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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Heaters The Key Too Sweet Tube Tone.

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All Tube sound better with Lower Heater.6.3,12.6 not real,Ac at your home moves around,117,115 in day,122 or higher in night,
One way to see if i am right is to CK your heater V, I say you will find there High.At All times.
Well how well i lower my AC heaters, well it EZE, i Use more tube sockes, Just let them hang off to the side for now,Just too see if i am Right,the Tube it self is the best Sound,ing way to lower the V,AC or DC just add more till the V drop,All the Amps To day an of Old i have found have more heater V An Amps, On Amps THe oUT put Tube, i like 6AS7,s drop 6.3 from what i see most 6.5-6, Drop to 6.2 your sound well be sweet,er Righ Off, same 12.5-7, add more tubes ,just heaters Are all were doing here Just Run the Heaters to the new Sockes! Get them To12.2 ,6.2or lower but just lower than 6.3 or 12.6 you well not think it the same amp or preamp,All can have Sweet Tube tone,
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In my experience, several of the modern small signal triodes do indeed sound better with slightly lower filament voltages (6DJ8, 6HM5 and 6J4 are a few that I have noticed this with); however, I have not found this to be the case with any octals (6SN7, 6SL7, 6EM7, or 6BL7 to name a few).
I agree with Ray that power tubes should run at their specified filament voltage.

Jim
 
lower heater,s Sweet Tone

It started for me when i Got a HH Schott 60 year old preamptuner Type 355,it had all the tubes but did not come on so i got it for nothing in a deal,got to looking at it an found the Heater had shorted out,a wire fell off,found the wire got it going,got love tubes ,well found the Heaters were at 5.8,Well that cant be right.Got a Schematic, an yes 5.8 was what thay set it up at,an the 12AU7 out of the 355 is as sweet as any 5k or more preamp i have had.So you say that output tubes can be ran high well that means if you get 6.1-2 at the low of the day at the high of the day you well be just right, but any one how wont to get sweet tone out of the tube well say the low is sweeter.i have now 4 Dynaco MK3s 1 JoLida 502a an a Amthem Amp One, All are at 6.5-7 at the low an 6.9 at high at night,The dynaco are the EZEst thay have the Preamp plug on the Frount An were set up with more heater V.To run more tube in the preamp,just put a 6AS7 or any big 8 pin tube in there,the 70s are the same thay have two ready the 6AS7 pull a lot of amps 2.3 pre tube i think,any way you well hear a diff. right off
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In my experience, several of the modern small signal triodes do indeed sound better with slightly lower filament voltages (6DJ8, 6HM5 and 6J4 are a few that I have noticed this with); however, I have not found this to be the case with any octals (6SN7, 6SL7, 6EM7, or 6BL7 to name a few).
I agree with Ray that power tubes should run at their specified filament voltage.

Jim

My experiences jibe closely with Jim's comment, and further it was usual practice in RIAA amplifiers to run 12AX7A slightly cool in order to reduce thermal noise. (Look at old Dyna PAS 3, etc..) Filament voltages of 5.5V/11 volts were not uncommon, however plate currents were also deliberately relatively low - in the <500uA range in some cases.

In terms of some dhts some people (Steve Bench amongst others) determined that in some cases running them below rated filament voltage resulted in better linearity. Doing this requires some care to assure that the space charge around the filament is not depleted in operation - usually by reducing nominal plate current by some %. I have done this with some low voltage sub miniature dhts and noted some improvement in thd.
 
Heaters

Well one thing we know is NO high heaters Sound as good as lower Ones,I have set up there owen Heater Xfourmer.An have lower the 6.5-7 an 12.5-8 down with res.like 1/2ohm 40watt,dose not sound as good,an yes i am all about the Sound
I think it may be that the Xfourmer may need to pull more Amps, like a class A mosfet amp ,the more Amps thay pull the better thay sound well till thay pop, Ha, An i have Found that the Power Xfourmers that,s runing the tube Heaters to high Run Hot,er Than when All the tube are lowerd by adding more tube heaters. May be the Higher heaters Run out of Head Room. Say the Xfourmer Heaters winding is 6 amps an the tubes are only pulling 4 Amps into High heaters,
But i say All Amp heaters Are TOO high...To sound as sweet as thay can,No matter What tube or setup pushpull SE.class A,AB, An yes the tube used to pull down well give a diff. Sound the 6AS7 to me sound like A good ONS 6L6
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thanks
 
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