6V6 Pentode PP

Hi!

Im gonna make some drastical and hopefully last changes to my preamp.
Im gonna build another psu and change 6sn7 output tubes for 6V6 in Pentode connection.
Attached is part of the circuit , not showing the first tube and global feedback etc.
Since i havnt worked with pentodes before i wonder if this setup is acceptable.
Im mostly worried about the shared CCS on the cathodes and if anything can go wrong with the screens which will have separate regulated voltage.
the voltages and bias is a little bit of guess work with the help of average plate transfer curves and loadlines from plots with higher screen voltage and higher plate current.

Why isnt the 6SN7 adequate ? hows is the phase invertion arranged ?

5v333 said:

Hi!

Im gonna make some drastical and hopefully last changes to my preamp.
Im gonna build another psu and change 6sn7 output tubes for 6V6 in Pentode connection.

Click to expand...

6V6 in a preamp? You could drive a speaker...

[/quote] Im mostly worried about the shared CCS on the cathodes and if anything can go wrong with the screens which will have separate regulated voltage. [/quote] I would recommend screen resistors.

Tubetec said:

Why isnt the 6SN7 adequate ? hows is the phase invertion arranged ?

Click to expand...

The OT is a 9:1 (half sec is used for feedback). The somewhat high ratio steals some voltage headroom.
with a good bias point, both input and output  headroom was somewhat comprimised. this was something i was more or less ok with.
then i discovered that the last fundamental problem is the LF bandwidth of the OT and needed much more loading to have a low enough f3.
Abbey had warned me about this some time ago but i made my best trying to ignore it, hoping that everthing  would work out soundwise.
the 6sn7 is quite good around 15k load(for one plate), i was aiming for 30k for good linearity and maintaining enough gain.
hower with a load of 7500 or lower, thd and gain just collapses.


theres an input phase splitting transformer earlier on.

abbey road d enfer said:

6V6 in a preamp? You could drive a speaker...

Im mostly worried about the shared CCS on the cathodes and if anything can go wrong with the screens which will have separate regulated voltage.  I would recommend screen resistors.

Click to expand...

yes it can drive speakers
a good thing i guess haha!
After going through a couple of alternatives and their curves i got a very good feeling about the 6v6. also it was used by RCA in the BA6A Limiter.

would the screen resistors keep the current regulated (and therefor not messing with the total current bias ) or would it limit massive current draw when grid approaches 0V?

5v333 said:

it was used by RCA in the BA6A Limiter.

Click to expand...

There's a gfood reason for that; they have to drive the side-chain detectorthat has an impedance of about 10k. that would suck the juice out of a low-level tube.

would the screen resistors keep the current regulated (and therefor not messing with the total current bias ) or would it limit massive current draw when grid approaches 0V?

Click to expand...

Screen resistors are usually low value (about 1k) so there's no significant loss of regulation, and yes they're here for protection.

I forgot about the sidechain...

Thanks for the info about the screen resistor!