Russian Tube Preamp, No Return, Here I go again

Sergey's response, he says NO to using substitute for 6N4P

"

Dear Elliott!

 

Suppose nothing was shaken during transportation and the preamplifier is in good working order.

Why there may be noise:

- bad connecting cable. This happens. I have a couple of factory cables that are noisy and made by myself - no noise.

- incompatibility of components, low input impedance of the power amplifier. A similar case was with one of the AT-11s sold in Russia. After connecting to another power amplifier - thanks for the sound.

- it is possible that the power supply network in your house is phoning. You have an abundance of technology there, so it is quite possible.

 

About tubes. They are very unlikely to cause noise, provided they are properly installed in their nests.

12AY7 and 6072 - CANNOT be installed instead of 6N4P.

 

6922, E88CC 6DJ8 - can be installed instead of 6N23P.

 

But it can also be assumed that some kind of contact has departed during transportation. If the noise is low frequency, maybe something has fallen off (or on the verge of it) in the power circuits.

 

What a shame I can't look at the preamplifier. As a designer, I am very worried about my work. How so - 4 pieces sent to different countries sound perfect, but with yours - such a disaster ...

Best regards,

Sergey"

I tried again: changed power cord; changed the 12ax7; found/tightened another partially loose screw on the phono card; moved to my office system; existing TT and direct to existing amp.

Worse, it now makes thumps during it's 'soft start' period, then the same noises. I'm done.

Somewhere much earlier in this thread, I got the impression that your preamp uses the 6N23, which is replaceable by the 6922. I don’t know about the 6N4P, without doing more research on it. Am I losing my mind, or did you once mention the 6N23? Yes, 6072 and 12AY7 are essentially different names for the exact same tube. I will look to see whether there is any evidence that the 6072 can replace the 6N4P.

Here is a useful website: https://www.radiomuseum.org/tubes/tube_6n4p.html
From that page, you can also look up the 12AY7 and 6072.  To my eyes, the latter two should be cross-compatible with the 6N4P. (Be careful if you do your own research, because apparently there is also a Chinese 6N4P, and it is not the same as this Russian 6N4P.)  The caveat is the filament voltage.  For the 6072/12AY7, they can be run on either 6V or 12V filament supplies.  I am not sure from the information on the given website that the same is true of the 6N4P, which may require 6V.  Still, I don't see why he says you cannot use the 6072/12AY7.  The pin connections to plates, grids, and cathodes are identical to those of the 6N4P, and the electrical parameters are close enough. Ask the seller.

Thanks but I'm done trying. I now think the phono board got damaged in shipment somehow, what a shame. 

See my newest enthusiasm in this new thread

https://forum.audiogon.com/discussions/luxman-lx33-integrated-tube-amp-yeah-nay

about this LX33.

https://www.ebay.com/itm/154051395889?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=533...