So just got around to Re-Capping My NAD 3020i Amplifier which I've had for around 3 years, It's never given me any problems and this is the first time I've had the hood off.
The first thing I noticed was that it's fitted with ST Microelectronics output transistors MJ2955 and MJ3055, the codes on the transistors are 99045, 99051,and 99044, I've tried to see if I can get a date for these codes but so far drawn a blank.
Something is telling me they just don't look original, The other NAD's I've worked on have all had Motorola transistors fitted.
Anyway, I was wondering if this would be a good candidate for fitting the 0.33R Emitter Resistors and the 4R7 Base Stopper Resistors.
Would appreciate other members Thoughts.
The first thing I noticed was that it's fitted with ST Microelectronics output transistors MJ2955 and MJ3055, the codes on the transistors are 99045, 99051,and 99044, I've tried to see if I can get a date for these codes but so far drawn a blank.
Something is telling me they just don't look original, The other NAD's I've worked on have all had Motorola transistors fitted.
Anyway, I was wondering if this would be a good candidate for fitting the 0.33R Emitter Resistors and the 4R7 Base Stopper Resistors.
Would appreciate other members Thoughts.
Looks like a yyddd format date code, so the amp would seem to have been on the bench about a decade into its life.
Despite the somewhat problematic construction, these units aren't failing left and right either, so you'll have to weigh the risks of that vs. accidental misimprovement.
I'd always tend towards the lowest emitter resistor value you can still get away with, which generally is 0.22 ohms. It's always a tradeoff between stability and distortion performance.
Despite the somewhat problematic construction, these units aren't failing left and right either, so you'll have to weigh the risks of that vs. accidental misimprovement.
I'd always tend towards the lowest emitter resistor value you can still get away with, which generally is 0.22 ohms. It's always a tradeoff between stability and distortion performance.
Thanks for the reply I was sort of thinking the same thing, "If it 'aint broke, Don't fix it.
What I forgot to mention in the original post is that when I removed the transistors to get rid of the copious amount of thermal paste, I found one of the output transistors had 3 Mica Washers under it and another had 2, That's what really made me wonder if the transistors had been replaced (Badly) at some point.
I have a 3020 and a 3130 winging their way to me, both with blown O/P stages, So will be fitting the MJ15015 / 16 combo or similar, and I'm guessing from reading the other posts regarding replacement, these will require the mod.
Still need to do a little more reading / research, but it seems that the BD139 and BD140 are a suitable replacement for the drivers.
What I forgot to mention in the original post is that when I removed the transistors to get rid of the copious amount of thermal paste, I found one of the output transistors had 3 Mica Washers under it and another had 2, That's what really made me wonder if the transistors had been replaced (Badly) at some point.
I have a 3020 and a 3130 winging their way to me, both with blown O/P stages, So will be fitting the MJ15015 / 16 combo or similar, and I'm guessing from reading the other posts regarding replacement, these will require the mod.
Still need to do a little more reading / research, but it seems that the BD139 and BD140 are a suitable replacement for the drivers.
From what I remember original 3055,s had a slightly different die structure ,more rounded and domed with a thinner clamping base .
I am going back to around their introduction , modern versions have the standard modern die structure .
This was a help to date any amps I repaired , JLH,s original class A design used the early versions.
I also came across them in an early stabilized power supply .
I am going back to around their introduction , modern versions have the standard modern die structure .
This was a help to date any amps I repaired , JLH,s original class A design used the early versions.
I also came across them in an early stabilized power supply .