From formercakid@yahoo.com Thu Jun 20 05:48:29 2002
Subject:Re: Swapping Out the H&K Rotosphere Tube

I had a theory but not being an electronics expert
like you guys I had no technical knowledge to back it
up. The theory was to try to simulate the preamp stage
of a real Leslie. After doing some research about
Leslies on the internet I found that the wood cab
Leslies had 12AU7 tubes in them. So I figured what the
hey! Put a 12AU7 in the Rotosphere and see what it
sounds like. I ran a Porta-B back in the 70's thru a
145 Leslie but heck if I remember what kind of tubes
it had in it. But I am slow not stupid so I checked
with H&K to make sure doing this mod would not damage
the Rotosphere circuitry and they reponded that it was
ok to do the mod and also some guys do it. You guys
have been much help........thx.
--- sgtpepper@rcsis.com wrote:
> OTOH it could be the 12AU7 you put in there was a
> noisy one. I think trying
> other tubes is a good idea. Why did you want to
> lower the gain?
>
> ---smc
>
> >Thx for the advice. The idea was to lower the gain.
> I
> >checked with H&K first and they reported some
> players
> >do swap out the 12AX7 for a 12AU7, guess it
> backfired
> >in my case. Cause the hiss is definately louder, I
> >will stick to 12AX7's, I have a couple of spares I
> can
> >try. But I agree with you regarding the design and
> I
> >am sure H&K must have tried numerous tubes before
> they
> >decided on the Ruby 12AX7. But then again it's
> gotta
> >be the tube that is producing the white noise. I
> had a
> >recommendaton do try old NOS 12AX7 tubes.
> >--- sgtpepper@rcsis.com wrote:
> >> 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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> >>

> >>
> >>

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> >>
> >>
> >>
> >
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