6DJ8/ECC88-SRPP Tube Preamplifier

[merlin el mago]

For 6.3V you connect one side of power to pins 4 & 5, the other side to pin 9.

I you have 6.3V on pins 4 & 5, then that's why your circuit does not work. The filaments are not running at the correct voltage.

So pins 4 & 5 connected togheter to +6.3V & to pin 9 GND? that's make sense because heaters never lit.

 

[scott17]

So pins 4 & 5 connected togheter to +6.3V & to pin 9 GND? that's make sense because heaters never lit.

Yes.

 

[merlin el mago]

Thanks for help Scott, just checked the EI manufacturer website of my ECC81 & you are right 9-(4+5) for 6.3V 300mA.

 

[merlin el mago]

B+ 280V

I have tube left channel:
between upper cathode pin 3 & 560R 167.5V
between 560R & 33K 163.4V
between 33k/15nF anode pin 6 96.5V

I have tube right channel:
between upper cathode pin 3 & 560R 168V
between 560R & 33K 166V
between 33k/15nF anode pin 6 100.1V

Seems that now are OK

 

[revintage]

Yep

 

[merlin el mago]

Now I'm wiring the volume pot, output caps, etc. Surely tomorrow will hear to see how goes, next monday comes my friend with his Aleph X100.

 

[yd1cvj]

Hi merlin,
Hope it goes well. Have you finished and tried? i will preamp make based on your scheme.

 

[merlin el mago]

Yes I have finished, I only need to connect in my system but is full balanced so I need to change the interconnects to try it.

 

[yd1cvj]

Hi Merlin,
Apreciate for your up date.

 

[merlin el mago]

I was very busy with other project, I will let you know as soon as possible.

 

[merlin el mago]

Connected the preamp but sounded wrong and woofers like having DC also it was smelling to burned so I disconnected.

New measurements:

B+ 280V in both anode channels

I have tube left channel:
between upper cathode pin 3 & 560R = 169.5V
between 560R & 33K = 130V
between 33k/15nF anode pin 6 = 47V

I have tube right channel:
between upper cathode pin 3 & 560R = 173.2V
between 560R & 33K = 167V
between 33k/15nF anode pin 6 = 27V

Pic with big sinu. is right channel small sinu. is left channel both aren't with the same scope settings, scope setting are to see the best sinu. possible.

 

[merlin el mago]

Oooops forgot to connect the GND signal to GND chassis now the measurements are:

B+ 280V in both anode channels

I have tube left channel:
between upper cathode pin 3 & 560R = 170V
between 560R & 33K = 165.8V
between 33k/15nF anode pin 6 = 96.2V

I have tube right channel:
between upper cathode pin 3 & 560R = 174V
between 560R & 33K = 169.8V
between 33k/15nF anode pin 6 = 102.1V

I have in both channels a nice sinu.

 

[formula 22]

Hi guys!
If you take out the capacitor of 150uF for how to reduce the gain and what will be another change in the preamplifiers?
thank you!

 

[merlin el mago]

Hi guys!
If you take out the capacitor of 150uF for how to reduce the gain and what will be another change in the preamplifiers?
thank you!

 

[soulmerchant]

did you ever try the cheap red diode (instead of resistor+cathode by-pass cap) that Sy suggested early on?

I wonder if anyone has experienced this with a mu-follower...

 

[merlin el mago]

Sounds nice but with hum, I followed all advices of Auido Component Grounding and Interconnection by David Davenport except the safety ground and chassis connected to the system star ground trought a Safety Loop Breaker Circuit, any other idea to fix the hum issue?

 

[merlin el mago]

did you ever try the cheap red diode (instead of resistor+cathode by-pass cap) that Sy suggested early on?

I wonder if anyone has experienced this with a mu-follower...

I used with good succes in other tube preamp, now first I want to get ride the hum and after I will try and let you know.

 

[merlin el mago]

Hi merlin,
Hope it goes well. Have you finished and tried? i will preamp make based on your scheme.

Hi Merlin,
Apreciate for your up date.

Hi yd1cvj,

ECC-81 mu-follower I fixed the hum issue of my ECC-81 mu-follower with proper grounding techniques, I used Salas regulator for B+ SSHV2, sounds very very good: ultra-transparent, ultra-fast, not seems caractheristic/colored tube sound, plenty of power ideal for low power amps, tested with Pass Aleph-X 100W fully balanced, really you need to spend a lot of money to get better sound with other commercial stuff, higly recommended.

Now I'm making the mu-follower with two 6SN7 see my other thread http://www.diyaudio.com/forums/tubes-valves/216948-6sn7-6n8s-preamp-suggestions.html

 

[yd1cvj]

Hi yd1cvj,

ECC-81 mu-follower I fixed the hum issue of my ECC-81 mu-follower with proper grounding techniques, I used Salas regulator for B+ SSHV2, sounds very very good: ultra-transparent, ultra-fast, not seems caractheristic/colored tube sound, plenty of power ideal for low power amps, tested with Pass Aleph-X 100W fully balanced, really you need to spend a lot of money to get better sound with other commercial stuff, higly recommended.

Now I'm making the mu-follower with two 6SN7 see my other thread http://www.diyaudio.com/forums/tubes-valves/216948-6sn7-6n8s-preamp-suggestions.html

really you need to spend a lot of money to get better sound with other commercial stuff,

Yes . Thank's for sharing.

 

[merlin el mago]

Now I upgraded with AZ1 graetz rectification and all MKP PSU caps, for my needs I use a voltage divider (I have 75 W RMS Class A mono-blocks) so don't need all the gain, I have now aprox 26dBs & sounds still better, less dull, still fast & clear but so far more natural and no fatigue sound.

Worth a try.