6V6 line preamp

[Salas]

@kodabmx
Well, when your Cinput serves a special function its justified.

 

[Salas]

By the way someone asked me what is the music in the short video clip I posted in #4,166.
Its Dexter Gordon's hard bop style Jazz album One Flight Up. Grado Master3Low, UFSP ph.

 

[merlin el mago]

Salas unfortunately don't have on hand the voltage divider resistors values at the input, could I use others values? For example 100K for Ri & 1Meg for Rf?

 

[Salas]

Yes for now, but also get the ones I advised to replace. Because 100k Ri limits bandwidth more. The tube and socket have capacitance and the gain gives Miller, so an RC filter is formed. Ri + Rf solder them meeting directly on the socket's grid pin to avoid using wires giving extra capacitance.

 

[merlin el mago]

I could do 100R & 1K? 6k2 & 56k?

 

[Salas]

No, too small for input impedance and heavy load down because this is shunt NFB (Rf is essentially in parallel to Ra and Ri is essentially input impedance + little more from NFB)

 

[merlin el mago]

I have 82K also or 55K for Ri?

 

[merlin el mago]

NoDac output impedance is 50R

 

[Salas]

Not too far from 100k is 82k and will lose some gain. Live for now with right gain 100k/1Meg and 50kHz bandwidth. Later you buy good quality 63k/560k to replace for more bandwidth. Or even better two 120k in parallel for Ri for more precision. NoDac Zo maybe low but Ra is 7.5K and needs >>>Rf. Also Cout sees Rf as the impedance to drive.

 

[merlin el mago]

OK I will try with 100K/1Meg, thanks Salas.

How many mA draws each 6V6 to set the SSHV2 CCS?

If I like it with resistor loaded could I try with CCS or Gyrator?

Each heater draws 450mA?

 

[Salas]

Now you say you also found 55k in your parts bin. That can be combined with 1Meg//1Meg i.e. 500k Rf but you need four pieces.

 

[Salas]

No CCs anode load no gyrator. About 40mA is two channels draw. 20mA each.

 

[merlin el mago]

Now you say you also found 55k in your parts bin. That can be combined with 1Meg//1Meg i.e. 500k Rf but you need four pieces.

Fortunately I have four pcs. 1Meg. & four pcs. 110K to make 55K

 

[merlin el mago]

No CCs anode load no gyrator. About 40mA is two channels draw. 20mA each.

Do you want to say that resistor load is the best?

 

[merlin el mago]

Each heater draws 450mA?

 

[Salas]

Resistor load works with this NFB plan. If you change load to active, terra incognita. Yes each 6V6 wants 0.45A heater current.

 

[merlin el mago]

Thanks, attached files work in progress

 

[merlin el mago]

Resistor load works with this NFB plan. If you change load to active, terra incognita. Yes each 6V6 wants 0.45A heater current.

Let's see if one BiB can do it for both tubes.....

 

[Salas]

One L-Adapter is good too. Makes easy work of two heaters.
Brown resistor // green is 470Ω // 2k2 for 387Ω i.e. 390Ω Rk?
Those 470μF 63V Silmic II measure very good on the LCR by the way. I used them in my mod too.

 

[Lingwendil]

Thanks, attached files work in progress

Good work so far, my favorite construction style, just difficult to repair later.