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RE: Scott 222B, setting bias,etc. questions

Posted by dadbar (A) on March 19, 2011 at 20:19:54

In Reply to: Scott 222B, setting bias,etc. questions posted by locum on March 19, 2011 at 12:43:13:

The 222B is cathode biased so it does not have a selenium rectifier. The 4 12AX7 heaters are all in series- if one tube heater fails they will all go out simultaneously. More likely you have a dirty tube socket which is why they're not heating up (note that if you are using the EH 12AX7LPS these tubes have hidden heaters and you will not see any glow from these). Clean and retension the sockets first (pull the tubes in and out a bunch of times)...probably one is not up to snuff.

The 4 12AX7's tube heaters serve as part of the cathode bias resistor so you may need to get the sockets cleaned and a good quad established prior to fine tuning your bias. That's why your service maven is technically correct...

Good luck....

• http://hhscott.com/pdf/fs/222B-C1.JPG   (Open in New Window)

Edits: 03/19/11 03/19/11

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