6V6 line preamp

[Salas]

Save your money. ;-)

If the filament supply has 1.2A per tube capability there is opportunity to drop in test the lower voltage higher Gm spec 6W6GT.
Its a dirt cheap NOS variety because not in demand due to weak voltage spec for the average guitar amp's plate and screen rails.
But the G3X pre doesn't use it like that. No problemo. It will probably give same THD figures but with halved output impedance.
Has much stronger heater to support its wide cathode. Originally used in TV sets to produce more current at lower rail voltages.
Expect 25-45V lower plate voltage and 5-10mA higher bias current when dropped in any existing Salas 6V6 preamp schematic.

 

[grovergardner]

Happened the same with expensive Melz 6N8S 1578 metal base hole round plate....

Interesting!

 

[merlin el mago]

I'm using 7N7 at Valve Itch but still not satisfied with the sound, before used the standard 6H8C as Salas used & tried also the 1587 but both not my cup of tea, I'm looking for a sound with more mids & bass.

 

[grovergardner]

FWIW, GE 6SN7GTA or GTB always my go-to tube. Full sound, nothing pushed out or recessed. Cheaper than new stock!

 

[Salas]

Valve Itch phono can also accept the noval base 6DJ8/ECC88 in its output stage. Drop in same circuit values just gives bit stronger gain. There are several classic makes including Amperex Bugle Boy still circulating out there.

 

[merlin el mago]

Really don't need more gain because 1587 have more gain, what I'm looking for is other kind of sound more robust, with more mids & bass.

 

[Salas]

You are after classic British sound. Its a pity Mullard ECC32 etc. cost a fortune these days.

 

[merlin el mago]

There is nothing more cheap Salas?

 

[Salas]

The grovergardner recommended GE is safe and economic to taste. You could also doctor the RIAA curve to bassier with more pF on C3. But this is a detail for the phono thread.

 

[merlin el mago]

Yes you are right Salas better at the Valve Itch phono thread.

 

[merlin el mago]

FWIW, GE 6SN7GTA or GTB always my go-to tube. Full sound, nothing pushed out or recessed. Cheaper than new stock!

Thank you.

 

[merlin el mago]

Just arrived the Vishay Dale CMF55 & the Ohmite Audio Gold 10W (Salas I know isn't necessary the high power wattage, but it's to compare vs the Mills MRA-12W for cathode.

 

[merlin el mago]

Salas I guess for NFB version without volume pot have I to not use 1K grid stopper resistor nor 1Meg leak resistor right? Of course have I to add the NFB, I ask because at the moment I will use for noDac line level amplification not line level preamp?

 

[Salas]

The Ri plays the grid stopper's role too. The RLo 470k output to ground resistor gives reference to the feedback path but better put another 470k where there would be an input volume pot. For ground reference double safety.

 

[merlin el mago]

Could I left the 1Meg as volume pot? If not no problem I look for others 470K or parallel two 1Meg, of course before Ri in place of volume pot.

 

[Salas]

Datasheet has max 2.2 Meg grid 1 resistor in triode mode cathode bias operation. So 1 Meg you can.

 

[merlin el mago]

Only to be sure attached schematic, TIA Salas to check it.

 

[merlin el mago]

Work in progress

 

[merlin el mago]

Only to be sure attached schematic, TIA Salas to check it.

It's OK the attached schematic Salas?

 

[Salas]

OK