It was emitter voltage that I measured but inadvertantly, I typed base.
The post was edited.
Actually your post was not edited.
Anyhow, the voltages you write are not big enough so you need to adjust the resistors as @Mooly suggests
I see that. I revised the word and saved the change within the 1 hour window.
I should be able to do that on Tuesday, when the resistors arrive.
@Mooly
@madis64
@poundy
The latest batch of resistors arrived today. I first replaced the somewhat newly installed 820 ohm 1/2 watt resistors with 1 watt. Then manipulated the amplifier's face so as to access the controls and played a CD via a Discman. Speakers were a pair of Realistic Minumus 7. DBT did not brighten one bit and the music sounded good. Or as good as Minumus 7's can sound. I switched to headphones and they sounded better.
I next paralleled the 2.2K ohm resistor at R308 with a first suggested 4.7K ohm resistor and that was spot on. Bias is now adjustible from 0.0mV to well past 100mV causing the DBT to start glowing. I then did likewise with R408 and the result was identical.
After 220 posts, it looks like this amplifer is completely functional. I hope that claim does not invite disaster. I still need to make a final bias adjustment and re-assemble it.
Regarding that final bias adjustment, is the factory specified 25mV the optimum setting with all the new transistors?
I truly wish to thank all of you for the patient hand holding that guided me to what seems to be a happy ending, The willingness with which you share your considerable knowledge and expertise is is astounding and very much appreciated. I owe a debt I cannot repay.
Unless it's with a killer recipie for dog buscuits.
@madis64
@poundy
The latest batch of resistors arrived today. I first replaced the somewhat newly installed 820 ohm 1/2 watt resistors with 1 watt. Then manipulated the amplifier's face so as to access the controls and played a CD via a Discman. Speakers were a pair of Realistic Minumus 7. DBT did not brighten one bit and the music sounded good. Or as good as Minumus 7's can sound. I switched to headphones and they sounded better.
I next paralleled the 2.2K ohm resistor at R308 with a first suggested 4.7K ohm resistor and that was spot on. Bias is now adjustible from 0.0mV to well past 100mV causing the DBT to start glowing. I then did likewise with R408 and the result was identical.
After 220 posts, it looks like this amplifer is completely functional. I hope that claim does not invite disaster. I still need to make a final bias adjustment and re-assemble it.
Regarding that final bias adjustment, is the factory specified 25mV the optimum setting with all the new transistors?
I truly wish to thank all of you for the patient hand holding that guided me to what seems to be a happy ending, The willingness with which you share your considerable knowledge and expertise is is astounding and very much appreciated. I owe a debt I cannot repay.
Unless it's with a killer recipie for dog buscuits.
Surprisingly perhaps but yes it does appear to be the optimum theoretical value. What you will find in practice is that even a very tiny bias current removes any audible distortion and what I would say is don't be tempted to go higher. You won't gain anything and it only generates more heat.
Make sure the final setting is with the amp fully warmed up and running on full mains (no bulb)
And of course 🙂 thanks for the kind words and I think we are all pleased it is working 👍. It has been quite a journey.
I have to add a follow up.
I've been listening to this Sony amp for several days now. I did have it working prior to the mishap that started this thread and I thought that it sounded OK during that time.
I may have disclosed early on that I bought a brand new Sony TA-1150 in 1973 to go along with a pair of Large Advent loudspeakers. It was the salesperson's recommendation. While I cannot remember in exquisite detail what that combo sounded like, I do remember being enormously happy with the bass response.
While this amp was laid up for the months that this thread progressed, I was using a compltely recapped, MOSFET equipped Sanyo Plus P55 power amp and an extensively rebuilt Hafler DH-101 pre-amp. My current speakers are Polk Monitor 5B with the upgraded "new" tweeter. That setup was OK but did not thrill me to pieces.
Sound quality was better I thought when playing tape recordings than it was with with vinyl or CD.
So now, with this resuscitated Sony, I seem to be blessed with a more enjoyable sound than what was provided by the power/pre pair. The Sony certainly sounds better than it once did not all that long ago, and makes me think that maybe it is as good as it ever was when brand new. I am surprised / impressed at the bass output of these Polk speakers. I was expecting them to be decent in that regard but with this Sony amp, they surpass my expectation.
FWIW, when I bought the Advent speakers and Sony amp in 1973, I remember being shown a bulletin from the Advent Corporation. It was basically a list of a few amplifiers recommended as being a good match for their speakers. A Sony TA-1150 was one of them.
EDIT: A small turn off thump had been present but that is gone now.
I've been listening to this Sony amp for several days now. I did have it working prior to the mishap that started this thread and I thought that it sounded OK during that time.
I may have disclosed early on that I bought a brand new Sony TA-1150 in 1973 to go along with a pair of Large Advent loudspeakers. It was the salesperson's recommendation. While I cannot remember in exquisite detail what that combo sounded like, I do remember being enormously happy with the bass response.
While this amp was laid up for the months that this thread progressed, I was using a compltely recapped, MOSFET equipped Sanyo Plus P55 power amp and an extensively rebuilt Hafler DH-101 pre-amp. My current speakers are Polk Monitor 5B with the upgraded "new" tweeter. That setup was OK but did not thrill me to pieces.
Sound quality was better I thought when playing tape recordings than it was with with vinyl or CD.
So now, with this resuscitated Sony, I seem to be blessed with a more enjoyable sound than what was provided by the power/pre pair. The Sony certainly sounds better than it once did not all that long ago, and makes me think that maybe it is as good as it ever was when brand new. I am surprised / impressed at the bass output of these Polk speakers. I was expecting them to be decent in that regard but with this Sony amp, they surpass my expectation.
FWIW, when I bought the Advent speakers and Sony amp in 1973, I remember being shown a bulletin from the Advent Corporation. It was basically a list of a few amplifiers recommended as being a good match for their speakers. A Sony TA-1150 was one of them.
EDIT: A small turn off thump had been present but that is gone now.
I'm pleased to hear your enjoying the repaired amp and there is no reason it shouldn't be any different sound wise than when it was new. A lot of older gear does sound really good 🙂