|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
141.239.172.248
In Reply to: RE: I call BS posted by Palustris on August 27, 2015 at 13:50:43
It just occurred to me that the 5755 is a similar to the 12ax7 with a amplification factor of 100. I checked the pin out and it is as you described. The use of the small PCB reassigns the pins to the ax7 pinout. Western Electric made some 5755 maybe he has a big stash?? But cynical me wonders if it could be the Raytheon 5755 which are quite cheap. It would explain the mumbo jumbo as way to confuse the buyer. Caveat Emptor, Dak
Follow Ups:
The 5755! That's the one I was trying to remember; it's not in my GE 'Essential Characteristics' tube manual which is why I didn't find the base listed. Yes, these were going for a dollar or so each in cases of a thousand, although now the price has risen some. The little adapter PC boards are even available on epay; the exact same ones used in these "12AX7-HD" tubes.
In the end though they are NOT a replacement for a 12AX7 since they have only 40% of the transconductance of a 12AX7 which is already a wimpy tube and almost twice the plate resistance. That means much more noise and much less ability to drive a following stage. I would steer well clear of these tubes for audio.
Has to be the 5755, likely Raytheon manufacture as said. I believe that most of the Western Electric manufactured 420A's were clear tops, actually all clear glass, appearing to not have a getter at all. IIRC, they used some sort of powder as getter material.
I know that W.E. subcontracted companies to manufacture their types, so technically, these could really be "W.E. tubes".
I have used the 420A in place of 12AX7's in a preamp (re-wired), and the sound was harmonically rich and initially pleasing, but not accurate. Likely, for the reasons you have stated. They sounded like a really fat Mullard or old RCA black plate 12AX7. It was a fun 'roll' anyway.
Not exactly what I'd call an "HD" 12AX7 sub, if anything, the exact opposite.
Cory
Seriously, I have a whole box of Raytheon 5755. I thought many times about using it in a circuit but never got around to it. I bought them a long time ago. And seriously if you want a 5 pack of Raytheon 5755 shoot me an email and we can work out a good price. cheers, Dak
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: