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1060 - Purchased, now restoration

Thank you i will be able to figure out which leg is the wiper now, unfortunately looking at the schematic, i am still struggling to figure out which orientation i put the pot in.

i do apologize if i am trying your patience at this stage - i appreciate your continued assistance

I am worried at the way the biasing would not stabilise at any value at all previously.
Even with the wrong pot installed, should i not have seen a stable reading of some sort?
I am conscious that if i pull the board again, should i be checking capacitors etc?
I mean i replaced all resistors and transistors - but did not touch any of the electrolytics after the magic smoke incident.

To elaborate on the attempted biasing - values would jump really really high (120mv) then start slowly drifting towards 0mv. literally no stability at all.
 
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paultlaw said:
Thank you i will be able to figure out which leg is the wiper now, unfortunately looking at the schematic, i am still struggling to figure out which orientation i put the pot in.
Click to expand...

Just look at the board. There are two holes directly across from each other with a squiggly line between and then a line or arrow coming down from a third hole. That’s the center wiper. Easy peezey.:thumbsup:
 
Bias will be extremely touchy and possibly unstable if you are using a much higher value trimmer. Best is to use a multi turn in the original value for the bias. From memory on the couple of 1060's that l have done l had to increase the value of the centre voltage trimmer to allow for greater range.
 
MBuras said:
Just look at the board. There are two holes directly across from each other with a squiggly line between and then a line or arrow coming down from a third hole. That’s the center wiper. Easy peezey.:thumbsup:
Click to expand...
Thank you, The board itself does not this symbol unfortunately, just marked simply with a circle
 
paultlaw said:
Thank you, The board itself does not this symbol unfortunately, just marked simply with a circle
Click to expand...

Two holes on top and one below arranged in a triangle. The one below is the center wiper.

The best way to look at this is with a center wiper configuration pins 1 & 3 are always bridging 2 traces and the wiper is the remaining center pin, adjusting the resistance between those two points.
 
Paul, if I were you, I would ditch the old thermistor/resistor combos at H713 & H714 and replace with either a 1N4148 or 1N4448. Those may have something to do with your instability along with the proper pot values. Do you have any resistors soldered to the back of the board? Later 1060's had a 150 ohm resistor at R729 & R730. Check out this site for another great rebuild with great photos: https://forum.polkaudio.com/discussion/180594/in-love-with-capacitor-coupled-output-sound/p2
 
No resistors on back of board here. I'll check if I have some those diodes!
Do you mean to remove the pots altogether and drop a 150ohm resistor instead?
 
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No, the 150 ohm resistors are in addition to the pots at R729 & R730 and are soldered to the back of the board. Check out the photos in the link I posted earlier. I believe it’s to get a better range for bias adjustment. Seemed to work well for me.
 
I reinstated the original pots and the new 150 ohm resistors and new diodes,could not get bias dialled in. So I removed the resistors and tried again. Worked like a charm. Set bias to 7.7 on both sides, best I could do.
Result.
 
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Tone controls and phono board next. Thanks for sticking with me folks, I appreciate all the advice and help. Truly thankful
 
Nice work! I guess the resistor isn't always applicable. :dunno: 32V may be close enough. I've read that it should be set to half of your supply voltage. You can measure that on pin J709 or J710, same thing. Have you listened to it yet or waiting to do the rest of the amp?
 
I tested it for about 20 minutes, very happy with it, sounds great, using B&O redline 60.2 speakers and some pink Floyd.
Not one for flowery words describing how things sound but sounds very smooth, and punchy too.
Phono stage next maybe, then tone section.
Might tackle power switch next actually, mike Sweeney style
 
Tone board caps replaced, no issues this board thankfully. What is the general consensus on the transistors on this board, should they be replaced as a matter of course? If I do, should they be hfe matched?
 
I don't much care for those little round transistors, some call them flying saucer types, they sometimes fail and get noisy.
Gain matching may or may not be required in this case.

According to the relevant data sheets;
2SA493 Y gain code is 120 to 240 Hfe.
2SA493 GR gain code is 200 to 400 Hfe.
2SC1000 GR gain code is 280 Hfe
2SC1000 BL gain code is 530 Hfe

If I haven't made any errors, generally speaking, on this style preamp-tone board;
H401,402, 405, 406, (NPN) can be replaced with 2SC1000 (GR or BL) or KSC1845 F gain code.
H403,404, 407, 408, (PNP) can be replaced with 2SA493 (Y or GR) or KSA992F F gain code.

Japanese transistors are usually coded as 2SA, 2SB are PNP, 2SC, 2SD are NPN
Fairchild (and now On-Semi) carried this forward in a way, KSA, KSB are PNP, KSC, KSD are NPN.

YMMV
Tom
 
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Thanks Tom, I will have a rummage and see what i have!

Updated, tone board now fully complete (had the correct transistors), so happy with the sound!
Went at the power switch, it has a kind of relay type contact, if that makes sense, I gave it a good deoxit and rub with single sheet of paper, nice and clean now, sorry mike, did not have the stones to disassemble! I will however now replace all of the loudness switches etc.
I have questions on the phono board with respect to what type of caps to use in each position, the big browns will stay though.
 
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Question - For bypass caps can i use a 0.22uf/0.47 film cap (250v) on each of the caps - the main filter (10000uf) and the coupling caps (2x 6800uf)?
 
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