Got a reprieve so still here 😀
Correct transistor turned up today and fitted. Soldered the resistors I already had to the emitters - cut the traces - and fired it up. Thermistor wires shorted - headphones - safety lamp...
We have sound!! 😱
Switched it off as not set bias yet but that's a good start in my book!!
Many thanks for the support - it's always good to feel there's someone there to help in case it all goes horribly wrong!
Correct transistor turned up today and fitted. Soldered the resistors I already had to the emitters - cut the traces - and fired it up. Thermistor wires shorted - headphones - safety lamp...
We have sound!! 😱
Switched it off as not set bias yet but that's a good start in my book!!
Many thanks for the support - it's always good to feel there's someone there to help in case it all goes horribly wrong!
That is good news 🙂
Set the bias carefully and always err on the low side with a design like this. In practice any audible distortion from having zero bias will vanish at even a few milliamps.
Set the bias carefully and always err on the low side with a design like this. In practice any audible distortion from having zero bias will vanish at even a few milliamps.
Set 'centre voltage' and 'idling current' as per service manual instructions - screwed back together - attached speakers - have audio and no smoke! 🙂
How long will this last? Who knows but I'm ticking it off the 'things to fix' list for now.
Just need to find some some vintage speakers at the skip now...
Any speaker recommendations for this particular amp?
How long will this last? Who knows but I'm ticking it off the 'things to fix' list for now.
Just need to find some some vintage speakers at the skip now...
Any speaker recommendations for this particular amp?
New or used? If new, the Q-acoustic 3020's aren't bad with NAD 3020 type amplifiers (hows that for matching titles? 😀) and they're great value for money. Used speakers are often a lucky dip of type, availability, condition and the seller's preparedness to pack and ship them. You may have to take what comes in your location.
Well done with the amp 
Not sure what to suggest with the speakers, it really is a case of what you can find.
Not sure what to suggest with the speakers, it really is a case of what you can find.
Probably used - to keep it period! 😀 I have a set of Mission 760iSE somewhere from around the same time. A bit bright from what I remember...
Righty then...
Had the amp playing for a few days and seems well except for a dodgy volume pot. If it sounds 'OK' should I bother changing anything else while I'm at it?
It does run hotter than other amps I've had - not smelling of burning hot or anything - will keep an eye on it.
Talking of other amps! Dug out my very first amp - a Sony TA-313. Cool amp with big meters and SPRING REVERB on the Mic input. Karaoke time!! 😀 Quick clean of the pots and it sounds as good as ever!
Had the amp playing for a few days and seems well except for a dodgy volume pot. If it sounds 'OK' should I bother changing anything else while I'm at it?
It does run hotter than other amps I've had - not smelling of burning hot or anything - will keep an eye on it.
Talking of other amps! Dug out my very first amp - a Sony TA-313. Cool amp with big meters and SPRING REVERB on the Mic input. Karaoke time!! 😀 Quick clean of the pots and it sounds as good as ever!
If it is drawing the correct bias current at all times (meaning that the bias hasn't crept up when/after playing loud) then any heat is going to be normal and a limitation of the finite smallish heatsinks.
Old electrolytic caps and checking for poor soldering would be the number one preventative maintenance on the NAD... and the Sony too.
I remember the Sony gear of that era, you just don't see that kind of thing nowadays. I think from memory that one used a hybrid thick film output module (aka a forerunner of the ubiquitous STK type modules).
Old electrolytic caps and checking for poor soldering would be the number one preventative maintenance on the NAD... and the Sony too.
I remember the Sony gear of that era, you just don't see that kind of thing nowadays. I think from memory that one used a hybrid thick film output module (aka a forerunner of the ubiquitous STK type modules).
With the original MJ2955/2N3055 transistors or with the replacement MJ15003/04's? Did you adjust the idle current according to the specs given by the manufacturer?
Best regards!
I set recommended voltage from the service manual using the MJ15003/04 not MJ2955/2N3055. You think they should be different?
Took a while to figure out what jumper they meant - it was the biggest blobs of solder on board!
Took a while to figure out what jumper they meant - it was the biggest blobs of solder on board!
Also - rescued a NAD 501 CD player in the skip the other day - matches the amp perfectly and is fully functional but not idea if it's worth keeping...
You must have some good skips near you 😀
My criteria for stuff like the CD player would probably be whether or not it was in good cosmetic condition. If so then all things are possible 🙂
My criteria for stuff like the CD player would probably be whether or not it was in good cosmetic condition. If so then all things are possible 🙂
Very understanding skip attendants here. It never ceases to amaze me what people throw away. Snagged a vacuuming robot thingy last week - mint condition! Not something I'm likely to use but I'll either scavenge parts from it or pass it on to someone. There's loads of Dysons - super easy to recondition, (cheap) hifi's galore, hundreds of bikes (not sure if they get recycled but hope so), and general useful stuff that other people would be VERY grateful for.
I digress - CD is in V.Good condition - will donate to someone who will use it...
I digress - CD is in V.Good condition - will donate to someone who will use it...
Well - I didn't get the matching name but did get Q Acoustics 2050i. Couldn't say no - as new - £100. Can always punt them on at that price if I don't like them.
So - back to the amp...
Should I also add base resistors before really using this amp in anger?
With something like the NAD I would probably say that if aint broke then don't try and fix it.
If it is all still working OK and the bias is reasonably stable then I would just use and enjoy. Without detailed testing you can't really say whether they do any good or not.
If it is all still working OK and the bias is reasonably stable then I would just use and enjoy. Without detailed testing you can't really say whether they do any good or not.
Just saw this thread... back in the day there were limited replacements for the 3055, So the MJ15003/4 were usually recommended. I preferred the 2sd424/2sb554 because they had much better gain and cob characteristics.
The 3055/15003 had similar gain, but in demanding loads, the 2sd424 would put less stress on drivers, increasing reliability. For me the important parameter was cob. At 1000pf, the MJ15003/4's put a lot of frequency dependent stress on drivers, to the extend that they had a sonic character. I do not find published cob numbers for the 3055, but given the die size, I would think its closer to 200pf. The 2sd424's 300pf is much closer.
The 424 later morphed into the much loved 2sc3281... having said that, the 15003/4's are very reliable workhorses and sound great when the design is done with their characteristics kept in mind...
The 3055/15003 had similar gain, but in demanding loads, the 2sd424 would put less stress on drivers, increasing reliability. For me the important parameter was cob. At 1000pf, the MJ15003/4's put a lot of frequency dependent stress on drivers, to the extend that they had a sonic character. I do not find published cob numbers for the 3055, but given the die size, I would think its closer to 200pf. The 2sd424's 300pf is much closer.
The 424 later morphed into the much loved 2sc3281... having said that, the 15003/4's are very reliable workhorses and sound great when the design is done with their characteristics kept in mind...
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