Re: Fender 40W Blues Deluxe Amp Opinion

[Markburness@xxxxxxx]

I've never heard of Gerald Weber recommending cold bias for harp, nor larger 
than stock input loads. As far as I know, as at least a year ago, all 
Kendrick harp amps, and all Kendrick amps for that matter, used 1 meg 
resistors for the high gain input.
He does recommend plate voltages on the preamp that are typically lower than 
found on modern guitar amps and is the source for this particular suggestion.

Yes, these mods could be done to many amps, especially fixed bias A/B 
Fenders. The size of the input resistor would depend on the choice of mic and 
whether or not you used any pedals/effects between mic and amp. 5Meg plus may 
damage fidelity for Hi-Z dynamics straight in, but up to 10 meg is fine for 
Astatic mics, maybe larger if they have a volume pot in - order to stop the 
input resistor & pot from pulling down the impedence of the input circuit. 
The larger values will also help keep the signal strong when using effects, 
though ideally the effect in question should also have a high input impedence.

Cold bias is relatively simple to achieve and reduces gain/feedback in the 
output section. The resultant tone can be drier/crunchier and not to 
everyone's taste, the exact current will depend on the listener's idea of 
tone. A 40W, 4x10 amp may not "sound" particularly cold running 10-15mA but 
will feedback much less than the same amp at 30mA. I haven't tried cold bias 
for cathode biased amps and I'm quite happy running my cathode biased amps 
between 40 & 70mA depending on the model. Other list members have suggested a 
slight mismatch in power tube bias currents can be advantageous (again, this 
has its roots in Mr Weber's article but anyone who has messed about with a SF 
Fender may have come to the same decision).

Larger than stock cathode bypass caps in the preamp are an accepted method 
for voicing preamp stages. IE Fender's Bassman used a 250uf (220uf on the RI) 
bypass cap in the first stage, compared to 25uf on a "voiced for guitar" 
Concert or Super Reverb. No cap at all will give less gain but a clearer, 
wetter sound. 

Exact perameters for any of these mods depend heavily on the players ear and 
tone desired.

Regards, Mark.