|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
65.6.248.210
In Reply to: GE 6CA7 - Can't bias tube low enough posted by Capt. Z on April 12, 2007 at 04:56:47:
Hi:
Are these the large bottle 6CA7's, about the size of a 6L6GC or larger?If so, and the amp was designed for the skinny bottle 6CA7/EL34 type, that might explain it.
The large bottle type needs more negative bias then the EL34. In some amps, you can change a resistor in the bias circuit to change the operating range of the bias adjustment.
Follow Ups:
"The large bottle type needs more negative bias then the EL34."I'm not sure I agree. The tube specs don't indicate that should be the case. And my experience has shown that the variance from batch to batch and tube to tube of either type (6CA7 or EL34) is the biggest difference in bias required. I have plenty of hotter EL34s that need more negative voltage than the cooler 6CA7s.
Hi Jim:I agree, the tube specs don't indicate that. But in my experience, generally, the 6CA7's have been hotter, requiring more neg bias than EL34's, regardless of brand or batch.
Please correct me if I'm wrong, but is not the 6CA7 a beam power tube, and the EL34 a true pentode?
Perhaps that would explain the difference?
The GE 6CA7 are shorter and fatter than the EL34, they are also called "Fat boys".
This post is made possible by the generous support of people like you and our sponsors: