F6 Amplifier

Jump to Latest
N

necplusultra

Member
Joined 2011
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...
 
M

mk57

Member
Joined 2011
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
 
buzzforb

buzzforb

Member
Joined 2010
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.
 
F

flocchini

Member
Joined 2004
buzzforb said:
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.
Click to expand...

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
 
M

mk57

Member
Joined 2011
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
 
A

Antoinel

Member
Joined 2011
jugi63

jugi63

Member
Joined 2004
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?
 
buzzforb

buzzforb

Member
Joined 2010
mk57 said:
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
Click to expand...

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.
 
M

mk57

Member
Joined 2011
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 :(
 
generg

generg

Member
Joined 2009
Paid Member
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.....
 
You must log in or register to reply here.
Top Bottom