From steve@speakeasyvintagemusic.com Wed Jun 19 16:00:03 2002
Subject:Re: Swapping Out the H&K Rotosphere Tube

Hi

Smc is right. Not only is the gain way off. The plate resistance is
completely wrong. The 12ax7 has a gain of 100. The 12au7 is 17. The
difference in the resistance is major. 12ax7 is 85K / 12au7 is 6500. This
will upset the balance in the circuit.

Shayes

Steven Hayes Sr Engineer
Speakeasy Vintage Music
http://www.speakeasyvintagemusic.com
----- Original Message -----
From:
To:
Sent: Wednesday, June 19, 2002 4:37 PM
Subject: Re: [CWSG] Swapping Out the H&K Rotosphere Tube

IIRC from my guitar-amp-building days (in the late 60's), the 12AU7 is a
much
lower-gain tube than the 12AX7. If the Rotosphere is designed for the
12AX7,
shouldn't you stick with that type? I think (this is a guess) you are now
putting
out a lower-amplitude signal, but the white noise level is the same as
before--resulting
in a poorer signal to noise ratio.

--smc




I recenly swapped out the Rotosphere tube. Going form the stock Ruby

12AX7 to a JAN-Philips 5814 12AU7. Although the tone became a little

warmer after the swap I noticed that the hiss(white noise)that the

Rotosphere produces got a little louder.



Has anyone out there experimented with swapping the Rotosphere tube

out with other brands/makes/types of tubes? If anyone has I would

appreciate their feedback as to how the tube swap affected the units

noise(hiss) level.



We could all save each other alot of money if we share are results,

ause tubes are really expensive these days.








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