Funkalicousgroove wrote:Thing is, they are 90 degrees of eahother, and an express Hums a plenty- we just deal with it here in guitarville
The Express trannies are essentially round the wrong way though. The endbell of the PT should face the stack of the OT to minimise magnetic coupling there. It should still be far enough away from all of the tubes to have minimal impact on them as it's an inverse square law.
If you imagine a figure 8 of magnetic flux then the two loops start from the sides of the stack, so the endbell side is the quietest.
Not Ken's strongest design point in that build, but then there wasn't enough room on the chassis to have them round that way without putting them side by side like a Dumble or Marshall.
This is somewhat of a head scratcher here as he had plenty of room to put the OPT in the traditional spot behind the power tubes..The hole you see just to the left of the transformers is another wooden dowel that helps support the chassis..He could have put the OPT in the usual behind the power tubes and would have worked just fine..Anyone who knows Ken knows how anal he was about his amps which leads me to believe he had some other reason for doing this.. Also check this out same amp... He has V1/V2 filaments wired out of phase...I would imagine for hum canceling..I was always told wiring them out of phase will cause hum. A friend of mine has 2 Wrecks and both sound amazing and are very quiet... Express and Liverpool very early ones.. Norm sorry again for the hijack..
Tony VVT
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I have also read that you usually wire the filaments in phase but not necessary only when you run DC? So I still scratch my head, good thing I have plenty of hair. I am starting to think that I would like to build another 30 watt amp using unorthodox building methods and see what happens hum wise and all. Some amp builders have the OT and PT completely on opposite ends of the chassis that has to help in some way right?
I think Kens choice had more to do with the structural integrity of the chassis than anything, if you put that stancor in the middle of a .04 aluminum chassis it will bow , put it right next to a fold and it sits fine.
I think typically you want the OT as far from the input end as is practical.
As we know, anything that finds it's way into the first stages gets magnified many times.
As far as mounting the PT, OT and choke, check this out.
I didn't have any room for the classic layout and this was the way it ended up.
Very little hum or noise. Although I do have a oscillation if the tone and volume are pegged. But that is more of a lead dress or tube proximity problem due to having the circuit board on top of the tubes.
I would only be concerned about wiring them in phase when dealing with the power tubes, to get a humbucking effect by the hum being cancelled out via the two sides of the OT with equal amplification at all of the parallel tubes.
As regards preamp tubes, who knows which way the two filaments are actually oriented within the two triodes? Is their construction definitely such that the ac hum will be induced in the same phase in each triode? Even if it is, and the two triodes are operating in opposite phase as is normal, the noise from the preceding triode is still going to be significantly amplified anyway even if its phase is flipped so I can't see any real advantage to be gained.
For me personally I've had ony 1 issue with transformer proximity...(1/2 inch w/ Axis reversed)
If there is an issue there the amp will have a 60 cycle hum in stand by...
If you have to put them close together say within an inch or so I would shift the Axis for insurance anything over say 3 inches wouldn't really matter..I think it then becomes a preamp tube proximity issue and I always have the bell facing the tubes and never had an issue... Does how you orient them effect tone... Further than 3 inches apart I would say not really...
I was wondering about the hum bucking of the heaters of 12a*7 tubes myself.
I thought I had read somewhere that it has to do with the spiral winding of the heater element but I'm not positive about that.
It would seem that proper phasing of the heater wires would be a necessary thing to do.
That is, keep pins 4&5 on the same wire and pin 9 on the other.
