Is this a dumb idea?

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wayneosdias
Senior tube assistant
Posts: 226
(2/3/04 4:00 pm)
 Is this a dumb idea?
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 Ok, I just got the TOT by OConnor and was reading that that steel chassis's help sheild the magnet feilds away from the circuit inside. I have a high gain amp where the ot sits over the preamp section and the chassis is AL and their seems to be a mysterious noise i cant seem to get arid of. Would it help if i sheilded the ot? I was thinking that i could drill 2 hole in the bottom of a coffee can, feed the 1ary and 2aries thru, sit the ot in the bottom of the can then mount the can to the chassis. Would this in effect carry magnetic feilds away from the internal circuit? Anybody know of another way of accomplishing the same thing?

wayne
 
boogielicious
Junior tube assistant
Posts: 52
(2/3/04 5:09 pm)
 Re: Is this a dumb idea?
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 Try moving the OT around first and see if the noise changes. If you have enough lead that is.

Scott
 
wayneosdias
Senior tube assistant
Posts: 227
(2/3/04 7:37 pm)
 asdf
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 its a hand made chassis that will only work w/the ot in that spot. its a hammond 1608, at first it was real noisey but i sheilded the 1ary and 2aries w/quater in sheilding whcih seemed to help.

wayne
 
Lucid Alice
Senior tube assistant
Posts: 154
(2/4/04 1:03 am)
 Re: asdf
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 Yeah, I really can't understand the "only aluminum chassis are any good" thing. An aluminum chassis is inferior to a metal chassis with one exception... that is when one or more of the transformers are mounted through the chassis. If both transformers are bolted on the outside of the chassis a metal chassis provides better shielding for the circuits. While I wouldn't hesitate to use aluminum, I feel the same way about metal. I just don't get the "it-has-to-be-aluminum" thing in circumstances where it is the worst possible choice. A high gain circuit with externally mounted transformers would be a prime example of this.

 
wayneosdias
Senior tube assistant
Posts: 228
(2/4/04 1:33 am)
 asdf
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 Another example of this, I had an electar tube 10 amp that i did a few mods to including putting it into a AL chassis so i could also us a 12" speaker instead of the 8", after i fired it up in the new chassis adjusting the gain anything over 3-4 and it would hum like a banshee. I thought i did a mod wrong so went thru it completley and couldnt find anything, so i put iit back in its old chassis to reuse the AL chassis and cab. When i turned it on w/the old chassis i could turn the gain up to about 8 before it started making the same noise! Also another weird thing is that in the original setup the mico ot was mounted INSIDE the chassis next to the circuit, I replaced it w/a a hammond 125d on the outside, either way it was quieter w/the steel chassis -trippy-.

wayne
 
stan buczko
Junior tube assistant
Posts: 65
(2/4/04 9:12 pm)
 Re: asdf
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 My last scratch amp build i used an AL chassis. I made the chassis to a Marshall style but with these dim. 18"x8"x3". The trannys were outside mounted both facing the same direction at each end of the chassis about 8 1/2" apart with the choke in the middle. Power section is a 5f6a, preamp is a pexi/bassman combo with the hot mod, out put section is bassman wired with a Stromburg-Carlson op tranny. This amp can scream when you want it to and it runs pretty dang quiet too.
 
 
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