larger tail resistor mistake?

[stevesamps]

I have built a cathode bias 6l6 amp with lowish plate voltages
the phase inverter is very similar to the 18W or vox like
with a 47k tail, this was actually a mistake but I like the amp
sounds I am getting,
what gives?

[Enzo]

What gives? You like the sound of your amp. You discovered that the part values are not set in stone and are not super critical. Enjoy. Feel free to experiment with other component values.

[Arthur B.]

I have built a cathode bias 6l6 amp with lowish plate voltages
the phase inverter is very similar to the 18W or vox like
with a 47k tail, this was actually a mistake but I like the amp
sounds I am getting,
what gives?

What do you like about the sound? A larger tail resistor would give better balance, but decreases the headroom.

[stevesamps]

I thought so I had at one time tweaked this value down
to about 20k , perhaps I like the sound of the PI clipping?
But headroom is a popular topic with guitarists.. for some reason

IS there any difference with this power amp being cathode bias?
regarding the headroom and tail ..?

[Bruce / Mission Amps]

What do you like about the sound? A larger tail resistor would give better balance, but decreases the headroom.


At around 36K to 56K I have not found that the larger tail resistor decreases headroom and it seems that if there is anywhere near normal preamp signals prior to the LTP phase inverter, adn it is operating at soldi B+ levels (not something silly like 150vdc) I hear a larger resistor resulting in slightly better head room.

Anyone else agree or disagree?

[Merlinb]

I think we're mixing up "headroom" with "output signal swing".
A larger tail resistor will drop more voltage, leaving less across the valve and therefore reducing the maximum output signal swing.
The headroom at the input to the PI is exactly the same as ever, depending on how you bias and what valve you use. Typically it will be between 0 and 8V p-p for an ECC83.

[Arthur B.]

I think we're mixing up "headroom" with "output signal swing".
A larger tail resistor will drop more voltage, leaving less across the valve and therefore reducing the maximum output signal swing.
The headroom at the input to the PI is exactly the same as ever, depending on how you bias and what valve you use. Typically it will be between 0 and 8V p-p for an ECC83.

No, I didn't confuse anything. I agree with you.

[stevesamps]

I tried an experimnent with this amp not very technical
just played through the amp and I had a switch that I was going to
use for a bright switch, I switched in an additional 47k across the
one in the amp and played a bit and listened, ..not much change
in tone a little tiny hair of a distortion difference but I settled
with the switch in, because it seemed to drive the 6l6's better
it had more girth and bottom end seemed like a tad more power..
very subtle though.. anyway I put a permanent 22k in there now
which what do you know is pretty standard..;)