Valve Itch phono

[merlin el mago]

Swapping the standard 6N2PEV

Left channel 217 V RMS
Right channel 245 V RMS

 

[Salas]

That is just 1dB difference. As the one before.
Now to see about experimental error and changes due to gear, go to 500mV at 0 attenuation so the DMM can catch it better, let it there, then go -40dB (be sure there is no center trim button on the attenuator out of cal position). And measure again.

 

[merlin el mago]

502mV 0 attenuation, measured with -40dB attenuation

Left channel 565mV
Right channel 632mV

 

[Salas]

42dB max and 0.97dB difference. When you will have more tubes maybe you will strike a 0.5dB combination or better.

Swapping the 1578

Left channel 242 V RMS
Right channel 274 V RMS

At the above combination you had hit the 43dB max and ~1dB difference.

 

[Salas]

That is with 192mV at 0dB attenuation as signal from your Leader gen. After -40dB attenuation for Itch input signal, 255-275mV on Itch's output will mean 43dB max gain right on spec and 0.5dB max tolerance.

 

[merlin el mago]

502mV 0 attenuation, measured with -40dB attenuation

Left channel 565mV
Right channel 632mV

That is with 192mV at 0dB attenuation as signal from your Leader gen. After -40dB attenuation for Itch input signal, 255-275mV on Itch's output will mean 43dB max gain right on spec and 0.5dB max tolerance.

Do you refer to this post Salas?

 

[Salas]

I refer to the combination where you hit 274 using 192 at 0 attn. If you used 502 with that valves combination it will still be the same dB.

 

[merlin el mago]

I refer to the combination where you hit 274 using 192 at 0 attn. If you used 502 with that valves combination it will still be the same dB.

Yes it's the same tube combination only changes 502mV in place of 192mV. I have more 1578 can I try the new tubes, wich position V4 elevated 1578?

 

[Salas]

See post #146

 

[stajo]

What kind of 6SN7 are you using Merlin?

 

[merlin el mago]

6H8C 1578 hole plate metal base

 

[merlin el mago]

See post #146

Oooooops Salas conected heater ground to elevated tubes

 

[Salas]

There are two tubes in each stage between channels. Each one common functions as upper half CCS with elevated heaters while the other as lower half for signal with grounded heaters. They form the Mu follower stages.

 

[merlin el mago]

I damaged the tube?

Can be the reason to affect the sound or gain?

 

[stajo]

6H8C 1578 hole plate metal base

I like those. Are they measured?

 

[merlin el mago]

I like those. Are they measured?

I bought matched, how can I measure?

 

[Salas]

I damaged the tube?

Can be the reason to affect the sound or gain?

Don't know without real examination. If you had followed the PSU schematic you could not had it wired wrong for heaters.

 

[stajo]

I bought matched, how can I measure?

Whithout tube tester, sinus in on grid sinus out on anode in circuit

 

[merlin el mago]

Yes I know my fault sorry, I guess tubes are OK or gain measurements results not OK, what do you think?

 

[merlin el mago]

Whithout tube tester, sinus in on grid sinus out on anode in circuit

What have to look for: the same gain?