I gave him a twin brother 
Now I must give them an House $$$$$ €€€€€
And now, They are playing in stereo
I have only one word to define the sound. Natural.
I have made some new measures.
The clipping, without load is simmetrical at +22.45 -22.75.
Under 8 hom load it is not +18.72 -21.2
The voltage drop at +/- 1.25V is 63mV so OI is 0.42 and DF is 18.8.
At +/-3.45V is 310 mV so OI is 0.8 and DF is 10
At clipping on the minus VD is 1.57 on the + is 3.74 and I don't know which one to use.
Offset rises as the volume goes up, reaching about 800 mV just before clipping. I don't know if this is normal or not.
Maybe swapping the 140N with a 240 could improve the performance. I have read somewhere that this pair is well matched. Have you any advice on this question?
Now I must give them an House $$$$$ €€€€€
An externally hosted image should be here but it was not working when we last tested it.
And now, They are playing in stereo
An externally hosted image should be here but it was not working when we last tested it.
I have only one word to define the sound. Natural.
I have made some new measures.
The clipping, without load is simmetrical at +22.45 -22.75.
Under 8 hom load it is not +18.72 -21.2
The voltage drop at +/- 1.25V is 63mV so OI is 0.42 and DF is 18.8.
At +/-3.45V is 310 mV so OI is 0.8 and DF is 10
At clipping on the minus VD is 1.57 on the + is 3.74 and I don't know which one to use.
Offset rises as the volume goes up, reaching about 800 mV just before clipping. I don't know if this is normal or not.
Maybe swapping the 140N with a 240 could improve the performance. I have read somewhere that this pair is well matched. Have you any advice on this question?
Bobo, I don't know how distorsions rises lowering the bias, but for shure, just listening, these distorsions don't seem to annoy the ear. The ampli has an his imprint, and I don't think it will change so much increasing the bias. At most it can increase the depth of the soundstage a little.
At the measures, probably the thing will be different.
Andrew, I know perfectly that heatsink is not enough for one channel, but at least I am listening at a F5 having spent 45€ for the PS, and having everything else on the shelf, so now I can decide if to spend other money for box and heatsink, or not, and since it seems that it is worthwhile, I am going to order this onee for 185€ out of the door.
Do you think i'ts enough?
At the measures, probably the thing will be different.
Andrew, I know perfectly that heatsink is not enough for one channel, but at least I am listening at a F5 having spent 45€ for the PS, and having everything else on the shelf, so now I can decide if to spend other money for box and heatsink, or not, and since it seems that it is worthwhile, I am going to order this onee for 185€ out of the door.
Do you think i'ts enough?
An externally hosted image should be here but it was not working when we last tested it.
4U may work, depending on air temperature
Heat sink is 300x165x40
My guess is that its Fischer heatsink
Sk501 sem to fit the specced size used in modushop box
Increasing from 150mm to 200mm height doesnt seem to make significant improvement
Its about 0.3K/W in both sizes
Curve is almost horisontal at 150mm height, so no further improvement with increased size, it seems
But 40mm fins is on the small side and not the most effective
SK157 from Fischer has 83mm fins, that seem to be very effective
Its close to 0.2K/W at 200mm, and still more to gain, it seems
Heat sink is 300x165x40
My guess is that its Fischer heatsink
Sk501 sem to fit the specced size used in modushop box
Increasing from 150mm to 200mm height doesnt seem to make significant improvement
Its about 0.3K/W in both sizes
Curve is almost horisontal at 150mm height, so no further improvement with increased size, it seems
But 40mm fins is on the small side and not the most effective
SK157 from Fischer has 83mm fins, that seem to be very effective
Its close to 0.2K/W at 200mm, and still more to gain, it seems
good post 
> while the J74 varies between -500 and -1500 mV?
Did you mean between -500 and -1500 mV or between 50 and 150 mV ?
If you meant -500 and -1500, then it is not normal. Firstly I expect your Idss to be larger than 6mA, in which case Vgs should be POSITIVE and not negative for 2SJ74, and vice versa for 2SK170.
But suppose that Vgs is positive, and even with the V-grade at 16mA Idss, the Vgs should not be more than +400mV at 6mA bias. Please refer to Page 2 of datasheet.
If you indeed measured -1500mV (i.e. the gate voltage is lower than source), you are for certain forward biasing the JFET, and I would have expected a much larger current than 6mA.
Or I misunderstood you completely.
Patrick
Did you mean between -500 and -1500 mV or between 50 and 150 mV ?
If you meant -500 and -1500, then it is not normal. Firstly I expect your Idss to be larger than 6mA, in which case Vgs should be POSITIVE and not negative for 2SJ74, and vice versa for 2SK170.
But suppose that Vgs is positive, and even with the V-grade at 16mA Idss, the Vgs should not be more than +400mV at 6mA bias. Please refer to Page 2 of datasheet.
If you indeed measured -1500mV (i.e. the gate voltage is lower than source), you are for certain forward biasing the JFET, and I would have expected a much larger current than 6mA.
Or I misunderstood you completely.
Patrick
Hi Patrick. Thank you for the answer.
I arranged this small schematic, and the values I have read between ground and source are from -500 to -1500 with the most, on 30 units, between -800 and -1300 mV. Only one is -60 mV.
I arranged this small schematic, and the values I have read between ground and source are from -500 to -1500 with the most, on 30 units, between -800 and -1300 mV. Only one is -60 mV.
An externally hosted image should be here but it was not working when we last tested it.
