Other web Sites
Harmonica Blues  Harmonica Amps
Harmonica Links Harmonica Pages
• Archives Home
• Years
 · 1992
 · 1993
 · 1994
 · 1995
 · 1996
 · 1997 		 · 1998
 · 1999
 · 2000
 · 2001
 · 2002
 · 2003
 
Web HarpL
Ebay Searches:
Amps:
Microphones:
Effects:
Harmonicas and Gear:
Harmonica Music and Instruction:

 

 

Harp-L Archives

[Previous Message] [Next Message]
[Previous in Thread] [Next in Thread]
[Start of Thread] [End of Thread]

Date: Fri, 31 May 2002 17:57:39 EDT
From: Markburne~ol.com
Subject: Re: Preamp tube subs revisited (was: Bassman '59 RI)

Hi John,

If it were the case that lower preamp valves just gave you more sweep on the
knob then surely substituting the, usually 1 meg, volume pot for say 500K
would have the same effect.? This is something that I have considered, but
never felt the need to do, where tube subs are not an option (BF/SF
Fenders).
Changing the pot would give you more play but would not substantially change
the tone produced (though it may possibly be more consistent due to the
decreased sensitivity of the pot).

Lesser gain preamp tubes change the tone considerably as they react
differently to AX's when put in the same circuit - the lesser gain structure
and reduced voltage both serve to reduce acoustic feedback. To summarise an
AX has a gain structure of 100, AT/5751=70, AY = 40, AU = 20 (ish).
They certainly can allow more volume (db) but the shape/cut of the sound may
be affected in such a way as to lessen the audible impact. All things being
equal, the more gain you have the better your amp will push the low
frequencies...it's a question of balancing this against the feedback issues
and volume requirements. Too much gain and the tone can be "flat" and
lifeless.

Experimentation is the key, preamp tubes are cheap, assuming you manage to
put them in the right way (observe the pin layout/keyway) the worst you
might
do is burn your fingers/upset the neighbours. (I'm sure I don't need to
point
out that your amp should be turned off, allowed to cool and unplugged from
the wall before changing tubes.)

Regards, Mark.