"I think the 6AS7 is shot."
The dreaded cathode stripping.....I feel your pain.
Please read and like tubecad.com.
tubecad.com/2020/05/blog0504.htm
The dreaded cathode stripping.....I feel your pain.
Please read and like tubecad.com.
tubecad.com/2020/05/blog0504.htm
As you noticed in my response #16 there is a POSITIVE voltage difference between the grid and the cathode of the output tube ( I would expect a NEGATIVE voltage).
What are the voltages of the properly working channel? I understood from the thread starter that only 1 channel was having this problem??
What are the voltages of the properly working channel? I understood from the thread starter that only 1 channel was having this problem??
Joe look at the attachment in post #15. There are two schematics with voltages - one for the working channel and the other for the not working channel. It is only one channel that's out.
Sorry, but I only see 1 schematic diagram voltages. Can you publish the "good" channel voltages? This gives me an idea what the designer was aiming at.
Ahhh! No I did not scroll down! Wasn't aware of this. Those other figures look normal to me. Have to study them tomorrow, but
perhaps the other members can now conclude what is happening here.
perhaps the other members can now conclude what is happening here.
Probably the tube has failed with some kind of short from grid to cathode because they didn't used that protection diode described above in the tubecad article and of course known from a long time ... It should be added after you buy another 6080 tube
He needs to look at this schematic in particular:
https://tubecad.com/2020/05/25/CF OTL/CF OTL 6SN7 6AS7.png
This small change will save his tubes during turn-on.
"This small change will save his tubes during turn-on."
See my response #14
See my response #14
Yup. That diode works in these circuits - It's especially needed if you do not have a slow start-up.
@JoeAlders Yes got the new tubes and plugged them in and that solved the dead channel problem. Got a Sylvania 6AS7 and also an RCA version. I also replaced the stock China 6SN7 with a JJ even tho the stock tube works. I also installed those two diodes to protect the 6AS7 on power up and created an artificial center tap for the filaments with two 100 ohm resistors and connected their junction to a higher dc voltage through a voltage divider to eliminate the filament hum. The manufacturer could have done all that for less than a dollar but I'm happy cuz I only paid a bit over $200 for the Darkvoice. Also got Beyerdynamic DT880 600 ohm headphones which are a good match. They sound better with this amp than the Grado SR80 phones I've had for about 30 years.