Buffalo DAC output stage

[jmanalo]

Nick,

Thanks for the good design. I finally installed the chokes that you recommended and it sounds good. I have few more questions for you.
Now I'm getting 190V to my B+ after I installed the choke, do I have to reduce it to 170V? What are the consequences if I leave it at 190V?
Thanks,

Joe

[Nick]

No, 190v is close enough, the 6n6p is working a little harder, but still well within its limits. If anything the higher current that results will improve things. Remember to balance the current with the new voltage if its getting close to a finished circuit.

[jmanalo]

Hi Nick,

I need help please...
My right channel tube keeps on going (open) bad.
I just installed and zero'd the new 6n6p more than a month ago, the right tube turns (open) bad, then I replaced it couple of days ago, after one day of used, it turns bad again. What could be the problem?
Is this a bad tube? Coincidence that happened on the same channel twice?

My measured voltage in ref. to gnd before the second problem:
with tube plug in, both channel reads almost identical.
Pin 1. 187V
2. 1.74
3. 7.2
4. 6.3
5. 0
6. 188
7. 1.74
8. 7.65
9. 0

I removed the tube and measure the socket, the voltages were similar on both channel and compared with tube, except for the few pins.

the only difference are:

Pin 1. 218V
3. 0V
6. 218
8. 0V

Thanks,

Joe

[Nick]

When you say it goes bad, what fails, is it the heater that fails?

[jmanalo]

Nick,

The cathode (pin3 and 8 ) measured 0V. I assumed this is the problem?

Thanks,

Joe

[jmanalo]

Nick,

I've checked those testpoint resistors that is connected to the cathode, all of them are OK, maybe the tube are just bad. I put another tube and it's working fiine again. Thanks for your help.

Joe

[jmanalo]

Hi Nick,

Can I increase the value of 50R pot to 60R? The last time I tried to zero the TP1 and TP2, on one tube it only goes to 0.063V.

Thanks,

Joe

[Nick]

Yes, you can, but may be worth considering another 6n6p, some I found are harder to get into balance than others.

[jmanalo]

Hi Nick,

Can I try this Finemet transformer in your circuit on the start of this thread in place of Sowter 8650? If I can, what are the necessary changes do I need to do?
Here is the link to Finemet at thread #180: http://www.diyaudio.com/forums/twisted- ... rs-18.html

Here are some info about the Finemet transformer.
ESS9018 transformers is made by Mr. Yasuo Suzuki - a “typicalâ€￾ Japanese audiophile. Primary DC resistance is 14 Ohms, and secondary resistance is 16 Ohms, and the turn´s ratio is 1+1:1+1. The transformers can be had with black urushi coating that is supposed to dampen against microphony.

Information about FINEMET can be found here http://www.hitachi-metals.co.jp/prod/pr ... -fm9-e.pdf.

Thanks,

Joe

[Nick]

No, that looks like its designed to go between the buffalo and any following stage, in this case the 6n6p grids.