RE: Variacs : Was Re: Amp Rectifiers

["Paul Harker" <paul-harker@xxxxxxxxxxx>]

Why I believe Variacs are a bad idea:

>From http://www.drifteramps.com/safety.html

VARIAC - Sure, Eddie Van Halen made use of a variac to get his tone.  A
variac is a VARiable AC supply.  Running an amp at a higher voltage than it
is designed is a sure way to ruin the amp.  Likewise running at a lower
voltage can cause serious problems due to the heaters in the tubes running
too cold, which can lead to cathode stripping, which leads to shorter tube
life, which can sometimes cause other problems.  The best way to use a
variac is NOT to use one.  A variac is to only be used for repair and
building purposes as a piece of bench test equipment.  EVEN if you use a
variac to regulate your line voltage, which is a good thing seeing how line
voltage can vary from place to place AND most vintage amps were designed to
run at a slightly lower voltage (110VAC) versus what most line voltage is
now (120VAC), having one on stage is just asking for your drummer, or anyone
else nosing on the stage to play it and see what kind of fun they can have.

- -----Original Message-----
From: owner-harp-l@xxxxxxxxxx [mailto:owner-harp-l@xxxxxxxxxx] On Behalf Of
Russ Bradley
Sent: Tuesday, April 06, 2004 5:45 AM
To: party_man1@xxxxxxxxxx
Cc: harp-l@xxxxxxxxxx
Subject: Re: Variacs : Was Re: Amp Rectifiers


So, what I hear you saying is:
A variac won't hurt your circuit as long as you are not letting the 
voltage exceed 120V AC.
The way to use a variac with an amp is to lower the voltage for earlier 
breakup.

Can anybody else out there confirm this?  I have read tons of warnings 
about using variacs with amps, so this is news to me.  But this does 
make sense.  Voltage lower than 120V AC shouldn't burn anything up.  And 
Gerald Weber does recommend low plate voltage on the preamp tubes..

Thanks,
Russ

party_man1@xxxxxxxxxx wrote:

>Richard Smith sez :
>
>
>  
>
>>In some amps designs, a tube rectifier is prone to voltage "sag" when >the
amp is pushed to the max. This sag (lowering of plate voltage) >causes tubes
to distort/crunch earlier, changing the tone. Eddie Van >Halen is famous for
loving the sound of early distorting tubes, and >would run his amps on a
variac to artificially lower plate voltage. >(Don't do it! Eddie can afford
to have his amps rebuilt on a regular >basis)
>>    
>>
>
>  
>
>>A solid-state rectifier won't sag. Its not a matter of good/bad -- >more
>a matter of taste. FWIW, most amps now have solid state >rectification.
>>    
>>
>
>=========================================================================
>
>Hurricane sez ;
>
>Richard :
>
>The topic of variacs has been a thread that spurs allot of controversy
sometimes from those who do not know how to use them . Judging from your
e-mail , it appears to me  ( ¿ at least I think ? ) that you know about them
and their proper and safe use . But for those that do not , I thought I
would add to this thread of amp rectifier's topic that you mentioned about
variacs .
>
>Yep a varic will help you to get that " crunch " . I put one on my Marshall
50 Watt tube with twin Celestions ( oooo what a sound ! ) and it made it
play that crunch distortion at any volume instead of only at high sound
pressure levels , and I might comment it never hurt it or cause tubes to
wear out quickly or hurt the transformer , I had  this amp 5 years and only
replace the tubes once and used it all the time , it was a work horse for me
, the fellow who bought it was a Stevie Ray Vaughn type guitar man and fell
in love with it at once when he heard me " tweak " it to a small room
performance one night . I bought the Marshall at a yard sale , it was beat
up with all sorts of little nasty things I had to fix , but most were
cosmetic , it was about 7 to 9 years old when I got it .
>
>
>This is a super advantage to maintaining your " signature sound " in any
size room . This is important if you have a rig ( tube amp )that's high
powered like a Fender Bassman or any tube amp with 50 watts or more . What
sounded great in a large hall with lots of people and noise will blow the
patrons out of the small coffee shop when you let that puppy get to the
sound you desire . The vairac serves to compensate for the size differential
of one room from another . 
>
>This regulation of input voltage to your amp  is a cool thing as it lowers
the voltage and giving you a " safe " way of getting that sound of "
crunchville at lower power levels . There have been comments made of this
being an " unsafe " thing to do and it can be if you don't realize how to
use one properly . The biggest mistake I have seen that has caused problems
is when some one turns up the "  rheostat " that controls the input voltage
to your  amp and fries something like the tubes and or a x-former ouch !
>
>These kind of failures can be remedied and avoided easily by using a volt
meter to see where 120VAC is on the rheostat dial exactically , its
important to get a true understanding of the line voltage maximum's because
some believe that to get the full 120 VAC , you need the rheostat turned to
the max position , this  seems the logical thing to do but it ain't .
>
>
>
>At the optimum setting ( rheostat turned up till it can not be advanced any
more ) you might be pushing into your amp 130VAC , 140 VAC or much more as
it varies from one city to another or one neighborhood to an other or one
variac to an other  as far as individual characteristics that determine what
their out put voltage is from the variac. Once you know for sure where the
max is on the variac , you are in the " safe zone " @ 120VAC or lower ,
because no matter how low you reduce the voltage it will not hurt the amp or
its innards :-) . If you don't have a multi-meter , just go to a electronic
service and repair techs shop and ask them to show and mark where
exactically the max 120VAC is , and from there enjoy the ride like Eddie Van
Halen and many others who use(d) them , like Hendrix or Stevie Ray Vaughn ,
etcetera.... .
>
>
>I'm sure that this post will get plenty of " no no no's " it will fry you
amp stuff and its O.K.  , but to be honest this type of electric hot rodding
is not for the novice , it is however for  the semi-pro , and professional
who has already gotten way past the beginners stage and has a great command
of what he is doing on stage as well as great command in his tone and chops
.
>
>For the novice harper :
>
>By purchasing a " Fender Champ " type tube amp ( there are suitable others
out there in the tube family , it doesn't have to be a Fender ), you will
get that effect of the crunch that will more than likely be perfect in a
small room , so for you guys , its no biggie not to have a variac .
>
>For the semi & pro's :
>
>If you have a tube amp with some muscle , the variac is not a bad choice
instead of getting an additional ( $ )  lower wattage amp for small rooms .
After I sold my Marshall because it was a back breaker ( and more so with
the added weight of the variac ) ,  I got ( besides another lighter 60 watt
tube Carvin with only one 12" speaker ) , several smaller tube amps because
the added weight of a varic to a already heavy cabinet and amp is not what I
want any more . I use a Skylark Gibson ( circa 1950's ) & an old timy baby
Gretsch ( circa early 1940's ) .  But I still like what a vaiac does , even
to these small amps :) , it is a really fine way to "tune in " that sound
everyone seeks in a Chicago break up crunch sound for the harp  .
>
>Its a matter of choice I suppose . Like the old saying " There's more than
one way to skin a cat " applies here & " Look before you leap into a variac
" is also a cool  thing to know . But to protect my @$$ , YMMV :) 
>
>Sincerely :
>
>HR
>
>aka:
>
>Party_Man1@xxxxxxxxxx  
>   
>
>
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