Vintage RIAA Phono 12ay7 Circuit

[charly chile]

Vintage RIAA Phono 12ay7 Circuit.

Hi guys,
A friend gave me 2 of these vintage boards.
I want to power them to see how they sound.
Each board use two 12ay7 tubes.
today I finished the reverse engineering and I was able to draw the circuit.
But... I am still not sure about how to use this or what topology exactly it is.

Someone feels like taking a look and providing some clues about input, outputs?

 

[charly chile]

Most important thing to me is to understand how to connect this board.
I already have an old Magnavox 12ax7 EL84 SEP amplifier, and I would like to use its Power supply for the V+ and filament voltages.

Not sure why I have to inputs and two outputs here...


Cheers...

 

[charly chile]

I have translated the circuit into something more readable.
I will put the values of components later.

still looks to me loke the two circuits have to be connected in cascade?
Is this a RIAA circuit?
What would be the voltages for the power supply?

 

[rayma]

looks to me loke the two circuits have to be connected in cascade? Is this a RIAA circuit?
What would be the voltages for the power supply?

As it stands, this is not an RIAA circuit. Maybe a tone control or other circuit goes in between the two.
The grid to ground resistors are missing.

 

[charly chile]

Ho, I see, that is bad.
My ideal would be a Class A, MM non feedback RIAA preamplifier.
I guess I could buy a board of a clone Ear834 and assemble arround that...

I am ignorant about tube amplifiers and RIAA.
But the left circuit seems to have some tone control and NFB?
the right circuit is just an amplifier?

p.s. thank for the grid resistance tip

 

[rayma]

My ideal would be a Class A, MM non feedback RIAA preamplifier.

Just use a passive network between the stages, and remove the output to input feedback RC parts.
http://www.diyaudio.com/forums/tubes-valves/278833-rca-tube-preamplifier-help.html