Re: [TCML] VTTC grid/secondary coils

[Simon <elmontare@xxxxxxxxx>]

Hello all, 

So i tried switching out all the capacitors with different ones and still no go.  I then figured i would just change things back to how they were when it was for sure working. Strangly though it didnt work. 

I noticed though that only two things are different:  i now have the wood its mounted on sealed with polyurethane AND the leads going from the coil to each individual grid of the tubes (theres 4 vacuum tubes in parallel) are slightly different lengths. The difference between 2 of the tubes is only about 2ohms measured from the top end of the grid coil to each pin of the tube but in all my other setups the wires were pretty much exactly the same length. 

Could either one of these be a factor?

This may or may not be related but one time i had the diode backwards on the voltage doubler circuit and i got the horrible feedback on the variac at about 10vin. Reversed it and it worked fine  So i tried to duplicate that with a spare diode i had just to get some sort of sign from this vttc but i couldnt reproduce that feedback noise. Related?

Any other advise or comments would be appreciated, thank you. 

Simon


On Aug 27, 2012, at 12:25 AM, Steve Ward <steve.ward@xxxxxxxxx> wrote:

> Simon,
> 
> The issue should have been resolved by swapping the leads of only the
> grid coil.  As long as your primary orientation stayed the same, you
> should be able to effectively reverse the grid coil winding by
> swapping the leads.  For such a short coil as this, top and bottom
> shouldnt matter.
> 
> Maybe your capacitors are bad?
> 
> Steve
> 
> On Sun, Aug 26, 2012 at 11:14 PM, Simon <elmontare@xxxxxxxxx> wrote:
>> So long story short - i made some recent changes to my vttc coil concerning the primary circuit and grid coil. The changes i made were:
>> 
>> Changed the tank capacitance from 5nf to 2.5nf and thus increased the number of primary turns (and the diameter by about 1/8"). I also rewound the grid to match the new primary diameter.
>> 
>> Ive made plenty of changes like this and have been able to get things working one way or another so i dont think its the "stats" of the coil causing a problem. The only variable i can see is the physical winding direction of the grid is NOW the same as the secondary. In all other setups it has been wound opposite. Is this a problem??
>> 
>> I havnt tried rewinding the grid yet, but i have tried everything else and still no sparks, not even a "feedback" hum from the variac.
>> 
>> Things ive already tried:
>> I had an analog ammeter in series on the grid coil after the capacitor before ground and wasnt reading anything anymore. Ive switched all the leads going to the primary and grid. Checked along the secondary with a neon light. Physically flipped both grid and primary coils. Tried various tap points and slight changes in coupling values for the coils. Ive checked the frequencies with an O-scope and assuming i did that right everything is as close as it ever was.  Ive taken voltage measurments all over the circuit and things seem right.
>> 
>> Thanks for thoughts.
>> 
>> Simon
>> 
>> 
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