Re: [Harp-L] Fender Vibrosonic

[David Harris <snakehead_1@xxxxxxxxx>]

Hi Spec20,
  Putting a lower gain tube in the Inverter helps to reduce feedback. Wen lower gain tubes (Like a 12AXT) are used in the Normal channel, the feedback will be reduced even more.  Notice I say reduced not eliminated.
   
  A lower gain Inverter allows for more usable range in the gain controls.  In effect, the amp should be able to get louder if 12AU or 12AY tubes are put here.
   
  Putting lower gain tubes in the Inverter also introduces a nice "sag" that is great for harp.  Whereas the amp will usually be very clean, the lower Inverter tube will help introduce some breakup an distortion.
   
  Dave Harris

Special20 <special20harp@xxxxxxxxx> wrote:
  Why would you change the Phase Inverter tube?

-Spec20

On Fri, Mar 7, 2008 at 7:43 AM, David Harris wrote:

> Jim,
> My research show that this is the standard layout of the tube layout for
> the Vibrosonic:
>
>
> http://bb.steelguitarforum.com/viewtopic.php?p=1095549&sid=9b8d27feec6f14b61cf9263c596f73f2
> (Stock tube layout facing the rear of the amp)
> 4 6L6GC Power Tubes
> 12AX7A 1st stage gain
> 12AX7A 2nd stage gain
> 12AT7 Reverb Driver
> 12AX7A Reverb Return
> 12AX7 Tremolo
> 12AT7 Phase Inverter
>
> Is that close to your current setup?
> What I would suggest is concertrate on changing the Gain tubes and the
> Phase Inverter. Don't even use the Reverb and Tremolo for harp. You
> should, however, make sure that you replace any blown or worn out bulbs.
> Especially since you mentioned intermittent performance for the tremolo.
>
> Here are my suggested tube types:
>
> 12AX7 1st stage gain
> 12AU7 2nd stage gain
> 12AU7 Phase Inverter
>
> or
>
> 12AT7 1st stage gain
> 12AU7 2nd stage gain
> 12AU7 Phase Inverter
>
> or
>
> 12AT7 1st stage gain
> 12AU7 2nd stage gain
> 12AY7 Phase Inverter
>
> Try those and see how they sounds.
>
> Dave Harris
> http://www.myspace.com/superdharris
>
>
> "Priest, Jim" wrote:
> Anybody have any experience of, or views on, a Fender Vibrosonic Reverb
> as a harp amp? I just acquired one of about mid-70s vintage. It's in
> just-about-working order but has been in the wars somewhat and needs some
> TLC. It has a single 15-inch speaker (which looks like a replacement but has
> no discernable id), tubes are 4 x 6L6 power, MESA brand (one of which has
> blown) and 6 assorted pre-amp. It has in-built reverb (working) and tremolo
> (intermittent). And it weighs a ton!
>
> Any suggestions on tube config or upgrades/mods that will suit it better
> for harp?
>
> Cheers
> Jim
>
>
>
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