Just a little help only. You change the other channel as well.
I'm happy that you enjoy your amp again!
I'm happy that you enjoy your amp again!
More than little!
Can I ask your background, you seem very precise and clever and how long you been an electronic engineer. You dont have to answer I'm just curious 🙂
Can I ask your background, you seem very precise and clever and how long you been an electronic engineer. You dont have to answer I'm just curious 🙂
I'm not an electronic engineer, I study low level electronic diploma after high school, after that being an electronic components salesman for many years.
In normal time I reading all things about diy amps, commercial amp schematics and I will build some amps to test among those amps seems to be good.
In normal time I reading all things about diy amps, commercial amp schematics and I will build some amps to test among those amps seems to be good.
Well than, who can imagine what would be if you have finished engineer degree 😉
Very good conclusion. Strange transistor failure, hard to detect.
Some people really know their stuff!
Exactly! He didnt even have the amp just numbers and schematic!
Exactly! He didnt even have the amp just numbers and schematic!
Actually I'm stupid so that I cannot go to the U after high school, so that I don't know those difficult theories in transistors and amplifier.
I just interested in reading all kinds of amplifier schematics and build many testing amps, after a long period of practice, I can get some experiences to share with some people here. 🙂
From my experience you are an asset to this forum! Thanks again! (if you are stupid what am I? 🙁 LOL)
Hi,
me again. I'm still wondering about this. Was the original transistors faulty? But if it is then why did it pass the diode test? Thanks
me again. I'm still wondering about this. Was the original transistors faulty? But if it is then why did it pass the diode test? Thanks
It is the temperature problem, small signal transistor working in high temperature for a long time, the transistor die became unstable(physical damage) and if the high temperature condition is continue the transistor will be failed one day.
So is the other model transistor actually better? I haven't done anything since we last spoke, I'm just planning it out in my head what I'm going to do.
You can said like that, but they are also suffering from high temperature.
For safe and balance between amps, better make same change to the other amp.
Sorry, I misunderstood your question in #91.
Yes, in the last changed to transistors ZTX653 and ZTX753, they are more suitable for working in higher current than the original transistors. Last time also reduced the running current for these two transistors, so that no need put heatsink.
You can keep using these new transistors ZTX653 and ZTX753 in your amp.
Best regards.
Last edited:
Just wanted to post my thanks for this particular thread. My XA50 pair went faulty years ago & got put in the attic. I wanted to get them back in use & this thread was extremely helpful. Both the schematic & the guidance on the current source transistors. Mine are now recapped (high spec in the feedback & input caps) and the circuit has been modified to reduce the current flow through the two transistors. That’s all it took to fix one but the other needed driver & output transistors after TR6 gave up the fight.
now running direct to a DAC pre & they sound surprisingly good.
now running direct to a DAC pre & they sound surprisingly good.
Hi, any more details? What resistors did you use? And what did you replace the transistors with? Thanks
Followed the suggestions earlier in the thread. Replaced R10 with 68ohm resistor instead of 47ohm, to reduce the current flow through TR6 and TR8. Those items were also replaced in both amps with a pair of ZTX653/753. The driver transistors are also ztx653/753 and the output transistor is a Musical Fidelity coded part but replaced with TIP35C based on internet info and that seems to work but i don’t think they are an exact match to the original parts.
I tried the 653/753 but I found they got too hot and the DC was rising. I actually didn't do much more to mine since it was fixed. Its very nice to hear others have fixed their amplifiers too!
They do run warm to the touch (in the heavy tube case) and always did. Perhaps a little more with the bias set to 4mv. I think it was originally set to 1 or 2mv but the scope signal looked better at 4mv.
what else did you replace on yours? Most of my caps “appeared” okay & measured okay on a DMM but I don’t have an ESR meter & had a set of fresh electrolytic caps anyway.
what else did you replace on yours? Most of my caps “appeared” okay & measured okay on a DMM but I don’t have an ESR meter & had a set of fresh electrolytic caps anyway.