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Humm , Mid bass , and Russian 6sn7s and filaments

Posted by Satelliteman (A) on August 11, 2006 at 00:38:03

Hi there Tube techs ..well , I have to say that after replacing my radiotron & RCA mixture of 6sn7's for my first amp , ive now been hit with a dose of hummmmmm . This happened because I replaced all the 6sn7s with Eh 6sn7s ..as i didnt have a matching set of four for the 2nd monoblock . What was immediately apparent , was the new mid bass that I was missing before . However , with that , ive now become aware at a quiet listening level , a Humm that was just NOT what it used to be . Ive tracked this to V2 ...which is most significant in a swapout . If I change V2 with a Radiotron Australia for example , the Humm is gone , and I mean nill - zip - ear upto the speaker , and zippo - none . So thats with 3 Eh 6sn7 & 1 oddball 6sn7 in V2 , the hum is not hearable at 1ft from speaker. I guess that this is all about Heater ripple transfer internaly happening in the tubes . This is quite a first hand experience with NEW russian tubes , and the effects that they can have . At this stage , im siding to having an odd ball V2 in place , as my listening levels are normally on the quieter side of the m60 abilities. Speaking of heater / filament connections - What are the normal connections of the Output & Driver windings . I have it as follows ....Driver Transformer is wound with a 6.3 @ 3A fro the 4 6sn7's . The Transformer for the output stage's is All filaments on one bank ( x4 ) is supplies from a totally isolated winding from the other bank . So in a sense , the 6AS7g's are on their own bipolar supplies , and heater supplies also . I read on the forums that its possible to wire the driver stage in parallel with the Output stage , anotherwords , feeding them from the 30amp 6.3v toroid , instead of the driver txfrm . If this is so , this makes me feel that the output stage filament transformer secondaries must be common . Do I have this correct ?? I have tried to study many pictures , and cannot make out , if at all the filaments sections should be isolated from each other .
Currently I have wired them to be totally isolated from each other . Thats how I asked for the toroids to be wound . I asked for a 2 x 6.3vac @ 15 amp . - this allowed me to have truely isolated output stages within the chassis itself . HELP - have I gone over the top ?/\Stu

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Kimber Kable

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