Single ended MM tube phono amp

[matose]

I jut bought this from eBay and beside the fake caps I don't get if this is a real tube preamp of just a fake one. Apart from the passive components it has onboard: 2 x ZTX384 transistors, 2 x LM317T, 2 x 6J1 tubes.

Can you shed some light if it worth keeping and change the caps and tubes (already bought some Sylvania 6AK5 to replace the chinese tubes) or just return it?

Thanks in advance!

 

[JonSnell Electronic]

Have you looked at the schematic?
LM317 is heater regulator, my guess.
ZTX384 is obsolete.
6J1 similar to EF95. Single pentode, IF amplifier. Possibly low noise.
If it was cheap, does it work? If it does what you want it to, keep it if not send it back.

 

[Merlinb]

These Chinese kits usually use the tube as a cathode follower output stage. There are some surface mount transistors on there too.
My guess would be ZTX transistor input input followed by a transistor-based RIAA, followed by 6J1 output 'driver'.
One LM317 will be for the heater supply, the other, maybe to regulate the rail voltage?

 

[matose]

I think each 6J1 has its own LM317 heater supply. I don't have the schematics unfortunately. Any point in replacing the ZTX? With what?

 

[kevinkr]

Why would you replace the ztx? Presumably provided they are the real deal they function as the designer of the board intended.

Try first and see what you've got.

 

[matose]

Because the ZTX384 is an old and outdated part 🙂

 

[BinaryMike]

I see only two plastic film caps on the board, and two ceramic caps. It seems unlikely that anyone could make a good RIAA equalization circuit with those capacitors alone.

 

[Merlinb]

Because the ZTX384 is an old and outdated part

Not as outdated as the tube! 😱

 

[soulmerchant]

if it doesn't sound good with Chinese tubes, then NOS sylvanias won't help it.

 

[ViperZ]

Have you looked at the schematic?
LM317 is heater regulator, my guess.
ZTX384 is obsolete.
6J1 similar to EF95. Single pentode, IF amplifier. Possibly low noise.
If it was cheap, does it work? If it does what you want it to, keep it if not send it back.

Sorry to revive an old thread, but is there a schematic available for this "Douk Audio" phono?
Someone gave me theirs to play with, and it's humming loud. I quickly checked pin to pin on LM317 (one per channel), and I'm getting different readings voltage-wise and impedance-wise.

Thank you.