I don't know what happened but I powered the other channel and all OK.
So I swapped out the tfos and now, both channels bias up perfectly to about 1.25 V
dc offset on outputs are about 3 mv.
sinks are warming up nicely but take about 10 minutes to get to hottest point.
The only issue now is the offset. turning the offset pot has no effect on dc output. Unless I misunderstood something about the offset pot???
tweaking the harmonics pots is next...
So I swapped out the tfos and now, both channels bias up perfectly to about 1.25 V
dc offset on outputs are about 3 mv.
sinks are warming up nicely but take about 10 minutes to get to hottest point.
The only issue now is the offset. turning the offset pot has no effect on dc output. Unless I misunderstood something about the offset pot???
tweaking the harmonics pots is next...
I'am currently at the same spot you are (thanks Buzz) finally got bias to 1.5A and now trying to learn best way to adjust harmonics
I need help with a new problem, one side is oscillating (I think) off set is jumping all over the place from 0 to 18v rapidly + side led is blinking slowly and R13 gets too hot very fast!
bias moves around but not near as much as offset. I have checked everything closely and can't see anything wrong. Swapped transformers and problem stopped but came back, other side remains rock steady with ether transformer Stumped
bias moves around but not near as much as offset. I have checked everything closely and can't see anything wrong. Swapped transformers and problem stopped but came back, other side remains rock steady with ether transformer Stumped
Try larger gate resistor. Make double sure that the transformers are oriented correctly and that all pins are well soldered. Check continuity of the transformer connections on board with power turned off. I had this trouble once and it amounted to a pin not being soldered in on the pcb.
I suspect "motorboating". The F6 has poor phase margin at very low frequencies (< 1Hz) that I reported very early in this thread http://www.diyaudio.com/forums/pass-labs/216616-f6-amplifier-102.html#post3136046. Try decreasing the values of C1 and C2 from 1000uF to 470uF. That helped for me.
Try larger gate resistor. Make double sure that the transformers are oriented correctly and that all pins are well soldered. Check continuity of the transformer connections on board with power turned off. I had this trouble once and it amounted to a pin not being soldered in on the pcb.
I had a similar problem and it was a colder solder joint - actually I forgot to solder a transformer lug.
generg - did you also have something similar?
Best
Bob
I resoldered all the trans points on the board no need to do sister board as the trans works fine on the other side. Problem is better but offset still unstable, but down in mv range now, While increasing bias and after 1.2a problems gets worse. after getting bias stable and offset down(still jumping around some) I hooked up speaker and it has a very audible hum other channel is dead quiet. If boards are built identical why is one side so cantankerous?? or why the need to try different component values? Just asking
I favor this motorboating diagnosis too; to also suspect a bad/leaky electrolytic cap.I suspect "motorboating". The F6 has poor phase margin at very low frequencies (< 1Hz) that I reported very early in this thread http://www.diyaudio.com/forums/pass-labs/216616-f6-amplifier-102.html#post3136046. Try decreasing the values of C1 and C2 from 1000uF to 470uF. That helped for me.
Would anyone have any 2SJ74 BL to sell?
Been searching ebay too... Not sure how to recognize originals from copies... Does TOS in front of the item mean Toshiba? The Chinies not originals? 😕
Been searching ebay too... Not sure how to recognize originals from copies... Does TOS in front of the item mean Toshiba? The Chinies not originals? 😕
It is easiest to assume all Ebay J74/K170 are fake.
Spencer has real ones - FET Audio | Hi-End Audio ProjectsStore | FET Audio
Spencer has real ones - FET Audio | Hi-End Audio ProjectsStore | FET Audio
Thanks guys!
I think I'll lean towards Linear Systems - it's not cheap though... but they are available.
Any idea why the C grade is cheaper than the B grade? Which one would be best for FirstWatt applications?
Also... It seems I can get 2SK170 10mA from local store, but would it be less wise to mix 2SK170 and LSJ74?
I think I'll lean towards Linear Systems - it's not cheap though... but they are available.
Any idea why the C grade is cheaper than the B grade? Which one would be best for FirstWatt applications?
Also... It seems I can get 2SK170 10mA from local store, but would it be less wise to mix 2SK170 and LSJ74?
buy them if they're originals
no harm in mixing these two
A, B , C means GR , BL , V
best to look for BL for Papa's gizmos
no harm in mixing these two
A, B , C means GR , BL , V
best to look for BL for Papa's gizmos
I resoldered all the trans points on the board no need to do sister board as the trans works fine on the other side. Problem is better but offset still unstable, but down in mv range now, While increasing bias and after 1.2a problems gets worse. after getting bias stable and offset down(still jumping around some) I hooked up speaker and it has a very audible hum other channel is dead quiet. If boards are built identical why is one side so cantankerous?? or why the need to try different component values? Just asking
Double check PSU wires as well as input and output ground connections. If that doesn't fix it, then try switching caps to lower value. Perhaps it is motor boating on you. Doesn't sound like it from my experience, but been wrong too many times before.
Checked all connections on psu ( I'am using my F5 ps that was working fine) changed caps to a lower value....no change. + side led is blinking and offset jumps around. things change a little when I hook up a speaker led stops blinking but speaker hums pretty badly. I don't remember the exact amount but there is both ac and dc present at the speaker post ?? dc is in mv maybe 30-50 but wants to stay on the - side, I can get it to + by lowering the bias to about 1.0a LOST 🙁
The effect you mentioned happened to me only when I had changed in my point to point F6 by accident the polarity of the windings.
For sure you have a heavy oscillation. When you use tea-bags wonderfull pcb and you have this effect.....
I would guess.....
One xformer is damaged and one or more windings are gone
A soldering in the adapter board or in the motherboard is not working.
Hope it is one of these things.....
For sure you have a heavy oscillation. When you use tea-bags wonderfull pcb and you have this effect.....
I would guess.....
One xformer is damaged and one or more windings are gone
A soldering in the adapter board or in the motherboard is not working.
Hope it is one of these things.....
Both transformers work fine in the other side so the problem has to be on the mother board
I have re soldered the tm connections but I guess i'll go over them again tonight.
I have re soldered the tm connections but I guess i'll go over them again tonight.
The 2SK170 at the local store were Toshiba ...but not BL, only low GR grade.
And the DiyAudio store is out of B grade LSK170. Bummer. 🙁
And the DiyAudio store is out of B grade LSK170. Bummer. 🙁
Are there any grades with the IRFP parts (like with the jfets K170 and j74)? They do seem to have different markings on them. This what we have at the local store.
https://www.facebook.com/photo.php?...29169456.10665.100001684484838&type=3&theater
Sorry for all these simple questions, but when you don't you don't know...
https://www.facebook.com/photo.php?...29169456.10665.100001684484838&type=3&theater
Sorry for all these simple questions, but when you don't you don't know...
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