Which are OBSOLETE and UNAVAILABLE, at least of Mouser is concerned (maybe you trust EBay?)
is a nice fantasy but then availability punches you in the nose.
11015/6 listed as active at Digikey, but only one of the pair was in stock. Might not be for a long time considering that it’s hard enough to get high volume parts. I may still have a pair or two from when ST use to make them, and a couple of the lower voltage 11014’s. Got old non-audio equipment I can salvage a few out of if I get desperate.
I dont trust Ebay at all
It likely depends on region.
I only listed those options because they are what is available at mouser
in my region
On Semi and Central Semi
cover the range of those types.
Some NPN have limited stock, but they are in stock.
Others range from 400 to 2000 units in stock.
Either way, it is a relative straight forward repair.
And T03 Darlingtons are still easy to get
Far as I understand the " G" suffix is for PB free
So might help to add a G suffix to whatever your
searching for. Since most newer manufacturing
will meet PB free standards
If you search without the G, the G (and NOPB, and PBFREE) part numbers do come up. You also get the JAN parts from Microsemi that start around $60 each (not a typo or exaggeration).
Thanks everyone, a lot of useful informations !
That's what I thought I understood, I see your name popup a lot on gear related forums, and you seems to have a fair bit of experience !
I started with tubes like you, and never looked back to SS. But it has always been a frustration not to (taking the time to) understand SS power amps, time to make a change !
I'll check Crate and H&K, seems to be a good start indeed. My first amp was a H&K Tour Reverb, I always liked it !
My only experience with SS power amp was the 60-100W Hi-Fi Power Amplifier by Rod Elliott.
Should I replace them by default ? I tested them for shorts, there was none. Can it be defect without being shorted ?
ONSEMI MJ11015/6 are in stock at Mouser, RS and Farnell. I'll try it, thanks again for your help !
That's what I thought I understood, I see your name popup a lot on gear related forums, and you seems to have a fair bit of experience !
I started with tubes like you, and never looked back to SS. But it has always been a frustration not to (taking the time to) understand SS power amps, time to make a change !
I'll check Crate and H&K, seems to be a good start indeed. My first amp was a H&K Tour Reverb, I always liked it !
My only experience with SS power amp was the 60-100W Hi-Fi Power Amplifier by Rod Elliott.
Should I replace them by default ? I tested them for shorts, there was none. Can it be defect without being shorted ?
ONSEMI MJ11015/6 are in stock at Mouser, RS and Farnell. I'll try it, thanks again for your help !
Don't forget, R1 & R2 within the transistors will be missing. Might not be an issue but you will find out later.
Any transistor all the way back to T5 can get fried if you lose the output stage. If they don’t you can still use the original parts. They either work or they don’t. The bias regulator T6 is the only critical one - if it is open and you put in new output transistors - bang, as soon as you plug it in. That’s why you use a dim bulb, so it doesn’t go bang (Just draw current and light the bulb). If shorted you just get a lot of distortion. I will generally change it if there has been any collateral damage (torched resistors). No other failure mode will result in excessive output stage current (ie, bang). DC to the speaker, maybe. Clipping half the waveform off, maybe. But never fire one up with a speaker connected until you’ve ironed out all the bugs. Connect the speaker thru a 1k resistor initially - so you can test up to full clipping without blowing anything or annoying the neighbors. You should be able to crank it all the way on a dim bulb, then without. Only then connect a speaker directly.
Make sure the current limit transistors (and the diodes in the collector) haven’t failed open either. The amp will work without them - until you short the speaker output to ground (then, bang of course). If you have an hFE tester or function on the DMM use it. Or the diode test from base to emitter - it should act as a diode. Then short collector to base, and the Vbe reading should drop. If it doesn’t drop the transistor is suspect (meaning the gain is very low or zero).
Make sure the current limit transistors (and the diodes in the collector) haven’t failed open either. The amp will work without them - until you short the speaker output to ground (then, bang of course). If you have an hFE tester or function on the DMM use it. Or the diode test from base to emitter - it should act as a diode. Then short collector to base, and the Vbe reading should drop. If it doesn’t drop the transistor is suspect (meaning the gain is very low or zero).
So, I replaced output transistors with MJ11015/6, tested with light bulb limiter and it seems to work.
I have sound, not a lot of volume though, might be because of the light bulb limiter ?
Attached, the voltages WITH light bulb limiter and a 8 ohms speaker connected.
It seems to be an imbalance in the bias circuit, or is it normal ?
What can I check next before trying without the limiter ?
I have sound, not a lot of volume though, might be because of the light bulb limiter ?
Attached, the voltages WITH light bulb limiter and a 8 ohms speaker connected.
It seems to be an imbalance in the bias circuit, or is it normal ?
What can I check next before trying without the limiter ?
“Not a lot of volume” but other than that normal sound suggests that signal might somehow be attenuated before getting into the power amp stages or that the gain is less than it should be. Is T11 ok? Try removing. Also make sure feedback is working - make sure C85 isn’t dried out as that will reduce gain and usually kill all the bass. The light bulb limiter will only affect maximum power, not the amplifier’s gain.
That apparent “bias imbalance” is the result of the 35.5 mv DC offset flowing through the load (Or feedback network). Perfectly normal and ok.
That apparent “bias imbalance” is the result of the 35.5 mv DC offset flowing through the load (Or feedback network). Perfectly normal and ok.
I will probe signal before and after R167, it should give an idea.
Lead channel is much quieter than clean/crunch, I have to check the preamp too.
Also, the amp seems to have been exposed to moisture, and potentiometers need to be cleaned, it could be the cause of low volume.
Good to know. I'll replace it anyway, it doesn't cost much and the PCB is already out. I hesitate to do a full elco recap.
Again, thanks all for your help, I'm relatively new to this forum and I'm thrilled by the overall experience !
Most of the time the little electro’s don’t go bad - but they do just often enough to be annoying. Low gain and/or no bass? C85. Early or asymmetrical clipping? C84, C86. Quality on these caps matters - not because of some magical subjective sound qualities, but because the ”good” ones will still be good in 25 years and you won’t have to eff with them. Long life 105C (will not be the smallest possible for a given C-V) Nichicon or Panasonic.