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

Re: Any thoughts on my MC275's snap, crakle and pop?

Posted by Sector-7G on November 3, 2002 at 12:21:04:
Hey-Hey!!!,
I have a 275 behind me that did what you are describing. Sound form one channel, a bit like driping water, a bit of a sizzling sond to it. Tried swithing all the tubes to no avail. I found a bad cathode bypass cap on the 12AX7, something like a 3volt 100 uF 'lytic. Try measuring the resistance of these caps, as the voltage of an ohm meter is comparable to the actual woring voltage you might see the screwy behaviour. My HP multimeter would not settle down to a range on the bad one like it did with the good one. The 12 uF 250 V 'lytic coupling caps from the cathodes of the 12AT7 to the grid of the power tubes also failed on the other 275 I have. Suspect all 'lytics is the short story.
Short experiment, un-solder the bypass cap from the bad channel's 12AX7 cathode, less gain is all that will happen, and if it's bad you'll have your answer.
BTW, the 12AT7's section to section match is a bit critical for it controlls the actual grid voltage of the power tubes, if you have slightly mismatched power tubes and 12AT7's you can measure and match for better performance. just measure votlage at the power tube's cathodes after you measure the DCR of the cathode winding to determine current, Mc spec is .6 v
regards,
Douglas