Tubes Asylum

Questions about tubes and gear that glows. FAQ

Use this form to submit comments directly to the Asylum moderators for this forum. We're particularly interested in truly outstanding posts that might be added to our FAQs.
You may also use this form to provide feedback or to call attention to messages that may be in violation of our content rules.

You must login to use this feature.

Inmate Login

By default, logging in will set a session cookie that disappears when you close your browser. Clicking on the 'Remember my Moniker & Password' below will cause a permanent 'Login Cookie' to be set.

Moniker/Username: The Name that you picked or by default, your email. Forgot Moniker?	Examples "Rapper", "Bob W", "joe@aol.com".
Password:	Forgot Password?
	Remember my Moniker & Password ( What's this?)

If you don't have an Asylum Account, you can create one by clicking Here.

Our privacy policy can be reviewed by clicking Here.

Inmate Comments

From:
Your Email:
Subject:

Message Comments

Original Message

I get no music out of mynewly built amp

Posted by DAK on October 17, 2016 at 19:12:52:
I just built a SE kt90 amp with 6j5 driver tube. The amp uses fixed bias. I guess i have 2 problems. first my bias voltage is not able to go low enough to get the power tubes to their proper cathode current. The bias circuit takes -60v to 4.7k resistor to 50K pot which is grounded with a 5k resistor. The wiper is connected thru a 13k resistor which goes to the grid of the power tube. This arrangement yields between -30 to -45 volts of bias voltage. I need to reduce the negative voltage to raise the current of the power tube. so, i am not sure which resistor/s to change to have a more effective bias voltage.
The next part of my problem is that i believe the plate voltage of the 6j5 tube is too low at 60vdc. The B+ to the plate 100k plate load resistors is 250v. I am following the RH universal amp version 2. I have built this amp many times now with mostly 6sl7 driver tube. And also a version with switchable 6sn7 and 6sl7 driver tube. I am following the exact same circuit as the switchable 6sl7 to 6sn7 except using the 6j5, which is 1/2 of a 6sn7. Not sure what is going unless it has to do with the fixed bias .
Well, i kind of ran out of ideas of what to do here so any suggestions would be most appreciated. cheers, Dak