Fully agree. I also suspect something happened at the gate connection. Maybe suddenly the gate had no longer a connection to ground and the amps started going high?
Auto bias is the safest principle with the minimum parts (At the expense of about 20 watts in the present case...) and i would not question it.
I would really love to keep this amp. I put quite some effort into it.
I think I have a set of these I never have put to use...
Hello Skorpio
Thats good news. KD33 types are probably the only ones that we can reasonably use with auto bias. The other types require higher bias voltages and this will result in too much heat dissipation at the source resistors. Or am i wrong?
I shall send you a private mail.
Many thanks
More good news! Skorpio did not reply yet to my mail. If by Monday nobody comes forward i shall go for the p_channel option. (And keep in mind Murphie's law: " the fewer the parts, the bigger the chance for a wrong connection)
Jost
thanks alot for the info.!.!
(so..if i want air-core chokes for my L'Amp i have to wind them myself)
I have a single piece of 2SK82 KT-33 that I'm willing to offload, as it's pinch off voltage is rather lower than my stock of KD/E/F-33s.
KT-33 is not very common so you may doubt it's authenticity, but as far as I can tell and measure, it's a real Sony 2SK82 with same trans-conductance as the KD/E/F-33s.
PM me if interested.
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thanks alot for the info.!.!
(so..if i want air-core chokes for my L'Amp i have to wind them myself)
The Multilayer Air Core calculator from Pronine is more convenient, but the results are the same..
You are right. But in this case it would only affect the frequencies below appr. 100Hz wouldn't it?
I did the required changes and while doing that, i discovered a bad solder point that eventually had resulted in cutting the connection from gate via the 47k to ground.
This is what i know and what i am absolutely sure about.
When testing both SITs with the Ohm meter, to my surprise both measured the same.
Followed start up and everything was normal again. Rock solid values during 4 hours and music just fine.
These SITs are solid, almost as triodes
Many thanks again to you and propotki for your hints and advice
Interesting. Had a closer look at the link (by the way i like a lot his work regarding high efficiency speakers)
The placement of the coils in my amp is less than optimal. But at least they are far away from aluminum housing. I almost exlusively use wood.
Now to increase inductance it would be nice to place them side by side, like too wheels. A friend of mine suggested exactly that for aesthetic reasons. But then i had made the box already and there was not enough space on that box and not enough will to make another, bigger one.
These coils are somewhat monuments of the 19th century Frankenstein and as lying rolls they shine even more.
They are peers of the engines in the picture below.
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hmm, yeah, i checked that. and the difference is quite substantial
i wonder why is that so...
... and i´m glad to hear your amp playing music again !!
I did the required changes and while doing that, i discovered a bad solder point that eventually had resulted in cutting the connection from gate via the 47k to ground.
This is what i know and what i am absolutely sure about.
When testing both SITs with the Ohm meter, to my surprise both measured the same.
Followed start up and everything was normal again. Rock solid values during 4 hours and music just fine.
These SITs are solid, almost as triodes
Many thanks again to you and propotki for your hints and advice
It's great to hear it gets up running again.
Can you tell the different with adjustable bias and auto bias. I mean which one you like the most.
did you find any strange sound before? great news SIT survived. once i set Vbias in opposite way, so it was biased with +4VI did the required changes and while doing that, i discovered a bad solder point that eventually had resulted in cutting the connection from gate via the 47k to ground.
This is what i know and what i am absolutely sure about.
When testing both SITs with the Ohm meter, to my surprise both measured the same.
Followed start up and everything was normal again. Rock solid values during 4 hours and music just fine.
These SITs are solid, almost as triodes
Many thanks again to you and propotki for your hints and advice
i heard distorted music but i needed about 10sec to realize something was wrong on the circuit, but got no any smokeit seems that SIT can absord human error, to give more courage on experiment.
With regard to music i could not tell. Both sound good.
I have no direct comparison or i would have to make it by doing one channel self bias the other fixed.
There are advantages, disadvantages and constraints for both...
Self bias:
Safest mode for SIT
20 watt higher power consumption (@ 1.63 amps/channel)
Requires extra heatsink for source resistors
Requires higher B+
Tuning to find optimum operation point for low distortion requires either change of B+ or source resistor value
(i use a quasi choke input power supply where i can tune the voltage through C1 c.f picture)
Fixed bias:
Not intrinsically safe mode for SIT
Requires additional power supply
Lowest power consumption
Lower B+ (The "standard" 24V supply will do)
Easy to tune for low distortion
Jost
