Want help - RCA Tube Manual RIAA Phono Stage

[brucetassin]

Academia50,

Here is a circuit you may find interesting.

Bruce

 

[academia50]

Hi brucetassin


I had not seen this thread .....
Sorry for not responding sooner!
I have put on hold the project because I am dedicated to changing background with boxes.

http://www.diyaudio.com/forums/search.php?searchid=10218406


But I liked it, is exactly what I need.

What voltage would be the correct plates for straight right load of this circuit ?

Thanks and regards !

 

[varmax]

Ok this is an old thread but i 'm bringing it up as i already started building the Eli's version with the mosfet follower.Ihave one question regarding the mosfet ZVN0545A.
Can i use sustitute for this?
Let's say the IRF840 which is rated at 500v is it ok to use it?

 

[jazbo8]

They are two very different devices...

 

[bandol83]

Hi,

I would suggest STQ3N45K3 from ST, it is not the same pinout however but for a small TO92 it is much more powerful than the ZVN0545 (3W instead of 0.7W).
I have used it in my RIAA preamp with good result... You can find more info here ; Merlin RIAA Preamp

Regards
Marc

 

[varmax]

Thanks very much for your answers!
i guess i need to order then.
I'' look for the STQ3N45K3

 

[Merlinb]

I have one question regarding the mosfet ZVN0545A.
Can i use sustitute for this?
Let's say the IRF840 which is rated at 500v is it ok to use it?

Yes, most any MOSFET will work OK in that position (assuming you get the pinout correct of course). It would be a good idea to add a 10V to 15V zener diode between gate and source though, for protection (cathode towards the gate).

 

[Eli Duttman]

Merlin is correct about adding a protective Zener diode, to deal with turn on surges.

Any "N" channel enhancement mode MOSFET whose reverse transfer capacitance is low and stable will work. The reasons for the requirement are: the 'X7 triode is a wimp and avoidance of HF info. loss.

 

[LJT]

Eli's version is using a MOSFET for line buffering. Other variants use a cathode follower(for example Morgan Jones and the schematics on Valve Wizard site).

What would be the advantage / disadvantage of either versjon (technical and subjective).

 

[varmax]

Best wishes for the new year!
I ve just finished the Eli's version preamp and also build the psu that he suggest...250v x2 and 12v for the heater. Everything seems ok but cannot get the fillaments glow.but i do get 11.75v on pin 4 and 5. I also get 245v on pin 1 on both sockets without tubes,but with tubes in place i get only 12 volt.It' really confusing.At least the heaters should have glown as i have the voltage on pins 4,5. I use 2 12ax7 tubes.Any ideas on what it might be the problem are welcomed!

 

[DUG]

Best wishes for the new year!
I ve just finished the Eli's version preamp and also build the psu that he suggest...<snip>

Possible pin 1 vs pin 9 reversal on "top view" vs "bottom view"

Been there, done that.

 

[bandol83]

Me too

 

[varmax]

Possible pin 1 vs pin 9 reversal on "top view" vs "bottom view"

Been there, done that.

ffffffff...... now,me too!!!
Thanks guys!

 

[varmax]

one last question,
I measure the output for both channels (from output rca jack) and when i plug it in, it starts from 150v until slowly give me around 30 volts.
something wrong here?

 

[varmax]

I replaced the 4,7 uf which by my mistake were rated @ 63 instead of 630 v.Now the dc voltage is almost 0 or milivolts but stil when i plug it it shows 150 vdc for about 10 seconds before goes to zero.Why is that?.Is these blocking capacitors(4,7 uf and 0.47uf) there for that reason,to not let the dc pass?

 

[DUG]

Should be rated at supply voltage.

Initial 150V to final 0V shows output cap charging...normal