Valve Itch phono

[merlin el mago]

Aprox. 26,6 ohm input & 260 ohm output

Partridge 977 measurements.

 

[Salas]

Its OK for the DL-103R bcs its 18-19 Ohm for real so the 977 primary loading is very near.
59dB total will give 220mV. Not for a buffer preamp.

BTW the Jensen JT44 at 10KHZ square before and after Zobel termination on its secondary.

 

[Salas]

All SUTs should be checked with square waves for best termination loading. Others will need RC others just the best R load.

 

[merlin el mago]

Jensen input impedance typical 430 ohms, do you use 6K81 + 200pF accross the secondary?
BTW I have a quote from Jensen JT-44K-DX 1:10 Step-up Transformers $233.47 USD including shipping but first I nedd to sell my Partridge.

 

[Salas]

That price is for a pair or each?

6K8 + 200pF dulled the leading edge too much for me. I ended at 100pF polystyrene for the picture I posted. But this is a test with longer cables so its possible to be optimized at 130-150pF in a build. And there is ear check in the end for each one's cart and phono.

 

[merlin el mago]

It's for a pair, how much did you payed?

 

[Salas]

50$ each if I remember well. They were navy pull outs as good as new.

 

[merlin el mago]

You were lucky.

 

[merlin el mago]

How to check if the Itch ampifies 43dBs?

Wich kind of generator I need? I guess I can't use my LAG120A...

Salas YHPM

 

[Salas]

You can. Its 600 Ohm like an MM cart.
Measure 200mV RMS 1kHZ on its output at 0 attenuation with the DMM on AC. Then select 40dB attenuation. Feed it straight to Itch without SUT. You should get about 280mV RMS on Itch's output for 43dB.

 

[merlin el mago]

Super I'll do and let you know, thks for help.

 

[merlin el mago]

You can. Its 600 Ohm like an MM cart.
Measure 200mV RMS 1kHZ on its output at 0 attenuation with the DMM on AC. Then select 40dB attenuation. Feed it straight to Itch without SUT. You should get about 280mV RMS on Itch's output for 43dB.

Used 192mVRMS
Right channel 247mVRMS
Left channel 184mVRMS

 

[Salas]

Right channel is within experimental error near gain spec.
On left channel find higher mu valves samples until near match to right channel.
You need 2dB better matched mu between their sections.

 

[stajo]

I have some boxes of 6N2P-EV, and even some military grade OC's that I can measure up for you if you get stuck Merlin

 

[merlin el mago]

Thanks stajo.

Salas Voskhov marked by the seller Ia 2-2.5mA & S 2-2.2mA/V, wich value I need?

 

[Salas]

Ask for the more S at a given Ia (more current gain) and best match between the two internal sections for S.

 

[Salas]

Also swap the 6SN7s to see your total output again. Those are multipliers and can be adding mismatch too.

 

[merlin el mago]

Changed the other Voskhod for another standard, now Left channel 222 mV RMS, I will try swapping the 1578.

 

[merlin el mago]

Swapping the 1578

Left channel 242 V RMS
Right channel 274 V RMS

 

[Salas]

Much better (mV). Try more 6N8S if you got.