Valve Itch phono

[Salas]

It shows more ground lines for not mixing return currents from different loops.

 

[RevoliAgain]

Thanks Salas. So no short cuts, do the job properly. My bread board build sounds great now so don't want to wreck it through careless build now. Anyone found good cable/cable shield available in uk? I would prefer nice metal shielding. Seems to only be sold by the reel.

 

[merlin el mago]

Finally arrived the Belton sockets (attached pic), I have several questions before starting the Salas Valve Itch Rev.1.1:

-B+ PSU: can I use 200uF / 350V instead 220uF/450V for C3-C4?
-Heaters PSU: can I use 33uF/16V or 47uF/50V instead 22uF/25V for C8-C9?
-For insterstage cap: can I use 47nF/200V instead 47nF/250V for C4?
-I'm sorry my ignorance, how have to measure 1.36mA & 3.5mA: between the junction & cathode using a 1R or 10R resistor?
-All resistors 1/4W except R2 82K 2W & R10 33K 2W?

 

[Salas]

-350V sounds marginal for mains variations
-Yes
-Marginal
-See Vdrops on R3 & R11 and divide with each one value
-Yes

 

[merlin el mago]

Thanks Salas,

-For instersatge cap could I use Russian FT3 100nF 600V?

OK I will use 220uF 450V for mains caps PSU B+

If don't measure 1.36mA & 3.5mA could I change the resistors accordingly to reach the mA necesary?

 

[Salas]

-Yes if 100nF will not sound too full in big speakers

-OK

No, you measure for ballpark value so to know its about right. Each valve biases differently so you try match valves by seeing those numbers close enough between channels.

 

[merlin el mago]

Thanks for the input Salas

For 6N2PEV can try with different valves but for 6H8C it's a little bit more complicate if supplier can't sell real matched pairs.

 

[merlin el mago]

I believe 6H8C is pin compatible with 6SN7?

 

[Salas]

Same tubes.

 

[merlin el mago]

Are you elevating heaters to 150V?

 

[Salas]

For the top halve of each totem pole only.

 

[merlin el mago]

Thanks Salas

 

[merlin el mago]

Can I measure heater elevated 150V without valves connected or is necessary have the valves connected?

 

[woodturner-fran]

It's ok to power up without valves, but the b+ might be higher due to no load.

 

[merlin el mago]

B+ is 300V, but without valves when measuring heater elevated DMM reads 0V instead 150V, heaters are ok 6,1V

 

[woodturner-fran]

Check the voltage divider resistors and cap that give you the 150v - something not right there I'd say.

 

[merlin el mago]

ok thks Fran

 

[merlin el mago]

Are you sure Frank? without valves?

 

[woodturner-fran]

You should be able to power it all up with no valves installed, just your voltages may be a little higher because there is no load. You won;t be able to check voltages throughout the circuit since you won't have a complete circuit. But you will be able to see your heater and B+ voltages OK.

********Please note that because you have no load, the B+ may take a lot longer to drop to safe levels than normal!!!*********

So you have a B+ of 300V, you have the 2 sets of heaters giving you ~6V. Thats all good.

Now with the power off, check resistance from ground to either side of the 2 resistors that give you the 150V (the 470K-220K in the original heater sch). It seems to me that its likely theres something wrong the the 2 resistors here, or else the connection from the heater to that point?

If it was working correctly, powered up but no valves, you should have:

GND to B+ of 300V
GND to GND of elevated heater of ~150V
GND to + of elevated heater of ~156V
GND to GND of other heater of 0V


Fran

 

[merlin el mago]

I'm doing somwthing wrong, surely I'm tyred, tomorrow I will check again, thanks Frank for support.

Felipe