Re: [Harp-L] Feedback

[Rick Davis <bluesharpamps@xxxxxxxxx>]

Mark, exactly right.

Greg, can you please define "Power Tube Saturation" as it applies to harp
amps such as the Bassman types?

Thanks.

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





On Sun, May 1, 2011 at 11:56 AM, MARK BURNESS
<markwjburness@xxxxxxxxxxxxxx>wrote:

> Greg wrote: "But when all is said and done, the single most valuable change
> you
> can make to make an amp more harp friendly is to reduce the gain of the amp
> through tube substitution." In many cases tube subs are very useful, but
> some
> amps are much less tolerant to lower mu tubes (most guys I know that run
> brown
> tolex Fenders like Concerts & Bandmasters use 12AX7, John Kinders amps used
> 12AX7). In many high powered amps, running the phase inverter at high
> voltages
> (the preamp tube that is next to & drives the power tubes), subbing a 12AX7
> for
> a 12AU7 can burn out the plate resistors, I wouldn't do it in a Blues
> Deluxe/Deville, as these occasionally fail even with a 12AX7 installed (if
> this
> resistor does fail it can usually be replaced for the tech's minimum
> charge/bench fee, so if you feel it gives a substantial benefit you may
> well
> decide the risk worth taking). In all cases it's probably best to not try
> and
> put all your eggs in one basket regarding feedback, output tubes have gain
> too
> and this can be reduced by rebiasing cooler, in a sympathetic amp/design
> (as
> long as this doesn't push up operating voltages beyond what tubes & caps
> will
> stand). Feedback can be affected by all stages in the chain - mic, preamp
> tubes,
> any guitar oriented bright caps & tone filters that increase high end,
> power
> tubes & bias, rectifier & speaker choice. Sometimes one or two aspects can
> provide a useful advantage, other times you have to utilise other avenues,
> either seperately, or in combination..
>
>
>
>
>
>