Re: [Harp-L] amplification question - unbalanced PI

[Special20 <special20harp@xxxxxxxxx>]

I tested the feedback-fighting properties of the 12DW7 PI tube at the
Blues Harp Amps Blog.  You can read the article at this link:

Testing the 12DW7 Phase Inverter Tube
http://bluesharpamps.blogspot.com/2008/06/testing-12dw7-phase-inverter-tube.html

-Rick Davis
The Blues Harp Amps Blog
http://bluesharpamps.blogspot.com/



On Thu, Jun 26, 2008 at 5:52 AM, john <jjthaden@xxxxxxxxx> wrote:
>     I'm playing out a lot now in many different styles, in both large
> and small rooms, often with loud guitars in the band. I now use an
> Electrovoice EV 630 Dynamic omnidirectional bullet, wired Hi-Z into
> a Premier 50 amp that I usually mic through the PA, trusting the
> soundman, when there is one. It usually works great, but I can be
> easily overpowered, and its certainly not the bassy, wall-of-sound
> result I can get from playing a 4-10 rig like a Bassman RI.
>     I've been thinking a lot about amplification alternatives,
> for instance, I posted recently asking what folks thought about
> Rocktron Minihush and Hush pedals to control feedback, a
> problem I had last week when, knowing I would be onstage with
> two powerhouse guitarists and no PA mic'ing, I tried to drive my
> the speakers of my ailing Blues DeVille with an old Newcomb 25
> PA head.
>     Today's question is whether anyone has an opinion on a claim
> I read this morning that harp amplification through a push-pull circuit
> like a Bassman RI benefits fron an unbalanced phase inverter tube.
> I found this at http://eurotubes.com/euro-l.htm:
>
>     Third on the list is Harp players. For power I use the same lineup
>     as I do for Blues players and then I drop the V1 and V2 tubes to
>     ECC81's and the use an ECC832 in V3. To make a good harp
>     amp the phase inverter tube needs to be unbalanced which is the
>     opposite from the way a good guitar amp should be which is with
>     a nicely balanced PI tube. For some odd reason harps just sound
>     good with an unbalanced PI tube, this is the preamp tubes that's
>     right next to the power tubes ( V3 ). By going with an ECC832
>     ( 12DW7 ) tube which is one half of a 12AX7 and one half of a
>     12AU7 this puts the power tubes way out of phase and it sounds
>     good and cuts down the feedback for harp. On the other hand it
>     does not sound good for guitar
>
> Thanks for reading,
> -John T
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