[Harp-L] Re: Harp-L Digest, Vol 33, Issue 29

[Dina Janzen <dlj@xxxxxx>]

I am self-taught, so take my observations accordingly.....

Fender typically uses 2 W series resistors in the power supply.   Other 
manufacturers often use 1/2 W resistors, particularly at the preamp 
tube level. You should be able to get some idea of this on your amp by 
inspection of the resistor.   I use a standard size Alpha 200K pot 
mounted in a Lee Oskar harmonica box when I fuss with the series 
resistance.  I don't know the rating of the pot.  It has not failed.

Nothing personal, but......THIS WORK IS CONDUCTED WITHIN A FEW 
CENTIMETERS OF A SPOT WITH 450V DC DURING OPERATION.  THIS VOLTAGE MAY 
BE PRESENT EVEN WITH THE AMP UNPLUGGED BECAUSE THE POWER SUPPLY 
CAPACITORS ARE CHARGED DURING AMP OPERATION.  THE CHANGE MIGHT BE 
MAINTAINED FOR SOME TIME AFTER THE AMP IS TURNED OFF.  IF YOU DO NOT 
KNOW HOW TO DISCHARGE THE HIGH VOLTAGE AND DETERMINE IF THE VOLTAGE HAS 
BEEN SUFFICIENTLY DISCHARGED, YOU SHOULD NOT BE UNDERTAKING THIS.



On May 16, 2006, at 9:01 PM, harp-l-request@xxxxxxxxxx wrote:

> From: G <gigs@xxxxxxxxxxxxxxx>
> Subject: Re: [Harp-L] Low plate voltage on the preamp tubes?
> To: harp-l@xxxxxxxxxx
> Message-ID: <3.0.3.32.20060517125348.01b2df04@xxxxxxxxxxxxxxxxxxx>
> Content-Type: text/plain; charset=us-ascii
>
> Date: Mon, 15 May 2006 22:23:28 -0500
> From: Dina Janzen <dlj@xxxxxx>
> Subject: Re: [Harp-L] Low plate voltage on the preamp tubes?
> To: harp-l@xxxxxxxxxx
>
> > I agree that reducing the plate voltage of Fender....

> > Jim R
>
> Hi Jim,
>   Basic question: What kind of wattage do the resistors or POT have to 
> be
> for this sort of thing?
> -- G.