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Sony 2SD45 replacement transistor for TA-1120A?

fandersen

fandersen

Active Member
I have a Sony TA-1120A that needs at least one 2SD45 power transistor and I am having difficulties finding a recommended replacement. I don't have a lot of experience finding suitable replacements for transistors but the MJ15015 or MJ15022 look like possible candidates. Can anybody confirm these would be suitable replacements or recommend a better alternative?

Thanks
 
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I also have this amplifier. What I would do is finding a vintage but good 2N3055, as it would have a comparable bandwidth as the Sony original. The types you suggest have higher bandwidth and could bring oscillation problems.
After your fix, I would like to know if you also experience the typical behaviour of this Sony: volume control over 12 o'clock for decent volume level.
 
How do you determine the bandwidth of a transistor from the specifications? Is it the Ft? From what I could determine the 2SD45 has a Ft of 10MHz. From the onsemi specifications the 2N3055 has a Ft of 2.5. The 2N3055A and MJ15015 have Ft of 0.8-6.0. Just trying to understand this a little better.

While diagnosing this problem I did notice that the preamp doesn’t produce any significant volume until after 12 o’clock as you indicated. So once fixed I would expect this unit to be the same. My testing was through the AUX input which has a level adjustment.
 
I'm trying to understand transistor selections a little better. In the attached image would I be correct in saying that minimum value for Vceo is 50.7V and minimum value for Vcbo is 49.8V?

voltage.png
 
The reference (zero) is the ground line.

The DC output voltage (NO signal present) is the 42.3 target value in the middle. Be aware: the output can swing up to almost positive and negative "rail voltage", practically this means you will need to have transistors capable of widthstanding 90 Volts collector to base and collector to emitter.
FT figure itself is not that important but it gives some indication, what is important you still want some amplification at higher currents and those MJ will do fine although FT is lower than the original.
2N3055 officially is 60 Volts only so using them would be risky. Myself I would choose MJ15022 over MJ15015 because of better ruggedness and somewhat better amplification at higher currents.
 
I installed 8 new MJ15022 tonight, set the bias and DC offset. I need to do a little more listening but initial impressions are very good. :thumbsup:
 
GrundigXpert said:
After your fix, I would like to know if you also experience the typical behaviour of this Sony: volume control over 12 o'clock for decent volume level.
Click to expand...

I get no volume until the 9 o'clock position on the volume control, then a gradual increase in volume until the 12 o'clock position where the volume significantly increases. I guess it's just the curve of the volume control.
 
Nice work on getting her up and running :thumbsup:.

I have also experienced some of the early Sony's having a different volume control curve to other units.
 
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