Valve Itch phono

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#3,061
Haven't listened to the radio on various iterations of this so it isn't inherent. It is some detail in your build. For MM you can put 100R grid stopper as a quick measure because such cartridges have higher impedance and it will not affect the noise significantly. There are ferrite beads to try as well. Better/shielded small signal's cabling practice i.e. narrower loop areas of it and tighter construction in the build itself should be thought of and revisited. A grounded metal box is good to transfer the build to, or dress the wooden box's inside with grounded MuMetal shielding, but if its a sensitive tubes issue some locking metal cap shield with compatible base is effective.
 
#3,066
Yea I have also used that on 12QAX7-like tubes for riaa inputs, usually helps. Good if the metal hugs the glass so it transports heat rather then prohibiting airflow. I have a box of those various caps somewhere. And a soldered wire as direct to earth as possible is good.
 
#3,067
Choke questions

Hi
I have a couple of orphan chokes and thought I could use them in an Itch. I plugged some values into PSUD and came up with a supply that 'hopefully' suits a SSHV2 regulated version of Rev1.2, to be housed in a separate box. The power transformer is a Hammond 370BX putting out about 300v unloaded on local mains voltage. The heater transformers are Hammond toroids (1182K9).

Does this look like it will work?

Thanks

Keith
 

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#3,073
I don't know... 10% (?). V2 & V4 sections are the main consumers. Try two different tubes there and measure voltage drop across any resistor in their way (R9 R10 R11) to derive mA when dividing Vdrop by the resistor's value. That will give you an idea of mA bias difference across your own tubes.
 
#3,075
Didn't have in the past but it recently developed? If so I would start from tubes swap or screening or moving away if other gear transformer was introduced nearby and the hum went up or undo some sensitive modification
 
#3,077
If the contacts are clean inside them and they achieve good mechanical lock I would not think that the choice of bases can be a factor for background noise. Adapter maybe can expose more if its barrel is not grounded, but a swap from 7N7 back to 6SN7 direct would tell.
 
#3,079
Don't know, haven't used such high quality sockets. Beyond the good insulation material they seem to have very nice machined copper gold plated contacts also and that alone can be a plus when combined with well cleaned and chemicals treated tube pins (Cramolin/Deoxit).
 
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