Hello all! I have modded one of my tubeamps by removing a resistor and adding a 6AK5 gain stage and it sounds more beautiful than ever. 
Heres the schematic, i dident include the power supply as its still the same and can be seen in other schematics.
Heres the schematic, i dident include the power supply as its still the same and can be seen in other schematics.
An externally hosted image should be here but it was not working when we last tested it.
Hello! Good! It seems a good amp.
Is it an american amp? That's because of the 6l6 outputs...
How do these sound in hi-fi? I only know them in guitar amps...
And that input pentode stays quiet or it is microphonic like many small pentodes?
You also have some strange capacitors values (235uF? )...
What resistor have you changed?
Is it an american amp? That's because of the 6l6 outputs...
How do these sound in hi-fi? I only know them in guitar amps...
And that input pentode stays quiet or it is microphonic like many small pentodes?
You also have some strange capacitors values (235uF?
)... What resistor have you changed?
6L6GC is a very good tube in HIFI, actually it was designed for PA amps tho. The resistor i removed was between the 120µF and 100µF cap on the schem, why some of the cap values it odd is because its 470µF caps in series. I built this amp from scratch using chassis, OPT and PT from a old organ amplifier, the guys on geek.scorpiorising.ca helped me with the design of the amp. The input 6AK5 is microphonic, you hear *dinnnnggg* in the speaker if you tap it, you even hear some faint clicks with a echo effect when you turn B+ on from the cathode and grids when they heat up.
The input 6AK5 is microphonic, you hear *dinnnnggg* in the speaker if you tap it, you even hear some faint clicks with a echo effect when you turn B+ on from the cathode and grids when they heat up.
Oh yes, that resistor is just useless (if not bad) when there's already a choke to isolate the driver stage from the outputs. Good design!
I bet that every pentode you tried in the input stage was microphonic... I remember a design somewere that used a power pentode as an input, maybe a 6V6 or similar might work... they are less microphonic (but worse sounding)... just to try...
I didn't know that 6L6 were used in hi-fi (other than in american designs). I supposed that beam power tetrodes just don't cut it in high-fidelty outputs... What are their sonic characteristics against well known outputs (EL34, EL84, KT88, 6550...).
Edit: oh sorry actually some of the tubes I mentioned as regulars hi-fi are in fact beam pentodes...
I bet that every pentode you tried in the input stage was microphonic... I remember a design somewere that used a power pentode as an input, maybe a 6V6 or similar might work... they are less microphonic (but worse sounding)... just to try...
I didn't know that 6L6 were used in hi-fi (other than in american designs). I supposed that beam power tetrodes just don't cut it in high-fidelty outputs... What are their sonic characteristics against well known outputs (EL34, EL84, KT88, 6550...).
Edit: oh sorry actually some of the tubes I mentioned as regulars hi-fi are in fact beam pentodes...
Heres some pics of the thing:
Notice the cable to the metal screen on the 6AK5:
The amp from above:
Notice the cable to the metal screen on the 6AK5:
An externally hosted image should be here but it was not working when we last tested it.
The amp from above:
An externally hosted image should be here but it was not working when we last tested it.
Hi Giaime,
Many 7581A's over here are labled KT-66 also. On the same bottle. When I looked KT-66 up I see plate diss ratings of 25 and 30W depending on the source. The 6L6GC is indeed 30W as you stated, the 5881A is 25W. THe 6550A and KT-88 I see rated at 42W diss.
So there is some confusion on the KT-66 rating (I've always assumed it was 35W due to the dual branding on the 7581A).
So aside from that, do you see any other errors?
-Chris
Many 7581A's over here are labled KT-66 also. On the same bottle. When I looked KT-66 up I see plate diss ratings of 25 and 30W depending on the source. The 6L6GC is indeed 30W as you stated, the 5881A is 25W. THe 6550A and KT-88 I see rated at 42W diss.
So there is some confusion on the KT-66 rating (I've always assumed it was 35W due to the dual branding on the 7581A).
So aside from that, do you see any other errors?
-Chris
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