s, Jan 17, 2018.
Don't want to hijack your thread Bratwurst7s but it is strange how life goes as we have been talking so much about your M-70 and the other day l picked up it's little brother, M-50 and C-50 combo. It has even had the AC cap on the p/supply replaced.
Hope all is going well for you this week .
Hey man, no, you aren't hijacking, far from it. I think that it's great that you got that combo. The C-50/M-50 were my first Yamaha(s). I bought them in '83 at Clark Air Base in the Philippines and used them for many years. A really sweet "little" amp/pre. Enjoy them.
Thanks for the good wishes. I should be home by Friday, should be no big deal. The Doc said that the cut for the OP is only 5 to 6 cm long.
I got a little sidetracked this week with some fun speaker projects but will be back on track shortly. My Bdent order left Frankfurt on the 3rd so I'm guessing that it is at Customs here in Munich now. They aren't exactly fast at Customs, it could be a week or more before I get notice that I can pick it up.
Best wishes for the OP!
Sounds like you'll get out about in time for some nice deliveries.
Oh really, that is great to know you enjoyed them for many years. Thanks l will, haven't had a chance to give them the once over yet. I have some NS-200M's here that l would like to pair them with.
Here's to a speedy recovery .
Yeah speakers can be fun, hopefully the M-70 parts arrive soon then.
I just got back from my pre-appointment, the OP was moved up to tomorrow. I'll be back here in a few days. Thanks for the good thoughts guys.
I got back from the hospital yesterday, moving slow but moving. Tracking shows that my Bdent parts are at Customs, no news about my DigiKey order. I should be getting back in gear on this project in a few days.
The DK order is 4ea 2SC3858/2SA1494, 10ea NJW0281G/0302G, and 100ea of FJR flame proof resistors in 10 and 22 ohms. I probably should have bought more on the Sankens but the order was already over €100 as is. I'm hoping that I don't need to use any of these right now and they can go straight in my bench stock as reserves.
One thing that I haven't addressed at all is lamps. I can buy a set of 5 on ebay for ca €10 with shipping but am more inclined to replace the incandescence bulbs with LEDs but I'll look into that a little later. I also have to decide in speaker terminals, there's no way that the stock things will be staying in the amp. But again, that's something that I'll look into after I see about getting the darn thing working.
So finally getting back to potential transistor subs:
2SC1983: TIP112FS-ND or KSD1273Q or MJE15032G.
2SC1775: KSC3503DS or KSC1845FTA.
2SA872: KSA1381ESTU of KSA992FBU.
2SA914: KSA1381ESTU or KSA1142.
2SC1953: KSC3503DS or KSC2690AYS.
2SC1213A: KSC3503DS or KSC1008C.
For trim pots...
PSU control board:
VR601: 5Kohms, side adj, 5x5mm leads = Bourns 3339W-1-502LF 4-turn.
VR602: 5kohms, top adj, 5x10mm leads = Bourns 3339H-1-502LF 4-turns.
VR500, 501: 1kohms, top adj, 5x10mm leads = Bourns 3339H-1-102LF 4-turn.
or = Bourns 3296Y-1-102LF 20 turn.
Main amp board:
VR101, 102, 103, 104: 500ohms, top adj, 5x10mm leads = Bourns 3339H 1 501LF 4-turn.
or = Bourns 3309P-1-501 single turn.
VR901, 902: 100ohms, side adj, 5x5mm leads = Bourns PV12T101A01B00 4-turn.
or = Bourns 3339S-1-101LF 4-turn.
I'm going to order some of each variation and choose later. There will be some lead bending involved but that shouldn't be a big problem.
I need to make some choices concerning resistors and will be making another Mouser order tomorrow. That should give me nearly every possible part on hand. I just might start actually working on this thing in the next day or 2. On Wednesday I go to the Doctors and have my stitches pulled. I'll be glad when I've reached that milestone.
Yesterday I made a huge order with Mouser, over €500. It included parts for several projects including this one and some bench stock. Lots of metal film and MOX resistors, a couple of 15 amp bridge rectifiers and lots of other stuff. It should be here by Friday or so.
Tomorrow I'll be pulling the PSU control section and start working.
Good call, yes the speaker terminals are about the only thing l don't like about this series.
I spent some time today looking at what Hifi Collective has for binding posts, I'll probably post some of the possibilities soon and ask for thoughts. On the other hand I just got a package today with an original/good condition/used speaker terminal blocks for an AX-750. Holding them up to the back of my amp I see that they could be used. But I think that I'll go with something nicer/better.
My Bdent order arrived today. I had to pay €25 but at least I didn't have to go all the way out to Customs, always a minimum 3 hour journey. The good news is the 2SA1186/2SC2873 are P and Y class respectively so they meet the minimum specs to use, although I don't know if it would be a problem to use 2 different hFe classes together.
Rant mode ON: I suppose that DigiKey is better if one lives in the US but I'm getting to the point where I really don't like to order from them. First, they don't accept PayPal and I don't carry a credit card so I have to pre-pay my orders and I have to wait for them to email an invoice and PO# before I can make a bank draft. Second, it took a week for them to do that this time around. So I was finally able to pay for my order this last Tuesday. Now I have to wait for them to decide that they were paid. Once the order finally ships UPS usually delivers in 3 days. Compared to Mouser that's not very fast service and DigiKey has now become one of my choices of last resort. Rant mode OFF.
You still can try to match them as close as possible by using the hFE (Beta) meter. The ranks are 70 ~ 140 (P) and 90 ~ 180 (Y), not a huge gap. Hoping that the average hFE number between the ranks make it easy, but I don't believe the outputs need to be as closed tight as the differential input transistors have to.
I hope that my little parts tester will be able to reliably give me useful figures, considering some of the discussion earlier in the thread. For sure the numbers that it gave me for the 2SA1106/2SC2581 were all over the place, from a low of 54 to a high of 88. In any case at least I have some known original quality parts to work with. I'll be testing them in the near future and will post the results.
I got shipment notice from DigiKey a few hours ago.
The small transistor tester won't give particularly useful hFE information for output transistors, since it's a curve proportional to current (not a fixed number) and the tester isn't testing at a realistic current for power transistors. I wouldn't worry - there's no real need to match PNP/NPN since they almost always have different curves anyway.
It is good to match parallel (same-gender) transistors though. If you're lucky they'll be from the same batch. You'd need a lot of extra transistors (and a curve tracer, or a DIY higher-current testing setup) if you wanted to match them. You could use the small tester just as a best-possible-effort to decide on same-gender sets for L/R sides of the amp though.
Well I tested the new drivers today. Results (hFE):
2SA1837 / 2SC4793
1: 164 / 149
2: 159 / 147
3: 158 / 148
4: 154 * / 150
5: 159 / 147
6: 164 / 152 *
7: 164 / 147
8: 155 * / 153 *
9: 159 / 147
10: 158 / 150
* denotes the ones that I chose to use.
And just for grins and giggles I went ahead and tested the outputs:
2SA1186 / 2SC2837
1: 94 / 112
2: 103 / 111
3: 144 / 127
4: 94 / 114
5: 131 / 111
6: 135 / 129
7: 51 / 106
8: 92 / 103
Fwiw I ran the test on each of the 5 times and the little fellow gave the exact same results each time.
I carefully removed the psu control board assy today. Whoever was in here before me just cut the power cord wires for access and then tack-soldered them back in place. Sloppy work. When I get ready to install the assy I'll pull the cord + strain relief and feed 10cm or so extra wire into the case. Then I can clean up the mess on the posts and wrap the wire around it for a good mechanical connection before re-soldering.
I think that it will be best to de-solder the wire blocks from the trafo/power switch and then de-solder the boards from each other. Then I can start testing all of the components, replace the caps and anything that turns out bad etc. Actually, my Mouser order arrived today so I now have enough metal film resistors that any carbon film resistor that gets removed for testing will be replaced with MF regardless. I also have replacement metal film and MOX resistors for the entire amp if it comes to that.
There are some more spots where someone has been soldering, next step is to map them out.
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