Phono Stage tube PCF802 from VLAD ~ any info?

[niclaspa]

Vlad's phono stage use DC to heat the tubes.  That is advisable when dealing with the small signals that comes out of a cartridge.  For your buffer, that is not necessary.  I think that the best choice is to use AC to heat the ECC82.  It is much simpler.  The signal is fairly big and you will have no issues with hum, if you take a little bit of care when wiring.  Have a quick look here: https://www.diyaudio.com/community/threads/heater-wiring-the-good-the-bad-and-the-ugly.211731/ 

[Tomcat1969]

Vlad's phono stage use DC to heat the tubes.  That is advisable when dealing with the small signals that comes out of a cartridge.  For your buffer, that is not necessary.  I think that the best choice is to use AC to heat the ECC82.  It is much simpler.  The signal is fairly big and you will have no issues with hum, if you take a little bit of care when wiring.  Have a quick look here: https://www.diyaudio.com/community/threads/heater-wiring-the-good-the-bad-and-the-ugly.211731/ 

Excellent, thanks again.

[wenig watt]

Thank you very much Andreas and Niclas!

Best regards

Arndt

[vlad1980]

I haven't entered this topic for a while because I was away on vacation for a few weeks. I see that there is a lot of fun with this kit and that makes me happy.

I made a new version of the board  with input capacitor and resistor selector as follows:
-   120p and 240p for capacitor
-   47k and 100k for resistance.

Looks like this:

[Tomcat1969]

Its a great kit Vlad. And lots of fun. 

Niclas would you mind looking over my buffer build?

[niclaspa]

Niclas would you mind looking over my buffer build?

Of course, show us some good pictures.   

[Tomcat1969]

Of course, show us some good pictures.   

Thats brilliant Niclas. Thank you so much. 

I'll post some later later today.

[Tomcat1969]

Ok, here it is. Be brutal. I like criteque from knowledgeable people. There are bound to mistakes.






Red wire-signal
Black wire-B+
Green going to ground.
B+ rail at the top, ground at the bottom

2x100r are missing and I'm waiting for them to be posted alongwith fibre washers.

Obviously I'm not finished but I didn't want to proceed much more without seeking some advice.

Many thanks.

[Tomcat1969]

[niclaspa]

I can see only one thing that you should change.  The 1 k resistor attached to the grid of the triode is there to stop the tube from oscillating.  The best thing is to solder it directly to the tube socket:



More to read about this here: http://www.valvewizard.co.uk/gridstopper.html

[Tomcat1969]

I can see only one thing that you should change.  The 1 k resistor attached to the grid of the triode is there to stop the tube from oscillating.  The best thing is to solder it directly to the tube socket:



More to read about this here: http://www.valvewizard.co.uk/gridstopper.html

Ok, Niclas. Good news for me. I will change the 1k and have read about the gridstopper.

I'm very happy. Thank you again.

[Tomcat1969]

I've got the heater elevation circuit built. I will transfer it to a metal base I think. I thought the acrylic would be good for insulating the circuit but then I thought about heat.




I have also added a cartridge loading switch. 10r, 100r, 1k and 47k. And space for two more values.

[niclaspa]

Acrylic is fine.  It doesn't get very hot in this amplifier.  But, it is not needed at all.  The solder tags provide insulation.

[Tomcat1969]

So I've built the buffer and the heater elevation circuit. I've tried it out and got no sound.

All the valves were glowing and all seemed well, but after 2-3 minutes the fuse blew.

When I looked over the buffer circuit I saw the the 18k resistors had been roasted.

I'm not sure if I have tapped into the phono signal at the correct point on the PCB.

[niclaspa]

The fact that the fuse blew makes me think that something is wrong with the wiring.  Could you take some pictures and post here?  Also, pictures where you have tapped into the PCB.